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Caution: Federal law (U.S.A.) restricts this device to sale by or on the order of a physician.
To contact Mallinckrodt’s representative: In the United States, call 1.800.635.5267 or 314.654.2000; outside the United States, callyour local Mallinckrodt representative.
0123
2001 Mallinckrodt Inc. All Rights reserved. 062153C-0701
SERVICE MANUAL
N-20PA Portable Pulse Oximeter
Nellcor Puritan Bennett Inc. is a wholly owned subsidiary of Mallinckrodt Inc. Nellcor and Nellcor Puritan Bennett aretrademarks of Mallinckrodt Inc.
To obtain information about a warranty, if any, for this product, contact Nellcor Technical Services or your local Nellcorrepresentative.
Covered by one or more of the following U.S. Patents and corresponding foreign patents: 4,621,643; 4,685,464; 4,700,708;and 4,770,179
Nellcor Puritan Bennett Inc.4280 Hacienda DrivePleasanton, CA 94588 USATelephone Toll Free 1.800.NELLCOR
Tyco Healthcare UK LTDFareham RoadGosportPO13 0ASU.K.Tel: +44.1329.224000
iii
CONTENTS
Contents................................................................................................................................................................... iii
Figures..................................................................................................................................................................... iv
Tables ....................................................................................................................................................................... v
SECTION 1: Introduction....................................................................................................................................1-1
1.1 Manual Overview..........................................................................................................................................1-1
1.2 Warnings, Cautions, and Notes.....................................................................................................................1-1
1.3 Description of the N-20PA Portable Pulse Oximeter ...................................................................................1-1
SECTION 2: Routine Maintenance.....................................................................................................................2-1
2.1 Overview .......................................................................................................................................................2-1
2.2 Cleaning........................................................................................................................................................2-1
2.3 Periodic Safety and Functional Checks ........................................................................................................2-1
2.4 Battery...........................................................................................................................................................2-1
SECTION 3: Performance Verification...............................................................................................................3-1
3.1 Introduction ..................................................................................................................................................3-1
3.2 Required Tools and Equipment.....................................................................................................................3-1
3.3 Performance Tests ........................................................................................................................................3-1
SECTION 4: Troubleshooting .............................................................................................................................4-1
4.1 Introduction ..................................................................................................................................................4-1
4.2 How to Use This Section ...............................................................................................................................4-1
4.3 Who Should Perform Repairs .......................................................................................................................4-1
4.4 Replacement Level Supported.......................................................................................................................4-1
4.5 Obtaining Replacement Parts .......................................................................................................................4-1
4.6 Troubleshooting Guide .................................................................................................................................4-1
SECTION 5: Disassembly Guide .........................................................................................................................5-1
5.1 Introduction ..................................................................................................................................................5-1
5.2 Beginning Disassembly.................................................................................................................................5-1
5.3 Disassemblying the Printer/Flex Circuit Assembly.......................................................................................5-4
SECTION 6: Spare Parts .....................................................................................................................................6-1
6.1 Introduction ..................................................................................................................................................6-1
6.2 Spare Parts List ............................................................................................................................................6-1
SECTION 7: Packing for Shipment ....................................................................................................................7-1
7.1 General Instructions .....................................................................................................................................7-1
CONTENTS
iv
7.2 Repacking in Original Carton ......................................................................................................................7-1
7.3 Repacking in a Different Carton...................................................................................................................7-1
SECTION 8: Specifications..................................................................................................................................8-1
8.1 Performance..................................................................................................................................................8-1
8.2 Alarms...........................................................................................................................................................8-1
8.3 Electrical.......................................................................................................................................................8-2
8.4 Environmental...............................................................................................................................................8-2
8.5 Physical.........................................................................................................................................................8-3
SECTION 9: Technical Supplement....................................................................................................................9-1
9.1 Introduction ..................................................................................................................................................9-1
9.2 Functional Overview.....................................................................................................................................9-1
9.3 Definition of Terms .......................................................................................................................................9-5
9.4 Overall Block Diagram.................................................................................................................................9-6
9.5 SpO2 Analog Circuitry .................................................................................................................................9-6
9.6 Digital Circuitry..........................................................................................................................................9-12
9.7 Circuit Illustrations.....................................................................................................................................9-31
FIGURES
Figure 5-1: Sensor Lock, Printer, Paper, and Battery Access Doors.........................................................................5-1
Figure 5-2: N-20PA Covers with the PCB and Display Assembly ............................................................................5-2
Figure 5-3: Main, Auxiliary, and Display PCB Assembly .........................................................................................5-3
Figure 5-4: Printer and Flex Circuit Assembly..........................................................................................................5-4
Figure 9-1: Overall Block Diagram...........................................................................................................................9-1
Figure 9-2: SpO2 Analog Block Diagram..................................................................................................................9-2
Figure 9-3: N-20PA Hardware Block Diagram..........................................................................................................9-3
Figure 9-4: Power Supply Block Diagram .................................................................................................................9-4
Figure 9-5: Display Control Block Diagram ..............................................................................................................9-4
Figure 9-6: Printer Control Block Diagram................................................................................................................9-5
Figure 9-7: SpO2 Analog Circuitry Block Diagram...................................................................................................9-7
Figure 9-9: Differential Synchronous Demodulation Circuit .....................................................................................9-9
Figure 9-11: Variable Gain Circuit ..........................................................................................................................9-10
Figure 9-12: Filtering Circuit ..................................................................................................................................9-11
Figure 9-14: Digital Circuitry Block Diagram .........................................................................................................9-13
Figure 9-16: Address Demultiplexing Circuit ..........................................................................................................9-15
Figure 9-17: Address Decoding Circuit ...................................................................................................................9-16
CONTENTS
v
Figure 9-18: CPU Memory Circuit .........................................................................................................................9-17
Figure 9-19: Input Port Circuit.................................................................................................................................9-18
Figure 9-21: Real-Time Clock Circuit .....................................................................................................................9-19
Figure 9-22: Audio Output Circuit ...........................................................................................................................9-20
Figure 9-24: User Controls Circuit...........................................................................................................................9-23
Figure 9-27: Analog Reference Voltage Circuit.......................................................................................................9-26
Figure 9-28: Ambient Light Circuit..........................................................................................................................9-27
Figure 9-29: Ambient Temperature Circuit..............................................................................................................9-27
Figure 9-30: Battery Voltage Circuit........................................................................................................................9-28
Figure 9-31: Battery Type Circuit ...........................................................................................................................9-28
Figure 9-8: LED Drive Circuit ................................................................................................................................9-33
Figure 9-10: N-20PA HSO Timing Diagram ..........................................................................................................9-35
Figure 9-13: AC Variable Gain Control Circuit......................................................................................................9-37
Figure 9-15: CPU Circuit ........................................................................................................................................9-39
Figure 9-20: Output Port Circuit .............................................................................................................................9-41
Figure 9-23: Display Control Circuit ......................................................................................................................9-43
Figure 9-25: Power Supply Circuit .........................................................................................................................9-45
Figure 9-26: Power Control Circuit.........................................................................................................................9-47
Figure 9-32: Printer Interface Circuit......................................................................................................................9-49
Figure 9-33: Printer Flex Circuit .............................................................................................................................9-51
Figure 9-34: N-20PA Main PCB Schematic Diagram ............................................................................................9-53
Figure 9-35: N-20PA Auxiliary PCB Schematic Diagram......................................................................................9-55
Figure 9-36: N-20PA Flex Circuit Schematic Diagram ..........................................................................................9-57
TABLES
Table 4-1 : Troubleshooting the N-20PA..................................................................................................................4-2
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1-1
SECTION 1: INTRODUCTION
1.1 Manual Overview
1.2 Warnings, Cautions, and Notes
1.3 Description of the N-20PA Portable Pulse Oximeter
1.1 MANUAL OVERVIEW
This manual contains information for servicing the N-20PA portable pulseoximeter. Only qualified service personnel should service this product. Beforeservicing the device, read the operator’s manual carefully for a thoroughunderstanding of its operation.
1.2 WARNINGS, CAUTIONS, AND NOTES
This manual uses three terms that are important for proper operation of thedevice: Warning, Caution, and Note.
1.2.1 Warning
A warning precedes an action that may result in injury or death to the patient oruser. Warnings are boxed and highlighted in boldface type.
1.2.2 Caution
A caution precedes an action that may result in damage to, or malfunction of, thedevice. Cautions are highlighted in boldface type.
1.2.3 Note
A note gives information that requires special attention.
1.3 DESCRIPTION OF THE N-20PA PORTABLE PULSE OXIMETER
The Nellcor
N-20PA portable pulse oximeter provides noninvasivemeasurement of, and continuous information about, the percent of oxygenatedhemoglobin compared with total hemoglobin and pulse rate. A pulse amplitudeindicator provides a qualitative indication of pulse activity and patient perfusion.Patients are connected to the instrument by a Nellcor sensor. The sensor LEDsare driven by the SpO2 analog section, which also conditions the incomingsignals, and provides CPU-adjustable gain stages. The N-20PA CPU measuresthe sensor’s analog outputs, continually controls the signal gain, and calculatesSpO2 and pulse rate.
The N-20PA is automatically calibrated each time it is switched on, andwhenever a new sensor is connected; it sets sensor-specific calibrationcoefficients by reading a calibration resistor in the sensor. Also, the intensity ofthe sensor’s light sources are adjusted automatically to compensate fordifferences in tissue thickness and darkness.
Section 1: Introduction
1-2
Standard user controls consist of a measure button and a check-battery button.The measure button signals the power control circuit to switch on the powersupply. The power supply then provides regulated power to the unit. Once poweris on, both the measure and check battery buttons are read by the CPU for usercommands.
The N-20PA printer provides a hard copy of acquired patient measurements.The printer circuit includes three user control buttons: ON (on/off), ADV(advance), and D/D (day/date). In addition, an ambient temperature sensor isused with the battery voltage input to control printout quality.
2-1
SECTION 2: ROUTINE MAINTENANCE
2.1 Overview
2.2 Cleaning
2.3 Periodic Safety and Functional Checks
2.4 Batteries
2.1 OVERVIEW
The N-20PA requires no routine maintenance, routine service, or calibration. Ifservice is necessary, contact qualified service personnel or your localMallinckrodt representative. Use only Mallinckrodt-approved test equipmentwhen running a performance test on the N-20PA. The user's institution, local ornational agencies, or both may also require testing.
2.2 CLEANING
Dampen a cloth with a commercial, nonabrasive cleaner, and lightly wipe thesurfaces of the N-20PA. Do not spray or pour liquid on the instrument oraccessories. Do not allow liquid to contact connectors, switches, or openings inthe chassis.
2.3 PERIODIC SAFETY AND FUNCTIONAL CHECKS
The following checks should be performed at least every 2 years by a qualifiedservice technician.
Inspect the exterior of the N-20PA for damage.
Inspect safety labels for legibility. If the labels are not legible, contact MallinckrodtTechnical Services Department or your local Mallinckrodt representative.
2.4 BATTERY
When the N-20PA is going to be stored for 3 months or more, remove the batteryprior to storage. To replace or remove the battery, refer to Section 5,Disassembly Guide.
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3-1
SECTION 3: PERFORMANCE VERIFICATION
3.1 Introduction
3.2 Required Tools and Equipment
3.3 Performance Tests
3.1 INTRODUCTION
This section describes performance verification and safety testing for the NellcorN-20PA pulse oximeter (monitor) and all options, following troubleshooting andrepairs.
The tests can be performed without removing the monitor cover. All tests exceptBattery Operation must be performed before the monitor is returned to the user.
If the monitor fails to perform as specified in any test, repairs must correct thediscrepancy before the monitor is returned to the user.
The N-20PA is powered by alkaline batteries. The N-20PA design includesbuilt-in electrical isolation; no ground resistance or current leakage testing isrequired. In addition, the N-20PA requires no calibration.
3.2 REQUIRED TOOLS AND EQUIPMENT
Durasensor Nellcor DS-100A
Oxisensor II Nellcor D-25
Tester, Pulse Oximeter Nellcor SRC-2 or SRC-1
Variable DC power supply; 1 amp supply, voltage range 0-6 VDC
3.3 PERFORMANCE TESTS
The procedures required to verify correct monitor performance are listed below:
3.3.1 Battery Performance
3.3.2 Power-Up Performance
3.3.3 Hardware and Software Tests
3.3.4 Backlight Test
3.3.5 Low Battery Test
3.3.6 Printer Test
The N-20PA will operate in diagnostic mode in conjunction with the Nellcorpulse oximetry tester, model SRC-2 or SRC-1, to test instrument performance.The SRC-2 plugs into the DB-9 sensor connector and uses the instrument’spower supply and diagnostic software to test the display and the operation of theinstrument. Mallinckrodt recommends routine performance testing at 1-yearintervals. Refer to the SRC-2 operator’s manual for details on performancetesting with the SRC-2.
Performance Verification
3-2
To enter the diagnostic mode, connect the SRC-2 to the N-20PA while theoximeter is off; then, turn the oximeter on. While in the diagnostic mode, a “d”is displayed in the leftmost segment of the display. Note: No alarms sound whilein the diagnostic mode. Note also that, if the SRC-2 is disconnected while theN-20PA is in diagnostic mode, the N-20PA shuts off automatically.
3.3.1 Battery Performance
This test is provided to verify that the monitor will operate for the periodspecified.
The monitor is specified to operate on battery power as follows:
N-20/PA (with printer) 32 hours with Alkaline batteries.
This test requires a new set of batteries. Note that the batteries must be replacedafter the test.
1. Connect the Nellcor SRC-2 pulse oximeter tester to the monitor.
2. Set the switches on the SRC-2 as follows:
Switch Setting
RATE 38
LIGHT LOW
MODULATION LOW
RCAL/MODE RCAL 63/LOCAL
3. Momentarily press the MEASURE button, and then verify the followingpower-up sequence:
a. All indicators--OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS--light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lit.
Software versions may vary depending on the date of manufacture.
The N-20PA will display the letters “PA” in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION display momentarily indicates the letters”tSt” and the monitor sounds a single tone. The other displays are not lit.“tSt” verifies that the monitor recognizes that a tester is connected.
d. The OXYGEN SATURATION and PULSE RATE displays indicate“0,” the PULSE SEARCH indicator is flashing, and the PULSE BARwill start to register the simulated pulse.
e. After a few beats, a pulse tone will be heard, and the PULSE SEARCHindicator will turn off. The OXYGEN SATURATION display indicatesbetween 79 and 83 and the PULSE RATE display indicates between 37and 39.
The N-20PA will indicate a “d” in the most significant digit (MSD) ofthe OXYGEN SATURATION display when the SRC-2 is connected.
Performance Verification
3-3
4. The monitor must operate for at least 37 hours with no printer activity.
5. Verify that the LOW BATTERY indicator lights sometime after 35 hours ofoperation.
6. Verify that the LOW BATTERY indicator starts flashing after 36 hours ofoperation.
7. Verify that the monitor turns off approximately 1 hour after the LOWBATTERY indicator starts flashing.
8. Allow the monitor to continue operation until power-down due to lowbattery.
3.3.2 Power-up Performance
Monitors with the same software must demonstrate identical startup routines.
The power-up tests verify the following monitor functions:
3.3.2.1 Power-On Self-Test
3.3.2.2 Adult Defaults and Alarm Limit Ranges
3.3.2.3 Neonate Defaults and Alarm Limit Ranges
3.3.2.1 Power-On Self-Test
1. Place a new set of batteries in the monitor.
2. Do not connect a sensor or SRC-2 to the monitor.
3. Momentarily press the MEASURE button, and verify the following power-up sequence:
a. All indicators--OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS--light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3 -digit software version. The other displays are not lit.
Note: Software versions may vary depending on the manufacture date.
Note: The N-20PA will display the letters “PA” in the PULSE RATE displaywhile the software version is being dispalyed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION and PULSE RATE display dashes “-” ineach window, the monitor sounds a single tone, and the PULSESEARCH indicator is flashing. The other displays are not lit.
4. Verify that the monitor automatically turns off after 60 seconds.
Change the SRC-2 to the switch configurations shown below, and verify monitoroperation using the chart shown below.
Performance Verification
3-4
SRC-2 Settings Monitor Indications
RATE LIGHT MODULATION SpO2 PR
112 HIGH1 HIGH 81+ 2 112+ 2% (110 - 114)
201 LOW LOW 81+ 2 201+ 3% (195 - 207)
201 LOW HIGH 81+ 2 201+ 3% (195 - 207)
3.3.2.2 Adult Defaults and Alarm Limit Ranges
The following procedure will allow verification of the monitor’s adult factorydefaults, adjusting those defaults, and automatic reset to factory defaults.
1. Place a new set of batteries in the monitor.
2. Connect the DS-100A sensor to the monitor and place the sensor on a livesubject.
3. Press the MEASURE button, and verify the following power-up sequence:
a. All indicators--OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS--light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lit.
Note: Software versions may vary depending on the date of manufacture.
Note: The monitor will display the letters “PA” in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION and PULSE RATE display “0” in eachwindow, the monitor sounds a single tone, and the PULSE SEARCHindicator is lit. The other displays are not lit.
d. The monitor will begin to track the pulse and after a few beats willdisplay the subject’s Oxygen Saturation and Pulse Rate.
If the subject’s OXYGEN SATURATION is below 91, select anothersubject to facilitate the test procedure as written.
4. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the “dashes” are flashing. The “H”indicates that the High Alarm Limits can be set. The “dashes” in the SpO2display indicate that the present setting is the Adult Default of 100% andcannot be increased.
Performance Verification
3-5
SpO2 %
/ min
- +
5. Press the PRINTER ON button and reduce the High Saturation Alarm limitbelow the live subject’s value; typically 90 will be sufficient.
6. Momentarily press the DAY/DATE button and verify that the “90” in theSpO2 display stops flashing and the “170” starts flashing.
7. Press the PRINTER PAPER ADVANCE button and increase the High RateAlarm limit to 190.
8. Momentarily press the DAY/DATE button; then verify that the followingdisplay is shown and that the “85” is flashing.
SpO2 %
/ min
- +
9. Press the PRINTER ON button, and reduce the Low Saturation Alarm limitto 80.
10. Momentarily press the DAY/DATA button, and verify that the “80” in theSpO2 display stops flashing and the “40” starts flashing.
11. Press the PRINTER ON button, and reduce the Low Rate Alarm limit to 30.
12. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the subject’ssaturation and pulse rate.
13. Verify that the monitor begins to alarm and that the SpO2 reading begins toflash.
14. Momentarily press the BATTERY TEST button, and verify that the alarmremains silent for 2 minutes and that the SpO2 reading continues to flash.
Note: The alarm may be silenced as necessary for remainder of the test.
Performance Verification
3-6
15. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the “90” is flashing.
SpO2 %
/ min
- +
16. Momentarily press the DAY/DATE button and verify that the “90” in theSpO2 display stops flashing and that the “190” Rate Default starts flashing.
17. Momentarily press the DAY/DATE button and verify that the followingdisplay is shown and that the “80 “ is flashing.
SpO2 %
/ min
- +
18. Momentarily press the DAY/DATE button and verify that the “80” in theSpO2 display stops flashing and that the “30” in the Rate Display startsflashing.
19. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the live subject’ssaturation and pulse rate.
20. Press the MEASURE button until the monitor turns off.
Performance Verification
3-7
21. Press the MEASURE button, and verify the following power-up sequence:
a. All indicators--OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS --light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lighted.
Note: Software versions may vary depending on the type of monitor and the dateof manufacture.
The monitor will display the letters PA in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION and PULSE RATE displays “0” in eachwindow, the monitor sounds a single tone and the PULSE SEARCHindicator is flashing. The other displays are not lit.
d. The monitor will begin to track the pulse and after a few beats willdisplay the subject’s Oxygen Saturation and Pulse Rate.
22. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the dashes (“-“) are flashing. Thisindicates the monitor has returned to the factory default settings.
SpO2 %
/ min
- +
23. Momentarily press the DAY/DATE button and verify that the dashes (“-“) inthe SpO2 display stop flashing and that the “170” Rate Default startsflashing.
24. Momentarily press the DAY/DATE button and verify that the followingdisplay is shown and that the “85” is flashing.
Performance Verification
3-8
SpO2 %
/ min
- +
25. Momentarily press the DAY/DATA button and verify that the “85” in theSpO2 display stops flashing and that the “40” Rate Default starts flashing.
26. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the live subject’ssaturation and pulse rate.
27. Press the MEASURE button until the monitor turns off.
3.3.2.3 Neonate Defaults and Alarm Limit Ranges
The following procedure will allow verification of the monitor NEONATALfactory defaults, adjusting those defaults, and automatic reset to factory Adultdefaults.
1. Place a set of batteries in the monitor. Verify that batteries are new.
2. Connect the DS-100A sensor to the monitor and place the sensor on alive subject (adult subject is OK for this procedure).
3. Press and hold the BATTERY TEST button and press the MEASUREbutton for at least 5 seconds, and then verify the following power-upsequence:
a. All indicators—OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS--light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lit.
Note: Software versions may vary depending on the date of manufacture.
The monitor will display the letters PA in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION and PULSE RATE displays “0” in eachwindow, the monitor sounds a single tone, and the PULSE SEARCHindicator is lit. The other displays are not lit.
An “n” will be displayed in the Most Significant Digit (MSD) of theSpO2 display, indicating the Neonatal mode.
Performance Verification
3-9
d. The monitor will begin to track the pulse and after a few beats willdisplay the subject’s Oxygen Saturation and Pulse Rate.
4. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the “95” is flashing. The “H” indicatesthat the High Saturation Alarm Limit can be set.
SpO2 %
/ min
- +
5. Press the PRINTER ON button and reduce the High Saturation Alarm limitto 90.
6. Momentarily press the DAY/DATE button and verify that the “90” in theSpO2 display stops flashing and that the “190” starts flashing.
7. Press the PRINTER PAPER ADVANCE button and increase the High RateAlarm limit to 205.
8. Momentarily press the DAY/DATE button to verify that the followingdisplay is shown and that the “80” is flashing.
SpO2 %
/ min
- +
9. Press the PRINTER ON button and reduce the Low Saturation Alarm limitto 70.
10. Momentarily press the DAY/DATE button and verify that the “70” in theSpO2 display stops flashing and that the “90” starts flashing.
11. Press the PRINTER ON button and reduce the Low Rate Alarm limit to 80.
Performance Verification
3-10
12. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the live subject’ssaturation and pulse rate.
13. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the “90” is flashing.
SpO2 %
/ min
- +
14. Momentarily press the DAY/DATE button and verify that the “90” in theSpO2 display stops flashing and that the “205” Rate Default starts flashing.
15. Momentarily press the DAY/DATE button and verify that the followingdisplay is shown and that the “70 “ is flashing.
SpO2 %
/ min
- +
16. Momentarily press the DAY/DATE button and verify that the “70” in theSpO2 display stops flashing and that the “80” in the Rate Display startsflashing.
17. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the live subject’ssaturation and pulse rate.
18. Verify that the monitor begins to alarm and that the number representing thelive subject’s saturation and pulse rate begins to flash.
Performance Verification
3-11
19. Momentarily press the BATTERY TEST button and verify that the alarmremains silent for 2 minutes and that the number representing the livesubject’s saturation and pulse rate continues to flash.
The alarm may be silenced as necessary for remainder of the test.
20. Press the MEASURE button until the monitor turns off.
21. Press the MEASURE button, and verify the following power-up sequence:
a. All indicators--OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS--light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lit.
Note: Software versions may vary depending on the date of manufacture.
The monitor will display the letters PA in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION and PULSE RATE display dashes “0” ineach window, the monitor sounds a single tone, and the PULSESEARCH indicator is lit. The other displays are not lit.
d. The monitor will begin to track the pulse and after a few beats willdisplay the subject’s Oxygen Saturation and Pulse Rate.
22. Press and hold the BATTERY CHECK button and then momentarily pressthe DAY/DATE (D/D) button on the top of the monitor. Verify that thefollowing display is shown and that the “dashes” are flashing. This indicatesthe monitor has returned to the factory default settings.
SpO2 %
/ min
- +
23. Momentarily press the DAY/DATE button and verify that the “dashes” inthe SpO2 display stop flashing and that the “170” Rate Default startsflashing.
24. Momentarily press the DAY/DATE button, and verify that the followingdisplay is shown and that the “85” is flashing.
Performance Verification
3-12
SpO2 %
/ min
- +
25. Momentarily press the DAY/DATA button and verify that the “85” in theSpO2 display stops flashing and that the “40” Rate Default starts flashing.
26. Momentarily press the DAY/DATE button and verify that the monitorreturns to the normal monitoring display and indicates the live subject’ssaturation and pulse rate.
27. Press the MEASURE button until the monitor turns off.
3.3.3 Hardware and Software Tests
Hardware and software tests include the following:
3.3.3.1 Operation with a Pulse Oximeter Tester
3.3.3.2 Normal Operation
3.3.3.1 Operation with a Pulse Oximeter Tester
1. Connect the Nellcor SRC-2 pulse oximeter tester to the monitor.
2. Set the switches on the SRC-2 as follows:
Switch Setting
RATE 38
LIGHT LOW
MODULATION LOW
RCAL/MODE RCAL 63/LOCAL
3. Momentarily press the MEASURE button, and verify the following power-up sequence:
a. All indicators—OXYGEN SATURATION, PULSE RATE, PULSESEARCH, LOW BATTERY, and the PULSE BARS—light for a fewseconds. Verify that the OXYGEN SATURATION and PULSE RATEdisplays indicate "888."
Performance Verification
3-13
b. The OXYGEN SATURATION display momentarily indicates themonitor 3-digit software version. The other displays are not lit.
Note: Software versions may vary depending on the date of manufacture.
The N-20PA will display the letters “PA” in the PULSE RATE displaywhile the software version is being displayed in the OXYGENSATURATION display.
c. The OXYGEN SATURATION display momentarily indicates the letters”tSt” and the monitor sounds a single tone. The other displays are not lit.“tSt” verifies that the monitor recognizes that a tester is connected.
d. The OXYGEN SATURATION and PULSE RATE displays indicate“0,” the PULSE SEARCH indicator is flashing, and the PULSE BARwill start to register the simulated pulse.
e. After a few beats a pulse tone will be heard, and the PULSE SEARCHindicator will turn off. The OXYGEN SATURATION display indicatesbetween 79 and 83 and the PULSE RATE display indicates between 37and 39.
The N-20PA will indicate a “d” in the most significant digit (MSD) ofthe OXYGEN SATURATION display when the SRC-2 is connected.
3.3.3.2 Normal Operation
These tests are an overall qualitative check of the system and requiresconnecting a live subject to the monitor.
1. Connect a DS-100A Sensor to monitor.
2. Place the DS-100A Sensor on the subject as recommended in the N-20PA Operator's Manual.
3. Press the MEASUREMENT button to turn on the monitor.
4. The monitor should stabilize on the subject's physiological signal inabout 10 to 15 seconds. Verify that the saturation value and pulse ratesare acceptable
3.3.4 Backlight Test
The electroluminescent backlight illuminates the display in three sections:
1. The main section, that is, the Oxygen Saturation and Pulse Rate displayfields, and the 14-segment pulse rate amplitude indicator;
2. The Low Battery indicator, and
3. Pulse Search indicators each have their own backlight. Each backlightflashes once during Power-On Self Test.
The ambient light detector is located underneath a small circular window in thetop right corner of the N-20PA display. Under low light conditions, the mainsection backlight is switched on. If a Low Battery and Pulse Search indicator islit, those individual backlights are also lit.
Performance Verification
3-14
To test for proper operation of the display backlight, observe the N-20PA in adarkened room. If any backlight section is not working correctly, contactMallinckrodt’s Technical Services Department or your local Mallinckrodtrepresentative for assistance.
3.3.5 Low Battery Test
The N-20PA CPU monitors the battery voltage level and alerts the user via theLow Battery indicator when voltage is getting low. To test the proper functionof the Low Battery indicator, connect the N-20PA to an external variable DCpower supply.
Battery voltage levels described in this section are accurate; however, slightvariations may exist due to differences between batteries of differentmanufacturers. To that point, the N-20PA operates normally at voltages above4.0 VDC.
When the battery voltage drops below 4.05 VDC, the Low Battery indicator islit, and the two lowest segments of the battery level meter are lit (number ofsegments lit is dependent upon battery strength) when the battery-check button ispressed. When the voltage level drops below 4 VDC, the N-20PA continues todisplay Oxygen Saturation and Pulse Rate values, but the printer no longeroperates; otherwise, the N-20PA operates normally.
Battery voltage levels below 3.5 VDC cause the Low Battery indicator to beginflashing. When the battery-check button is pressed only the lowest segment ofthe Low Battery indicator will illuminate.
When the battery voltage level drops below 3.3 VDC, the N-20PA turns itselfoff.
Caution: If a sensor is attached, remove it prior to running the followingtest.
To test for proper function of the Low Battery indicator:
1. Switch off the N-20PA; open the battery door and remove the batteries.
2. Set the power supply voltage to 5 VDC, and connect the supply to thebattery contacts of the N-20PA.
Note: Ensure that polarity is correct.
3. Switch on the N-20PA; verify complete Power-On Self Test (the N-20PAshould operate normally).
4. Decrease the power supply voltage to 4.0 VDC or slightly below. The LowBattery indicator should illuminate and the lowest two segments of thebattery level meter should illuminate and printer operation should cease.
5. Decrease the power supply voltage to 3.5 VDC or slightly below. Thenpress the battery-check button; the Low Battery indicator should begin toflash and only the lowest segment of the battery level meter shouldilluminate.
6. Decrease the power supply voltage to below 3.2 VDC. The N-20PA shouldturn itself off immediately. Pressing the measure button should not turn theunit back on.
Performance Verification
3-15
The Low Battery indicator test is now complete.
3.3.6 Printer Test
The SRC-2 tester can be used to test the operation of the N-20PA printer and theprinter’s user-control buttons. When an SRC-2 is plugged into the DB-9connector, the N-20PA acknowledges any button press with an immediate beepand the following display codes:
Button Press Display
On/Off 9O
battery check bAt
ON On
ADV Ad
D/D dd
combinations Err
1. Momentarily click the On/Off button: “9O” appears in (or shuts off) theOxygen Saturation display.
2. Press the battery-check button: “bAt” appears in the Oxygen Saturationdisplay.
3. Press the printer ON button: “On” appears in the Oxygen Saturation display.A printer test pattern prints out; the following is an approximate example ofthe test pattern:
Examine the test pattern to verify that all dots print with a uniform darkness.Overall printout darkness can be adjusted; to adjust printer darkness, seeparagraph 0. If printout darkness is either irregular or dots are missing, contactMallinckrodt’s Technical Services Department or your local Mallinckrodtrepresentative for assistance.
4. Press the printer ADV button: “Ad” appears in the Oxygen Saturationdisplay. The paper advances one line for each button press.
5. Press the printer D/D button: “dd” appears in the Oxygen Saturation display.
The SRC-2 printer test is now completed.
Performance Verification
3-16
TEST RESULTS
Model: N-20PA Serial:_____________________________
Date:___________Customer Name:________________________________
Test # Description Pass Fail
3.3.1 Battery Performance ____ ____
3.3.2 Power-Up Performance ____ ____
3.3.2.1 Power-Up Self-Test ____ ____
3.3.2.2 Adult Defaults and Alarm Limit Ranges ____ ____
3.3.2.3 Neonate Defaults and Alarm Limit Ranges ____ ____
3.3.3 Hardware and Software Tests ____ ____
3.3.3.1 Operation with a Pulse Oximeter Tester ____ ____
3.3.3.2 Normal Operation ____ ____
3.3.4 Backlight Test ____ ____
3.3.5 Low Battery Test ____ ____
3.3.6 Printer Test ____ ____
I certify that the monitor listed in this form has successfully passed all of these tests.
Technician:_________________________________________________Date:____________
I certify that the above signed technician has performed the tests listed on this form and the monitorperforms satisfactorily.
Support CenterManager:___________________________________________________Date:____________
4-1
SECTION 4: TROUBLESHOOTING4.1 Introduction4.2 How to Use This Section4.3 Who Should Perform Repairs4.4 Replacement Level Supported4.5 Obtaining Replacement Parts4.6 Troubleshooting Guide
4.1 INTRODUCTION
This section explains how to identify and correct monitor difficulties andprovides procedures for common service-related activities, such as batteryreplacement, clearing paper jams, and adjusting printer darkness.
4.2 HOW TO USE THIS SECTION
Use this section in conjunction with Section 3, Performance Verification, andSection 6, Spare Parts. To remove and replace a part you suspect is defective,follow the instructions in Section 5, Disassembly Guide. The functional circuitanalysis, located in the Technical Supplement at the end of this manual, offersinformation on how the device functions, as well as part locator diagrams anddetailed schematic diagrams.
4.3 WHO SHOULD PERFORM REPAIRS
Only qualified service personnel should open the device housing, remove andreplace components, or make adjustments. If your medical facility does not havequalified service personnel, contact Mallinckrodt Technical Services.
4.4 REPLACEMENT LEVEL SUPPORTED
The replacement level supported for this product is to the printed circuit board(PCB) and major subassembly level. Once you isolate a suspected PCB, replacethe PCB with a known good PCB. Check to see that the trouble symptomdisappears and the device passes all performance tests. If the trouble symptompersists, swap the replacement PCB and the suspected malfunctioning PCB (theoriginal PCB that was installed when you started troubleshooting) and continuetroubleshooting as directed.
4.5 OBTAINING REPLACEMENT PARTS
Mallinckrodt Technical Services provides technical assistance information andreplacement parts. To obtain replacement parts, contact Mallinckrodt. Refer toparts by the part names and part numbers listed in Section 6, Spare Parts.
4.6 TROUBLESHOOTING GUIDE
Table 4-1 this section discusses potential symptoms, possible causes, and actionsfor their resolution. Should this troubleshooting guide fail to address thesymptoms evident in a particular N-20PA, please contact Mallinckrodt TechnicalServices or your local Mallinckrodt representative for assistance.
Troubleshooting
4-2
If the N-20PA does not perform as expected, the problem may be related to thefollowing:
• Incorrect sensor placement.
• Depending on concentration, indocyanine green, methylene blue, and otherintravascular dyes may affect the accuracy of a measurement.
• These instruments are calibrated to read oxygen saturation of functionalarterial hemoglobin (saturation of hemoglobin functionally capable oftransporting oxygen in the arteries). Significant levels of dysfunctionalhemoglobins such as carboxyhemoglobin or methemoglobin may affect theaccuracy of a measurement.
If the electronics or display functions, or both, require testing, refer to thePerformance Verification section.
Table 4-1 : Troubleshooting the N-20PA
Symptom Possible Cause RecommendedAction
No response to On/Offbutton.
1. Battery access door maynot be properly latched.
2. Batteries may bedischarged.
3. Batteries may beincorrectly installed.
4. Batteries may not bemaking proper electricalcontact.
5. Fuse F1 on the auxiliaryPCB may be open.
6. Dust may haveaccumulated under On/Offbutton causing loss ofelectrical contact.
1. Check access door andensure that it is properlylatched.
2. Exchange batteries for anew set.
3. Ensure that batteries areoriented according to thepolarity indicator.
4. Inspect battery contactsfor deformity; clean contactsto remove oxidization.
5. See Section 4.7.5,Replacing Fuses.
6. Clean contact points underOn/Off button (see Section5.2.1, N-20PA DisassemblyProcedures).
Pulse Search indicatorappears for more than5-10 seconds.
1. Sensor may be improperlypositioned.
2. Incorrect sensor may be inuse.
3. Perfusion may be too low.
4. Foreign material on the
1. Ensure that the sensor iscorrectly applied (see sensorDirections for Use).
2. See sensor Directions for Useto ensure that the patient’sweight and sensor applicationare correct. Test the sensor onanother person to verify properoperation.
3. Check patient status. Test theinstrument on someone else, ortry another type of sensor. TheN-20PA will not make ameasurement if perfusion isinadequate.
4. Clean the test area and ensure
Troubleshooting
4-3
sensor LEDs or photodetectormay be affecting performance.
5. Patient motion may beinterfering with the instrument’sability to find a pulse pattern.
6. Environmental motion maybe interfering with theinstrument’s ability to track apulse.
7. The sensor may be too tight,there may be excessiveillumination (for example, asurgical or bilirubin lamp ordirect sunlight), or the sensormay be placed on an extremitywith a blood pressure cuff,arterial catheter, or intravascularline; Mallinckrodt does notrecommend using a sensor onthe same limb as these threedevices.
8. The DB-9 sensor connectoron the N-20PA may be broken.
that nothing blocks the sensorsite.
5-7. If possible, ask the patientto remain still. Verify that thesensor is securely applied andreplace it if necessary, move itto a new site, or use a sensorthat tolerates patient movement,such as an appropriate adhesivesensor.
8. Replace the DB-9 connector.
Pulse Search indicatorappears after successfulmeasurements havebeen made.
1. Patient perfusion may betoo low.
2. Patient motion may beinterfering with theinstrument’s ability to find apulse pattern.
3. Environmental motionmay be interfering with theinstrument’s ability to track apulse.
4. The sensor may be tootight, there may be excessiveillumination (for example, asurgical or bilirubin lamp ordirect sunlight), or the sensormay be placed on anextremity with a bloodpressure cuff, arterialcatheter, or intravascularline; do not use the sensor onthe same limb as these threedevices.
1. Check patient status. Testthe instrument on someoneelse, or try another type ofsensor. The N-20PA will notmake a measurement ifperfusion is inadequate.
2-4.If possible, ask thepatient to remain still.Verify that the sensor issecurely applied and replaceit if necessary, move it to anew site, or use a sensor thattolerates patient movement,such as an appropriateadhesive.
Troubleshooting
4-4
Dashes (- - -) appear inthe display.
The sensor is not connectedto the instrument.
Check all sensorconnections; try substitutinganother sensor. Check allextension cables. If anextension cable is in use,remove it and plug the sensordirectly into the instrument.
Pr Err is displayedduring the POST.
The printer is not operational(however, the N-20PAcontinues to obtain patientmeasurements) due to paperjam or print head not in thehome position.
Check to see if the paper isjammed. Examine the printhead and ensure that it hasreturned to the homeposition. Turn the printer off,then on again.
Err followed by anumber appears on thedisplay.
See Section 4.7.8 for errorcodes.
Record the number that isdisplayed.
Time or date isincorrect.
The real-time clock (RTC)battery may be exhausted.
Replace the RTC battery (seeSection 4.7.4).
Resent the time and date (seeSection 4.7.3).
Printer fails to operate. Fuse F2 on the auxiliaryPCB may be open.
Batteries may be low.
1. See Section 4.7.5 forinformation about fuses.
2. Replace old batteries withfresh batteries.
Printer paper advancesbut instrument does notprint.
The thermal paper may beimproperly loaded;characters can be printed ononly one side of the thermalpaper roll.
Ensure that the thermal paperis properly loaded; if needed,remove the roll of printerpaper and reload the printerpaper.
Paper mechanism jams.
Note: If a printer paperjam is detected whenthe printer is turned on,Pr Err may appear onthe display.
Switch off the N-20PA. Thencheck to see if the print headis at the home position; if so,attempt to pull the paper outby pulling gently - - do notforce it.
If the print head is not at thehome position, and the papercannot be easily pulled outfrom the printer, then theprinter may need to bedisassembled to remove thepaper jam (see Sections 5.3,N-20PA DisassemblyProcedure, and 4.7.2,Loading/Clearing PrinterPaper).
4.7 Service Procedures
The following service procedures are most likely to be encountered by theservice technician. The PCB designation for a component appears inparentheses; for example, (BT1) or (U15).
Troubleshooting
4-5
4.7.1 Installing Batteries
The N-20PA operates on four 1.5-V alkaline “C” cell batteries. Do not useoff-the-shelf rechargeable batteries; this type of battery can cause the LowBattery indicator to be inaccurate. To install the batteries:
1. Remove the battery access door by pressing the battery compartment accessdoor latch.
2. Install four alkaline “C” cell batteries. Be sure to observe the polarityindicator sticker.
3. Replace the battery cover access door.
4.7.2 Loading/Clearing Printer Paper
The N-20PA uses a thermal paper that can show printed characters on one sideonly. Make sure that the paper roll is correctly installed; always refer to thegraphical instruction label found on the paper roll. To load the paper:
1. Press down and outward on the top of the paper compartment door to removeit.
2. Feed the paper into the paper compartment slot; refer to the graphic label fororientation.
3. Press and hold the ADV button until the end of the paper appears at the paperexit slot.
4. Replace the paper compartment door.
If the paper jams either during the loading process or during printing, proceed asfollows:
1. Remove both the paper door and the printer-head access cover.
2. Firmly grab and pull the paper roll backward—out and away from the printhead—and observe the print head access to determine whether or not thepaper escaped from the jammed position.
3. If paper remains jammed between the printer head and printer, press theADV button; the jammed paper may work its way out. If the paper remainsjammed, and the printer drive does not advance the paper, manually advancethe drive gear on the side of the printer to free the paper.
If these attempts fail to free the jammed paper, remove the printer from the unitto gain full access (see Section 5.3, N-20PA Disassembly Procedure).
4.7.3 Setting Date and Time
The following code letters and numbers appear in both Oxygen Saturation andPulse Rate display fields. The symbol “xx” represents information in theOxygen Saturation display field and “yy” represents information in the PulseRate display field.
1. To set the date and time: Remove any sensor from the instrument.
2. Switch on the N-20PA and allow the unit to run POST.
Troubleshooting
4-6
3. When dashes appear in the Oxygen Saturation and Pulse Rate displays, pressthe D/D (day/date) button once. At this point, the Oxygen Saturation displayshows “txx”, with “t” representing time; “xx” representing hours, and “yy”representing minutes. Note that “xx” (hours) is flashing.
4. Press the ADV (advance) button repeatedly until the correct hour isdisplayed.
5. Press the D/D button once. Note that “yy” (minutes) is now flashing.
6. Press the ADV button repeatedly until the correct minute is displayed.
7. Press the D/D button. At this point, the Oxygen Saturation display shows“dxx”, with “d” representing date; “xx” representing the day and “yy”representing the month. Note that “xx” (day) is flashing.
8. Press the ADV button repeatedly until the correct date is displayed.
9. Press the D/D button once. Note that “yy” (month) is flashing.
10. Press the ADV button repeatedly until the correct month is displayed.
11. Press the D/D button. At this point, the Oxygen Saturation display shows“Yxx,” with “Y” representing “year”. Note that “xx” (year number) isflashing.
12. Press the ADV button repeatedly until the correct year number is displayed.
13. Press the D/D button once. The N-20PA turns itself off immediately.
14. Verify that date and time are now correct by switching on the N-20PA andthen enabling the printer. After the N-20PA executes its POST, the printerprints the header with the correct date and time.
Note: The parenthetic line description is not printed. Button presses areignored whenever the printer is printing.
Note: If in the D/D mode and there is no user interaction (no buttons are beingpressed) for 60 seconds, the N-20PA turns off and any changes made arenot saved.
4.7.4 Replacing the Real-Time Clock (RTC) Battery
The socket for the RTC battery (BT1) is located on the auxiliary PCB. Typicallife of the clock battery is 5 years.
Caution: After replacing an RTC battery, switch the instrument on, thenimmediately switch it off; this action will prevent possible damage to theRTC voltage circuit.
To replace the real-time clock/battery:
1. Disassemble the N-20PA (see Section 4.3, Disassembly Guide).
2. Using a thin flat-head screwdriver, gently pry the RTC battery from itssocket.
3. Insert a new battery into the socket, observing the polarity indication(socket’s clip and battery’s flat side are positive).
4. Reassemble the unit.
5. Switch on the instrument, then immediately switch it off (the RTC voltagecircuit requires this step to prevent possible damage to the unit). Theinstrument is now ready for normal operation.
Troubleshooting
4-7
6. Reset the clock (see paragraph 4.7.3, Setting Date and Time).
4.7.5 Replacing Fuses
Two fuses (F1 and F2) are located on the auxiliary PCB. Fuse F1 may open toprotect the CPU and its associated components from damage if the power supplymalfunctions. Fuse F2 may open to protect the printer from damage due toexcessive voltage if the printer head jams or if it has been physically damaged.Refer to the auxiliary PCB schematic for the locations of F1 and F2.
4.7.6 Replacing the DB-9 Connector
To replace the DB-9 connector:
1. Disassemble the N-20PA (see Section 5); the connector is on the main PCB.
3. Using a low-power soldering iron, unsolder the connector from the PCB andremove it.
Note: Save all Teflon tubing, ferrite blocks, and insulating materials for thereplacement connector.
3. Install ferrite blocks between the plastic lead spacer on the connector and thePCB.
4. Insulate connector pin numbers 2, 3, and 5 with Teflon tubing, and insertinside ferrite block.
5. Add insulating material between each end of ferrite block and the PCB, andsecure with Loctite glue.
6. Solder new connector to the PCB and visually check the PCB for stray dropsof solder before reassembling.
7. Switch on the N-20PA and test the connector with a patient sensor.
4.7.7 Adjusting Printer Darkness
Caution: Adjust the printer darkness setting until the lightest legible printis visible. Setting the print darker than this could reduce printer-head life.
Although the N-20PA is designed to automatically compensate for conditionsthat might influence the quality of the printout, the user may want to adjust theprint darkness. The normal darkness setting is set at the factory; this settingmaximizes both readability and printer head life.
Note: This procedure cannot be performed after a valid pulse is receivedfollowing power-on. Hence, perform this procedure with no sensorattached to the monitor.
To adjust the printer darkness:
1. Switch on the N-20PA.
Troubleshooting
4-8
2. Simultaneously press and hold the ADV and printer ON buttons for 4seconds. If these buttons are not pressed at the same time, two audible beepswill sound and the N-20PA either advances the paper or turns on (or off) theprinter, depending on which button-press is first sensed. If the buttons arepressed at the same time, a single audible beep will sound, Pr SEt isdisplayed, and the printer prints one of the following 6 lines:
PRINTING LIGHTER (10% lighter than normal)
PRINTING LIGHT (5% lighter than normal)
PRINTING NORMAL (normal darkness)
PRINTING DARK (5% darker than normal)
PRINTING DARKER (10% darker than normal)
PRINTING DARKEST (15% darker than normal)
Note: The parenthetic line description is not printed. Button presses areignored whenever the printer is printing.
1. Press the ADV button to change the darkness setting. The printer prints aline with each button press, and the setting increments from lighter todarkest and then wraps back to lighter.
2. Allow the N-20PA to switch off (about 30 seconds). The last printerdarkness setting is remembered when the N-20PA is switched back on.Test this by repeating the procedure and skipping step 3.
4.7.8 Error Codes
If a failure is detected during the Power-On Self-Test or during any performancetest, the error message (Err) appears in the Oxygen Saturation display and a3-digit error code number appears in the Pulse Rate display.
If an error message appears, record the error code number. Match the number tothe description in the following table, and contact Mallinckrodt’s TechnicalServices Department or your local Mallinckrodt representative for assistance.The first digit of the error code is the category.
Internal tests are performed in the order listed in the table. The first errorcondition encountered is the one displayed.
Troubleshooting
4-9
Category 1 — Microprocessor Errors
Errors in the CPU (main PCB). Likely action is replacement of the CPU.
101
102
103
104
105
106–109
110
111
112
113,114
115–117
118
119
120
121
122
123
124
125
126–129
Error in internal RAM register test
Error in zero register test
Error in register contents clearing test
Error in register contents increment test
Error in register contents decrement test
Errors in logical operations test
Error in exchange test
Error in timer tests
Error in window select register test
Errors in stack manipulation test
Errors in CPU flags test
Error in interrupt pending register test
Error in program counter test
Error in CPU serial port test
Error in pulse width modulation register test
Error in A/D register test
Error in addressing modes test
Error in high-speed input register test
Error in content addressable memory test
Errors in arithmetic operations test
Category 2 — RAM Memory Errors
Errors in RAM memory (main PCB). Likely action is replacement of the mainPCB.
201-203 Errors in external RAM test
Category 3 — PROM Errors
Errors in PROM memory (main PCB). Likely action is replacement of thePROM.
301 Error in PROM test
Category 4 — I/O Port Errors
Errors in the CPU internal I/O port (main PCB). Likely action is replacement ofeither the CPU or the main PCB.
401-409 Errors in I/O port test
Category 5 — Reserved
Troubleshooting
4-10
Category 6 — Clock Errors
Failure of the real-time clock (auxiliary PCB), or timing differences between theCPU clock and the real-time clock. Likely action is replacement of the main orauxiliary PCB.
601
602, 603
Failure of real-time clock
Errors in real-time clock
Category 7 — Watchdog-Timer Errors
Error in the watchdog-timer circuit of the CPU (main PCB). Likely action isreplacement of the CPU.
701, 702 Errors in watchdog-timer
Category 8 — Printer Errors
Error in the printer. If a printer error condition occurs, the display reads Pr Err.See the Troubleshooting section for further information on this error.
5-1
SECTION 5: DISASSEMBLY GUIDE5.1 Introduction5.2 Beginning Disassembly5.3 N-20PA Disassembly Procedure
5.1 INTRODUCTION
The device can be disassembled down to all major component parts, including:
• PCBs
• batteries
• cables
• chassis enclosures
Tools required:
• small, Philips-head screwdriver
• small flat-head screwdriver
• needle-nose pliers
• low-power soldering iron
WARNING: Before attempting to open or disassemble the device, turn itoff.
Caution: Observe ESD (electrostatic discharge) precautions when workingwithin the unit.
5.2 BEGINNING DISASSEMBLY
20
34
19
21
Figure 5-1: Sensor Lock, Printer, Paper, and Battery Access Doors
Figure 5-1 shows the how to start the N-20PA disassembly.
Section 5: Disassembly Guide
5-2
1. Remove the battery door (19) and batteries.
2. Remove the sensor lock (34) by lightly pressing in on its ears and pulling outfrom the sensor shroud.
3. Remove the paper door (20), paper roll, and the printer door (21).
5.2.1 Removing the Covers
16
18
27
26
15
31
30
Figure 5-2: N-20PA Covers with the PCB and Display Assembly
Figure 5-2 shows how to remove the N-20PA cover and display assembly.
1. Remove screw cap (30) and loosen the captive screw (31) that secures therear battery cover (15).
Section 5: Disassembly Guide
5-3
2. Separate the front cover (16) from the rear battery cover by wedging a thinflat-head screw driver between the covers at the base of the instrument andslowly prying them apart.
Note: The covers are hinged at the top end in a different way; do not attempt toseparate the covers using this technique at the top of the instrument.Once the covers are separated at the bottom end, lift away the bottomend of the front cover first, allowing the tabs at the top end to act as ahinge.
5.2.2 Removing the PCBs and Display Assembly
18
Tab #4
Tab #1
Tab #2
Tab #3
Detail A
Detail B
26
13
12
11
27
6Flex #1
Flex #3Flex #2
5
Figure 5-3: Main, Auxiliary, and Display PCB Assembly
Figure 5-3 shows how to remove the PCB assemblies.
1. Remove the On/Off button (6) from the main PCB.
2. Remove the entire PCB/Taliq display assembly from the rear battery coverby tilting opposite the battery-check button (5).
3. Release connectors (11, 12, and 13) on the auxiliary PCB (26) and removethe three flex display circuits.
4. Separate the auxiliary PCB from the main PCB (27) by pulling the PCBheaders apart at the base.
5. Remove the display assembly (18) from the main PCB by unsoldering thefour tabs that are physically bent around the main PCB. These tabs are bentto ensure contact with the ground plane of the main PCB.
6. Using long-nose pliers, remove the metal shroud by untwisting the four tabs(see Detail A and B).
Section 5: Disassembly Guide
5-4
5.3 DISASSEMBLYING THE PRINTER/FLEX CIRCUIT ASSEMBLY
24
28
37
7
29
32
4
Figure 5-4: Printer and Flex Circuit Assembly
Figure 5-4 shows how to disassemble the printer and flex circuitry.
1. Remove the printer button stiffener (37).
2. Disconnect the two flex-circuit headers of the printer (29) from theconnectors on the printer flex circuit (28) by slowly pulling them outwardfrom side to side at alternating ends of the connectors.
3. Remove the printer button strip (7) from the printer flex-circuit.
4. Remove the printer flex-circuit insulator (24).
5. Remove the printer hold-down bracket (4) from the back cover by removingthe Phillips screw (32).
6. Press the printer hold-down bracket into the back cover and remove theprinter.
6-1
SECTION 6: SPARE PARTS6.1 Introduction6.2 Spare Parts List
6.1 INTRODUCTION
Spare parts, along with corresponding part numbers, are shown below. To orderreplacement parts, contact Mallinckrodt’s Technical Services Department andorder by part number.
6.2 SPARE PARTS LIST
Item Designator Description P/N
1 SW1 Battery switch (auxiliary PCB) 630106
2 BT1 Battery holder (auxiliary PCB) 901582
3 BT1 Battery, lithium (auxiliary PCB) 640112
4 Bracket, printer, hold-down 023133
5 Button, battery-check 023301
6 S2 Button, measure 022948
Button, measure (European version) 026386
7 Buttons, printer, strip 022947
Buttons, printer, strip (European version) 026387
8 L1, L2 Coil, 120 µH SMT (auxiliary PCB) 691238
9 Connector shield, DB-9 023467
10 P1 Connector, DB-9 463103
11 JP17, JP18 Connector, pin header 10x2, low profile(auxiliary PCB)
491244
12 JP5 Connector, ZIF, flex, 7-pin (auxiliary PCB) 491242
13 JP9 Connector, ZIF, flex, 22-pin (auxiliary PCB) 491250
14 JP2, JP3 Connector, ZIF, flex, 32-pin (auxiliary PCB) 491243
15 Cover, battery, rear (non-printer model) 022929
Cover, battery, rear (printer model) 026339
16 Cover, front, with gasket assembly 022921
17 D8 Diode, photo, 8440 (main PCB) 591017
18 Display, Taliq, analog shield assembly 024466
Display, Taliq, analog shield assembly(European version)
026765
19 Door, battery 022924
20 Door, paper. 022938
Spare Parts
6-2
Item Designator Description P/N
21 Door, printer 026338
22 F2 Fuse, micro, 1 amp (auxiliary PCB) 691236
23 F1 Fuse, micro, 1.5 amp (auxiliary PCB) 691239
24 Insulator, printer 026139
Item Designator Description P/N
25 Nut, keps, SS, 4-40 851101
26 PCB, auxiliary 024472
27 PCB, main 024468
28 Printer flex circuit 024464
29 Printer 024462
30 Screw cap 023451
31 Screw, captive 891324
32 Screw, Phillips, 4-40 x 1/4 801025
33 Screw, plastite 871031
34 Sensor lock 022943
35 Sensor shroud 022944
36 Spacer 023452
37 Stiffener, printer button 023131
38 Tape, foam (.88” x .38”) 023300
39 BZ1 Transducer, audio, piezo ceramic 691230
7-1
SECTION 7: PACKING FOR SHIPMENT7.1 General Instructions7.2 Repacking in Original Carton7.3 Repacking in a Different Carton
Should you need to ship the N-20PA monitor for any reason, follow theinstructions in this section.
7.1 GENERAL INSTRUCTIONS
Pack the monitor carefully. Failure to follow the instructions in this section mayresult in loss or damage not covered by the Mallinckrodt warranty. If theoriginal shipping carton is not available, use another suitable carton or callMallinckrodt Technical Services to obtain a shipping carton.
Prior to shipping the device, contact Mallinckrodt Technical Services for areturned goods authorization (RGA) number. Mark the shipping carton and anyshipping forms with the RGA number.
7.2 REPACKING IN ORIGINAL CARTON
If available, use the original carton and packing materials. Pack the monitor asfollows:
1. Place the monitor and, if necessary, accessory items in original packaging.
2. Place in shipping carton and seal carton with packaging tape.
3. Label carton with shipping address, return address, and RGA number.
7.3 REPACKING IN A DIFFERENT CARTON
If the original carton is not available:
1. Place the monitor in plastic bag.
2. Locate a corrugated cardboard shipping carton with at least 200 pounds persquare inch (psi) bursting strength.
3. Fill the bottom of the carton with at least two inches of packing material.
4. Place the bagged unit on the layer of packing material and fill the boxcompletely with packing material.
5. Seal the carton with packing tape.
6. Label carton with shipping address, return address, and RGA number.
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8-1
SECTION 8: SPECIFICATIONS8.1 Performance8.2 Alarms8.3 Electrical8.4 Environmental8.5 Physical
8.1 PERFORMANCE
8.1.1 Range
Saturation
0–100%
Pulse Rate20–250 beats per minute (bpm)
8.1.2 Accuracy
SpO21
Adults 70–100% ± 2 digits2
0–69% unspecified
Neonates 70–95% ± 2 digits2
0–69% unspecified
Pulse rate20–250 bpm ± 3 bpm2
8.2 ALARMS
8.2.1 Alarm Limit Range
Saturation20–100%
Pulse Rate30–250 bpm
1 The reference for accuracy testing is an N-200 oximeter and D-25 sensors that have been validated inhuman blood studies against an Instrumentation Laboratories CO-Oximeter. Adult accuracy specificationis based on testing with D-25 sensors; neonatal accuracy specification is based on testing with N-25sensors. For specifications with other NELLCOR sensors, see the sensor Directions for Use.2 This variation equals one standard deviation (SD). Plus or minus one SD encompasses 68% of thepopulation.
Section 8: Specifications
8-2
8.2.2 Factory Default Alarm Settings
Adult Neonate
SpO2 Upper Limit: 100% 95%
SpO2 Lower Limit: 85% 80%
PR Upper Limit: 170 bpm 190 bpm
PR Lower Limit: 40 bpm 90 bpm
8.3 ELECTRICAL
8.3.1 Battery
TypeFour alkaline “C” size batteries
Battery CapacityTypically 32 hours with four alkaline “C” size batteries1
8.3.2 Instrument
Power Requirements4–6 V, supplied by battery only
Patient IsolationNo electrical connection to patient (inherently isolated)
8.4 ENVIRONMENTAL
8.4.1 Operating Temperature
Instrument0 to 40°C
SensorWithin physiologic range for specified accuracy
8.4.2 Storage Temperature
–20 to 50°C
8.4.3 Humidity
Any humidity/temperature combination without condensation
8.4.4 Altitude
0–6200 m (0–20,000 ft)
1 Not all brands of off-the-shelf alkaline batteries provide the same battery life.
Section 7: Specifications
8-3
8.5 PHYSICAL
8.5.1 Weight (with batteries installed)
0.6 kg (1.3 lb)
8.5.2 Size
19.0 cm high × 7.6 cm wide × 6.35 cm deep(7.5 in. × 3.0 in. × 2.5 in.)
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9-1
SECTION 9: TECHNICAL SUPPLEMENT
9-1 Introduction
9-2 Functional Overview
9-3 Definition of Terms
9-4 Overall Block Diagram
9-5 SpO2 Analog Circuitry
9-6 Digital Circuitry
9-7 Circuitry Illustrations
9.1 INTRODUCTION
This Technical Supplement provides the reader with a discussion of the N-20PAcircuits. This discussion is supported with applicable illustrations, includinggraphics that have been placed on reverse-fold pages so they can be easilyreferenced while reading the text. The foldout graphics and schematics arelocated at the end of this supplement.
9.2 FUNCTIONAL OVERVIEW
The N-20PA consists of three main components:
• The N-20PA main printed circuit board (PCB)
• The N-20PA auxiliary PCB
• The N-20PA flex circuit
The relationship between these components and their interconnection isillustrated in the overall block diagram (Figure 9-1). The main componentcircuitry has been divided into the following subsections:
SpO2 analogMicroprocessorMemoryDisplay controlSensors: temperature ambient light battery voltage
PROM Measurebutton
Auxiliary PCB
Power supplyPrinter interfaceDisplay controlAudio beeper
Real- timeclock
Checkbatterybutton
Batteries
6 VDC
Patientsensor
Main PCB
20-Pin headers
Displaybacklight
Printerflex circuit Printer
Flexconnectors
Figure 9-1: Overall Block Diagram
Technical Supplement
9-2
• SpO2 Analog Block Diagram (Figure 9-2) — Analog circuitry has highsignal sensitivity and reduced susceptibility to noise. Its design allows for awide range of input signal levels and a broad range of pulsatile modulation.The SpO2 analog circuit consists of four subsections:
1. Sensor output/LED control, where the CPU controls the gain of both LEDsso that signals received at the input amplifier are in its acceptable dynamicrange
2. Input signal conditioning, where sensor output current is converted tovoltage
3. Signal gain, where the separated LED signals are amplified so their currentlevels are within the A/D converter’s acceptable range
Zeroing
and
Current toVoltage
Conversion
Inve
rter DMUX
Variable Gainand Filter
Variable Gainand Filter
OffsetSubtraction
OffsetSubtraction
Variable Gainand Filter
CPU
LED Drive
Sensor
Input SignalConditioning Signal Gain AC Ranging
SAMPIR
SAMPRED
PWM1
AC + DC
/ZERO
PWM0
REDAC
PWM2
PWM0
IRAC
AC + DC
/ZERO
IR/RED
OFF/ON
LED DIS
PWM0, PMW1, PWM2
Output
IR
RED
RSENS
IR
RED
Variable Gainand Filter
Figure 9-2: SpO2 Analog Block Diagram
4. AC ranging, where DC offset is eliminated from each LED signal
• Hardware Block Diagram (Figure 9-3) — This diagram shows the N-20PAhardware and circuits, which include: the CPU and system memory, thepower supply and power control circuitry, user controls, display and ambientlight sensors, audio output, thermal printer and ambient temperature sensor,and the real-time clock.
• Power Supply Block Diagram (Figure 9-4) — Power supply circuitry islocated on the auxiliary PCB and consists of four subsections:
1. Four “C” size batteries that provide 4-6 VDC
2. Power control circuitry that senses a press of the On/Off button and switchespower on
3. Power shutoff circuit that controls power to all circuits except the powercontrol circuit
4. Power supply circuits include: a regulated power supply at 5 VDC,unregulated power supplies of -5 VDC, 10 VDC, and 12 VDC, and ahigh-voltage power supply of 70 VDC
Technical Supplement
9-3
AnalogReferenceVoltage
AmbientLight
BatteryVoltage
AmbientTemperature
BatteryPower
PowerControl
SerialInterface
SpO2AnalogSection
PatientSensor
AddressDecoding
AddressDemultiplexing
StandardUser
Supply
PowerSupply
CPUMemory
InputPort
OutputPort
BatteryType
LithiumBattery
Real TimeClock and
Non-VolatileMemory
AudioOutput
DisplayControl
PrinterInterface
UserDisplay Optional Printer
Flex Circuit withUser Controls
CPU
Analog
Control
Analog
PowerOff
PowerControl
Pow
er O
n
Add
ress
AD BusControl
AD Bus
Enables
Digital I/O
Digital I/O
Input Port
Output Port
UserControls
Pow
er C
ontr
ol
External to Board
BUSSES
SIGNALS
Figure 9-3: N-20PA Hardware Block Diagram
Technical Supplement
9-4
Powershutoffcircuits(fuse;
EMI protect;ESD protect)AUX PCB
AUX PCB
Disposablebatteries
Powercontrolcircuits
On/Offbutton
4–6 VDCDisplay drivers
Microprocessor
Display backlight
+5 VDC
+70 VDCPowersupplycircuits AUX PCB
Main PCB
SpO2 Analogsection
(main board)
–5 VDC +10VDC
+12 VDC
Figure 9-4: Power Supply Block Diagram
• Display Control Block Diagram (Figure 9-5) — The N-20PA display iscontrolled by the display control circuitry. A sensor is used to measureambient light. During low-light conditions, the display backlight, anelectroluminescent device, is automatically switched on.
Main PCB
Microprocessor
Main PCB
Controlconditioning
circuit(generates
timingsignals)
AUX PCB
Display driver(1)
Display driver(2)
70 volts
AUX PCB
High voltagecontrol circuit
(enables+70 VDCto display)
Display
Displaybacklight
Figure 9-5: Display Control Block Diagram
• Printer Control Block Diagram (Figure 9-6) —Printer circuitry is dividedinto two subsections: the printer interface and the printer flex circuit.
Technical Supplement
9-5
Printerinterface
Printer flex
circuitPCB
Printer
Main PCB
User push buttons
AUX PCB
Microprocessor
On ADV D/D
Figure 9-6: Printer Control Block Diagram
9.3 DEFINITION OF TERMS
Analog to Digital (A/D) converter. The CPU has a 10-bit A/D converter onboard. Up to eight different analog inputs can be provided to the A/D converterfor measurement.
Central Processing Unit (CPU). An Intel 80C196KC 16-bit microcontroller.The CPU sends and receives control signals to the SpO2 analog section, display,and optional printer.
Content Addressable Memory (CAM). The CPU controls the HSO lines withthe CAM. CAM is controlled by software and programmed with eventsscheduled relative to one of two internal timers.
High Speed Outputs (HSO). The 6 HSO lines control most of the timing of theLED signal pulse and the demodulation of the received signal.
Input and Output (I/O). Digital lines that are used by the CPU to read in dataand output data.
Light Emitting Diodes (LEDs). Two LEDs are used in Nellcor oximetrysensors. Light is transmitted through body tissue and received by aphotodetector circuit that converts it to photocurrent. The two wavelengths,which are used for calculation of pulse rate and oxygen saturation in blood, aretransmitted at the following frequencies:
• infrared (IR) light at approximately 915 microns
• red light at approximately 660 microns
Pulse Width Modulation (PWM). The three 8-bit PWM outputs can besoftware controlled; their duty cycle can be changed from 0-255/256 of the totalpulse duration. PWM frequency is the crystal frequency of the CPU, which is 10MHz divided by 1024. The PWMs control the gains within the analog circuit.
RCal. Sensor RCal value is a resistance value specific to an individual sensor.This value is used by the software during oxygen saturation computations tomaximize accuracy.
Real-Time Clock (RTC). The RTC is used with the optional printer to tracktime and date for printouts.
Technical Supplement
9-6
9.4 OVERALL BLOCK DIAGRAM
Exclusive of covers, buttons, and external connectors, the N-20PA consists ofthree main components: the main PCB, the auxiliary PCB, and the displayassembly and analog shield.
• Main PCB — Contains the SpO2 analog circuitry; the CPU; supportmemory circuits; sensor circuits for ambient light, temperature, and batteryvoltage; the check battery circuit; a serial data port; and some display controlcircuits.
• Auxiliary PCB — Contains the power supply circuitry; the display drivercircuits; the real-time clock; the interface circuitry for the printer flex circuitboard (which is not used unless a printer is present); and audio outputhardware.
• Display and Analog Shield Assembly — This assembly connects to themain PCB by flex circuits. A metal shield shrouds the SpO2 analog circuitson the main PCB to protect them from EMI. An integratedelectroluminescent backlight illuminates the display under low lightconditions.
The N-20PA has an additional printer control board (printer flex circuit), andprinter hardware. Figure 9-1 shows the relationship of these components.
9.5 SPO2 ANALOG CIRCUITRY
This subsection describes the SpO2 analog hardware. The analog circuitry hashigh signal sensitivity and reduced susceptibility to noise. Its design allows for awide range of input signal levels and a broad range of pulsatile modulation. TheSpO2 analog block diagram (Figure 9-2) consists of four subsections:
• Sensor output/LED control — The CPU controls the drive level of bothLEDs so that signals received at the input amplifier are within an acceptabledynamic range. Signal channel gain may also need to be increased. TheCPU uses PWM lines to control the LED current level or to amplify thesignal channel.
• Input conditioning — Sensor detector current is converted to voltage. Ademodulation circuit minimizes the effects of other light sources and strayfrequency inputs. Because the infrared (IR) and red signals are at differentcurrent levels, the two LED signals are demultiplexed and separatelyamplified, so they can be compared with each other. Two circuits handle thedemultiplexing by alternately selecting LED signals using switches. Filtersthen remove noise and smooth the signals before sending them to theamplifiers.
• Signal gain —The separated LED signals are amplified so that their currentlevels are within the A/D converter’s acceptable range. The signals arefiltered to improve the signal-to-noise ratio, and clamped to a referencevoltage.
• AC ranging —DC offset is eliminated from each LED signal. An analogswitch sets the mean signal value to the mean of the A/D converter range,and the AC modulation is superimposed on that DC level. Then, each ACsignal is amplified and filtered to eliminate residual effects of the PWMmodulations. Finally, these two signals are input to the CPU A/D converter.
Technical Supplement
9-7
The relationship of these subsections is shown in Figure 9-7.
Patientsensor
LEDs
Input signalconditioningphotocurrent
to voltageconversion
demutiplexedto 2 channels
Main PCB
Signal gain
variable gain,filtered foreach LEDchannel
Main PCB
AC Ranging
offsetsubstraction;
additional gainand filtering
Main PCB
Microprocessor
Main PCB
To digital section
Control
Main PCB
LED drivers(red & IR)
Figure 9-7: SpO2 Analog Circuitry Block Diagram
9.5.1 Sensor Output/LED Control
The SpO2 analog circuitry provides control of the red and IR LEDs such that thereceived signals are within the dynamic range of the input amplifier. Becauseexcessive current to the LEDs will induce changes in their spectral output, it issometimes necessary to increase the received signal channel gain. To that point,the CPU controls both the current to the LEDs, and the amplification in thesignal channel.
At initialization of transmission, intensity level of the LEDs is based on previousrunning conditions; and, the transmission intensity is adjusted until the receivedsignals match the range of the A/D converter. If the LEDs reach maximumoutput without the necessary signal strength, the PWMs will increase the channelgain. The PWM lines will select either a change in the LED current or signalgain, but will not do both simultaneously.
The LED circuit switches between red and IR transmission and disables both fora time between transmissions in order to provide a no-transmission reference.To prevent excessive heat buildup and prolong battery life, each LED is on foronly a small portion of the duty cycle. Also, the frequency of switching is wellabove that of motion artifact and not a harmonic of known AC transmissions.The LED switching frequency is 1.485 kHz. The IR transmission alone, and thered transmission alone will each be on for about one-fifth of the duty cycle; thiscycle is controlled by the HSOs of the CPU.
9.5.1.1 LED Drive Circuit
The LED drive circuit is illustrated in Figure 9-8, at the end of section 9.
Technical Supplement
9-8
The IR and red LEDs are separately controlled with their drives currentsmultiplexed over two shared wires. Current to the IR LED is in the range of4.3-50.0 mA; and, current to the red LED is in the range of 6.5-75.0 mA.Currents are limited to less than 100 mA for two reasons: (1) slight excesscurrent can potentially change the emission characteristics of the LEDs, and (2)large excess current could create excessive heat at the sensor site.
The IR/red LED transmission signal (HSO1 of the CPU) is fed into the selectinputs of the triple single-pole-double-throw (SPDT) analog multiplexing switchU10, causing either the IR or the red LED transmission to be enabled.
PWM1, which is filtered by the network of R44, C37, R52, and C38, is input tothe LED drive circuit switch U10, and controls the magnitude of the IR LEDcurrent supply.
PWM2, which is filtered by the network of R43, C36, R53, and C39, is alsoinput to U10, and controls the red LED current magnitude.
Two NPN transistors (Q1 and Q2) act as current regulators for the IR and redLED return lines. Two PNP transistors (Q3 and Q4) act as switches between theIR and red LED output lines. Transistor Q5 acts as an LED drive current limiter;it clamps output of the current regulator circuit to the required level. If anyresistor in the LED drive circuit fails, current to the LED will still be limited to asafe level.
The RSENS line senses the RCal value and enables the CPU to make the propercalculations based on the type of sensor being used.
9.5.2 Input Conditioning
Input to the SpO2 analog circuit is the current output of the sensor photodiode.In order to condition the signal current, it is necessary to convert the current tovoltage.
A synchronous demodulation circuit is used to reduce the effects of other lightsources and stray frequency inputs to the system. Because the IR and red signalsare absorbed differently by body tissue, their received signal intensities are atdifferent levels. Therefore, the IR and red signals must be demodulated and thenamplified separately in order to compare them to each other. Demultiplexing isaccomplished by means of two circuits that alternately select the IR and redsignals. Selection of the circuits is controlled by two switches that arecoordinated with the IR and red transmissions. A filter with a large timeconstant follows to smooth the signal and remove noise before amplification.
9.5.1.2 Differential Synchronous Demodulation Circuit
The differential synchronous demodulation circuit is illustrated in Figure 9-9.
Before the current from the photodetector is converted to voltage, C40 and R17filter any high frequency noise. The op-amp U1A is used in parallel with thecurrent-to-voltage converter U1D to cancel any DC voltage, effectively ACcoupling the output of U1D. The average value of the SpO2 analog referencevoltage (VREF) of U1D, 5 V, is measured at test point 49.
Technical Supplement
9-9
15.8K
R56
LT1013
U9B
5 4
3PHOTOI
VREF
40.2KR57
L1
TP44SENSORINPUT
DB9F
P1
1 6 2 7 3 8 4 9 5
LF444
U1A
11
4
1 2
3182K
R1
390PFC40
3.32KR58
3.32KR17
1M
R2
VREF
LF444
U1D
14 13
12
TP49
.047UFC22
.047UFC59
511KR157
280KR19
VREF
18PF
C1
-5V
LTC201U6B
14 15
61
LTC201U6A
3 2
1
+12V
.1%88.7K
R159
LT1097
U35
4 81
57
6 3
2
-5V
+12V
LTC201U6D
7 6
8
.1%88.7KR158
2.0KR63
51.1K
R160
1M
R23
VREF
TP79
TP78
LTC201U6C 10
9 11
VREF
3.32K
R27
3.32K
R26
.47UFC25
.47UFC24
82.5K
VREF
SAMPREDSAMPIROFF/ON
RED
IR
Figure 9-9: Differential Synchronous Demodulation Circuit
The same line that controls the on/off pulsing of the LEDs controls U6D, asingle-pole-single-throw (SPST) analog switch. When either of the LEDs is on(the line is low and the switch is closed), U35 is used as a noninvertingamplifier. When the LEDs are both off, U35 is used as an inverting amplifier.The signal at the output of amplifier U35 is then demultiplexed.
The CPU HSO lines SAMPRED and SAMPIR, which are both active low,control SPST analog switches U6A and U6B respectively. Switch U6A is closedto sample the red signal; switch U6B is closed to sample the IR signal. Thesampling rate for both switches is 10 kHz. Switching is coordinated with theLED transmission so that the IR and red signals are each sampled twice percycle; that is, once when the LED is off (signal inverted), and once when theLED is on (signal not inverted). The filtering circuit that follows has a long timeconstant, thereby acting as an averaging circuit.
A simplified N-20PA HSO timing diagram is illustrated in Figure 9-10, at theend of Section 9.
Technical Supplement
9-10
If the instantaneous average photocurrent (DC offset) is excessive and U1Dcannot bring it to VREF, the PHOTOI line to the CPU (HSI0) is activated. Thisaction is an indication of excess ambient light into the photosensor, or theoccurrence of excess noise in the input circuit. It also serves as a warning to theinstrument that the sensor signal may be contaminated and causes the software tosend an error message. After about 3 seconds of continuous photocurrent signal,pulse search annunciation will begin. After about 10 seconds of continuousphotocurrent signal, zeros will be displayed.
9.5.3 Signal Gain
The separated IR and red signals are amplified so that their DC values are withinthe range of the A/D converter. Because the received IR and red signals aretypically at different current levels, the signal gain circuits provide independentamplification for each signal as needed. The gain in these circuits is adjusted bymeans of the PWM lines.
After the IR and red signals are amplified, they are filtered to improve thesignal-to-noise ratio and clamped to a reference voltage to prevent the combinedAC and DC signals from exceeding an acceptable input voltage from the A/Dconverter.
9.5.3.1 Variable Gain Circuit
The variable gain circuits are illustrated in Figure 9-11.
3.32K
R26
.47UFC24
1NF
C33
1NFC34
82.5K
R25
82.5K
R24
VREF 2N3906
Q7 220PF
C127
220PFC126
2N3906
Q6
TP52
TP51LF444
U1C8
10
9
LF444
U1B
75
6
VREF
VREF
-5V
.1UF
C35
.1UF
C122VREF
47.5K
R39
OFF/ON
4053
U2
7VEE
8VSS
16VDD
4Z
15Y
14X
9C
10B
11A
6INH
3Z1
5Z0
1Y1
2Y0
13X1
12X0
VCC PWM1IR LED/AV
To LED controlPWM2
RED
IR
IR
RED
Figure 9-11: Variable Gain Circuit
Technical Supplement
9-11
The two variable gain circuits are functionally equivalent. The gain of eachcircuit is contingent upon the signals received level and is controlled to bringeach signal to approximately 3.5 V. Each circuit uses an amplifier and oneswitch in the triple SPDT analog multiplexing unit U2.
The gain in each of the circuits is accomplished by means of a feedback loop,which includes one of the SPDT switches in U2. The PWMs control whether thefeedback loop is connected to ground or to the amplifier output. The feedback isthen averaged by C33/R25 (red), and C34/R24 (IR). The higher the value ofPWM2, the greater the IR gain; the higher the value of PWM1, the greater thered gain.
9.5.3.2 Filtering Circuit
The filtering circuits are illustrated in Figure 9-12.
1N914
CR4
1N914
CR2
VREF
.068UF
C20
OP490SO
U4B
76
5
-5V
1N914CR3
100K
R13
100K
R12
R11
R10
100K
R9
100K
R8
100K
R7
100K
R6
.068UFC17
.068UF
C14
.068UFC15
.12UFC19
C18
.12UF
C16
OP490SO
U4D
1615
14
U4A
31
4
1
+12V
1N914
CR1
U4C
10 11
12
VREF
.12UF
C13
TP90
TP82
TP89
TP81
100K
100K.12UF
OP490SO
2
3
OP490SO
IRDC
REDDC
RED
IR
Figure 9-12: Filtering Circuit
These circuits consist of two cascaded second-order filters with a breakfrequency of 10 Hz. Pairs of diodes (D1/D3 and D2/D4) that are locatedbetween VREF and ground at the positive inputs of the second amplifiers,maintain the voltage output within the range of the A/D converter.
Technical Supplement
9-12
9.5.4 AC Ranging
In order to achieve a specified level of oxygen saturation measurement and tostill use a standard-type combined CPU and A/D converter, the DC offset issubtracted from each signal. Because the DC portion of the signal can be on theorder of one thousand times the AC modulation, 16 bits of A/D conversionwould otherwise be required to accurately compare the IR and red modulationsbetween the combined AC and DC signals. The DC offsets are subtracted byusing an analog switch to set the mean signal value to the mean of the range ofthe A/D converter whenever necessary. The AC modulation is thensuperimposed upon that DC level. This is known as AC ranging.
Each AC signal is subsequently amplified such that its peak-to-peak values spanone-fifth of the range of the A/D converter. The amplified AC signals are thenfiltered to remove the residual effects of the PWM modulations and finally, areinput to the CPU. The combined AC and DC signals for both IR and red signalsare separately input to the A/D converter.
9.5.4.1 Offset Subtraction Circuits
The AC variable gain control circuit is illustrated in Figure 9-13, at the end ofthis section.
Voltage dividers R22 and R41 (red), and R31 and R5 (IR), which are locatedbetween VREF and ground, establish a baseline voltage of 2.75 V at the input ofthe unity gain amplifiers U7C (red) and U7D (IR).
Whenever SPST analog switches U11A and U11D are closed by HSO0 (activelow), the DC portions of the IR and red signals create a charge, which is storedon C29 and C89, respectively. These capacitors hold this charge even after theswitches are opened and the resulting voltage is subtracted from the combinedsignal—leaving only the AC modulation output. This AC signal issuperimposed on the baseline voltage output by U7C and U7D. The IRDC andREDDC are then filtered and input to the CPU, and can be measured at TP58and TP54, respectively.
9.5.4.1 AC Variable Gain Control Circuits
The AC variable gain control circuit is illustrated in Figure 9-13, at the end ofsection 9.
The AC modulations are amplified by U7A (red) and U7B (IR) andsuperimposed on the baseline voltages present at the output of U7D (IR) andU7C (red). The amplification is handled by means of the SPDT analogmultiplexing switch U3 within the feedback loop, which increases gain asPWM0 is increased. The IRAC and REDAC are then filtered and input to theCPU, and can be measured at TP55 and TP59, respectively.
9.6 DIGITAL CIRCUITRY
The digital hardware and related circuitry, which is illustrated in Figure 9-14,includes the following subsystems:
• CPU — A 16-bit microcontroller that includes: a serial port, watchdogtimer, A/D converter with an 8-input analog multiplexer, 3-pulse widthmodulators, and a high speed I/O subsystem.
Technical Supplement
9-13
• System memory — System memory is external to the CPU and consists ofan 8K × 8 static RAM and a 64K × 16 EPROM.
• Real-Time Clock (RTC) — The RTC keeps track of date and time, which isprinted on each printout. A lithium battery designed to last up to 5 yearsbefore needing replacement powers the RTC.
• Audio output — A piezoelectric ceramic beeper is used for audio output.
• Display control — A high-visibility display provides oxygen saturation andpulse rate values. An ambient light sensor responds to low-light conditionsand turns on the display backlight.
• User controls — A On/Off button and a battery-check button. The On/Offbutton signals the power control circuit to switch on the power supply. Pressand hold the battery-check button to display a percentage of useful liferemaining in the batteries.
• Power supply/Power control circuitry — The N-20PA receives powerfrom 4 “C” cell batteries. The power control circuitry discontinues power tothe unit when the batteries are no longer reliable.
• Thermal printer — Generates a hard copy of oxygen saturation and pulserate values. A sensor monitors ambient temperature and adjusts printeroutput to ensure consistent print quality.
MeasureCheck Battery
Power supply& control
N-20/N-20P Control buttons
AUXPCB Ambient
light sensorMainPCB
CPU
Main PCB
Memory&
software
To analog section
Real-timeclock
AUXPCB
Ambienttemp. sensor
MainPCB
ON ADV D/D
Printer
Audio beeper
(N-20 only)
Displaydrivers
Printer Control button
AUX PCB
Display
AUX PCB
Figure 9-14: Digital Circuitry Block Diagram
9.6.1 CPU
The CPU circuit is illustrated in Figure 9-15, at the end of this section.
The Intel 80C196KC CPU is a 16-bit microcontroller with built-in peripheralsincluding a serial port, watchdog timer, A/D converter with an 8-input analogmultiplexer, three pulse width modulators, two 16-bit counter/timers, up to 48I/O lines, and a high speed I/O subsystem.
Technical Supplement
9-14
The CPU is capable of running up to 16 MHz; however, it is run at 10 MHz fordecreased power consumption. All unused inputs are tied to either Vcc orground through resistors—this prevents unused inputs floating to any voltageand causing excess power drain. The READY input pin is tied high, therebydisabling wait-state generation; all bus accesses are zero-wait state. The EA pinis tied low to enable addressing of the external EPROM.
When the power supply is first switched on by the power control circuit, thereset generation circuit holds the CPU RESET pin low for at least 20 ms, thenallows the internal pull-up resistor to bring it high; this assures a good CPUreset.
An internal watchdog timer is enabled and runs continuously. The watchdogtimer provides a means of recovering from a software glitch caused by ESD,EMI, and so forth. If the software does not clear the timer at least every 64Kstate-times (13.1 ms), the CPU will drive RESET low, resetting the entire unit.The reset output by the CPU is only 16 state-times long (3.2 µs). Q22 providesisolation from C65 so the CPU can drive a good reset to the display controlcircuit.
The CPU has the ability to dynamically switch the data bus width—based on theBUSWIDTH input pin. A low on BUSWIDTH tells the CPU to access memoryonly 8 bits at a time. When accessing the static RAM, BUSWIDTH is low,automatically reading the 8-bit wide RAM. Since BUSWIDTH is connected tothe active low RAM enable line (RAMEN), all other memory and mapped I/Oare read or written 16 bits at a time.
The CPU measures eight analog inputs. Input from the SpO2 analog sectionincludes AC and DC signals for the oximeter sensor red and infrared channels,and the sensor calibration resistor RSENS. Light, temperature, and batteryvoltage are also measured.
The N-20PA CPU is configured as follows:
• Decoded AD0 and BHE generate separate WR write strobes for the low andhigh bytes of a word. The signal WR (pin WRL) is the low-byte writestrobe.
• A standard address latch enable (ALE) is generated and used.
• HSO pins 4 and 5 are configured as outputs. The HSO is used to generatestable timing control signals to the SpO2 analog section, display, and printer.
• The timer-2 external control pins: T2CLK, T2RST, T2U-D, and T2CAPT—are disabled via software and used as standard I/O.
• The HOLD, HLDA, and BREQ bus accessing is disabled via software andthe pins are used as standard I/O.
• Pins HSI0 and EXTINT are configured for interrupt input. The CPUreceives 2 external interrupts (signals PR_TACH and PHOTOI).
• RXD and TXD are configured as a standard asynchronous serial transmitterand receiver for the serial interface.
• PWM0, PWM1, and PWM2 pins are configured as pulse width modulatoroutputs. They are used to control gains within the SpO2 analog section.
9.6.1.1 Address Demultiplexing
The address demultiplexing circuit is illustrated in Figure 9-16.
Technical Supplement
9-15
10KR109
TP40
TP39
AD15AD14AD13AD12AD11AD10AD9AD8
ALE
ALE
AD7AD6AD5AD4
74HC573
U33
1OC
11C
12Q8
9D8
13Q7
8D7
14Q6
7D6
15Q5
6D5
16Q4
5D4
17Q3
4D3
18Q2
3D2
19Q1
2D1
10KR108
A15A14A13A12A11A10A9A8
A7A6A5A4
74HC573
U13
1OC
11C
12Q8
9D8
13Q7
8D7
14Q6
7D6
15Q5
6D5
16Q4
5D4
17Q3
4D3
18Q2
3D2
19Q1
2D1
A3A2A1A0
ADDRESS DEMUX
AD3AD2AD1AD0
Figure 9-16: Address Demultiplexing Circuit
U13 and U33 are transparent latches that latch the address portion of the AD busdata on the falling edge of ALE; the outputs are always enabled. The outputs ofU13 and U33 are always the address portion of the AD bus.
9.6.1.2 Address Decoding
The address decoding circuit is illustrated in Figure 9-17.
The CPU has a 64 Kbyte address range of 0-FFFF. RAM, EPROM, and I/Oports share this space. The address decoding circuit splits up this space andoutput enable lines to the RAM, EPROM, and I/O ports.
U30A generates the static RAMs active low enable signal, RAMEN. Whenaddress lines A13, A14, A15 are all high, U30A’s output goes low, enabling theRAM. This occurs for the 8K address range of E000-FFFF.
Technical Supplement
9-16
A10
A11
TP71
A15ROMEN
10K
R134
0000-DBFF
VCC
74HC10
U30C
8 11 10 9
74HC10
U30A
12 13 2 1
TP74
RAMEN
TO: N-20
AUX PCB
DC00-DFFF
E000-FFFF
74HC10
U30B
6 5 4 3
74HC138
U28
7Y7
9Y6
10Y5
11Y4
12Y3
13Y2
14Y1
15Y0
5G2B
4G2A
6G1
3C
2B
1A
A14
ADDRESS DECODING
WR
A14A15
A13
RD
A12
EXOUTEN
EXINEN
20 HDR
20
19
Figure 9-17: Address Decoding Circuit
U30B and U28 are used to generate the input port and output port active lowenable signals EXINEN and EXOUTEN. When address lines A15, A14, A11,and A10 are high, and A13 is low, U28 becomes enabled. With U28 enabled,one of the 8 outputs is set low. The output to go low is selected by pins A, B,and C. They form a 3-bit binary number with pin C being the most significantbit. So when address line A12 is high, WR active (low) and RD inactive (high),a binary 5 is produced on pins A, B, and C, forcing output Y5 (EXOUTEN) low.This enables the output port for writing. When address line A12 is high, WRinactive and RD active, a binary 3 is produced on pins A, B, and C, forcingoutput Y3 (EXINEN) low. Note that in both previous conditions, A15, A14,A12, A11, and A10 are high and A13 is low.
The input port and the output port both share the same 1 Kbyte address space ofDC00-DFFF. When data are written to that address, the output port enablesignal EXOUTEN is activated. But when data are read from the same address,EXINEN is activated. Because the CPU is configured to use a 16-bit bus, exceptfor RAM, any even address in the DC00-DFF range could be used for externalport access. In other words, reading or writing address DC00, DC02, DC04, andso on, will all produce the same results. Due to the CPU configuration, the writestrobe WR (WRL pin), is only active for low-byte writes; therefore, both bytesof the external output port must be written to at the same time. Because, theupper byte of the output port cannot be written to alone, no write strobe and,therefore, no EXOUTEN signal will be generated.
Technical Supplement
9-17
U30C generates the EPROMs active low enable signal, ROMEN. The activelow signals RAMEN and EXINEN are basically used as EPROM disable signals.When RAMEN or EXINEN or test point TP71 are low, the output of U30C,ROMEN, is forced high, disabling the ROM. Therefore, the EPROM is disabledfor the range DC00-FFFF and enabled for the 55 Kbyte address range of0h-DBFF. TP71 is used during board testing to disable the EPROM.
9.6.2 CPU Memory
The CPU memory circuit is illustrated in Figure 9-18.
AD7AD6AD5AD4AD3AD2AD1
AD15AD14AD13AD12AD11AD10
AD9AD8
ROMEN
VCCVCC
RD
A15A14A13A12A11A10A9A8A7A6A5A4A3A2
TP43
27C1024L
U15
4O15
5O14
6O13
7O12
8O11
9O10
10O9
11O8
14O7
15O6
16O5
17O4
18O3
19O2
20O1
21O0
43PGM
2VPP
22OE
3
41A15
40A14
39A13
38A12
37A11
36A10
35A9
32A8
31A7
30A6
29A5
28A4
27A3
26A2
25A1
24A0
RAMEN
WR
64K X 16 EPROM
A1
A12A11A10A9A8
RD
A7A6A5A4
10KR133
VCC
AD0
AD7AD6AD5AD4AD3AD2AD1AD0
U14
19D7
18D6
17D5
16D4
15D3
13D2
12D1
11D0
22OE
27WE
26CS2
20CS1
2A12
23A11
21A10
24A9
25A8
3A7
4A6
5A5
6A4
7A3
8A2
9A1
10A0
8K X 8 SRAM
A3A2A1A0
CE
Figure 9-18: CPU Memory Circuit
The memory system external to the CPU consists of an 8 K × 8 static RAM(U14) and a 64 K × 16 EPROM (U15). The EPROM is 16 bits wide to enhanceCPU performance. Because RAM is infrequently accessed, it is only 8 bits wide.
U14 is a standard 8K × 8 static RAM. Test point TP 43 is used during testing todisable the output.
Technical Supplement
9-18
The program that the CPU runs is stored in U15. U15 is a 16-bit wide output,one-time programmable (OTP) EPROM. During 16-bit wide bus accesses, theCPU uses address line A0 for low/high byte selection. A0 is not used as anormal address line. The CPU can only address 64K × 8 bytes or 32K × 16bytes. Pin A15 of U15 is tied low, always selecting the lower half of theEPROM. Signal ROMEN is then used to enable the EPROM for the propermemory area.
9.6.2.1 Input Port
The input port circuit is illustrated in Figure 9-19.
EXINEN 74HC573
U16
1OC
11C
12Q8
9D8
13Q7
8D7
14Q6
7D6
15Q5
6D5
16Q4
5D4
17Q3
4D3
18Q2
3D2
19Q1
2D1
EX_IN INPUT PORT
RTC_IOBAT_TYPEPR_HOMEADV_BTNDD_BTNON_OFF_BTN
GO_BTN
VCC
AD7AD6AD5AD4AD3AD2AD1AD0
Figure 9-19: Input Port Circuit
U16 is the input port external to the CPU. The logic levels on the inputs (pinsD1-D8) are output to the CPU via the AD bus while EXINEN is strobed low. Allof the user control buttons are input via U16. Also, the battery type is senses viaU16; a high on signal BAT_TYPE signifies to the CPU that rechargeablebatteries are being used. If the optional printer head is in the home position,PR_HOME will be a logic high.
Pin D8 (RTC_IO) and an output bit of the external output port are connected.They work as a pair to create a bidirectional bit for communicating with the RTC(see Section 6.3, Real-Time Clock and Non-Volatile Memory).
9.6.2.2 Output Port
The output port circuit is illustrated in Figure 9-20, at the end of Section 9.
The output port external to the CPU consists of 2 octal D latches, U18 and U17;they function as a single 16-bit output port. U18 is the lower byte (LSB) andU17 is the upper byte (MSB). The output of U18 is always enabled. The outputbits of U18 control audio output, optional printer, RTC, and display.
Technical Supplement
9-19
The signal PR_STROBE controls U17’s output drivers. Under normal operation,the outputs are tristated and resistors R148-R154 pull the outputs low.PR_STROBE is driven low to turn on the output drivers of U17. SignalsPR_DOT0-PR_DOT6 (pins Q1-Q7) drive the 7 print dots of the optional printer.PR_STROBE pulses all 7 of the dot lines for a specific time period (see alsoPrinter Interface, Section 6.14). When the CPU is first powered on,PR_STROBE is in a tristate condition. R123 assures that U17 does notaccidentally turn on the printer head dots until required to. Pin Q8 (RTC_IO)and an input bit of the external input port are connected. They work as a pair tocreate a bidirectional bit for communicating with the RTC (see also “Real-TimeClock and Nonvolatile Memory”).
Both bytes of external output port (that is, U18 and U17) must be written to atthe same time. The upper byte of the output port (U17) cannot be written toindependently (see also “Address Decoding”).
9.6.3 Real-Time Clock (RTC) and Nonvolatile Memory
The Real-Time Clock Circuit is illustrated in Figure 9-21.
3.32K
R163
1N914
CR23
1N914CR22
DS1202S
U29
8 5 3
16
9RST
12I/O
14SCLK
TEST
TP76
.1uF
C114
32.768KHz
Y1
3VBT1
TEST
TP86
TEST
TP87
TEST
TP85
RTC_RST
RTC_IORTC_CLK
REAL TIME CLOCKVCC
GND
X1VCC
X2
Figure 9-21: Real-Time Clock Circuit
The RTC has two functions: (1) it provides nonvolatile memory that is used toremember whether the printer should be enabled at power-on, and (2) to keeptrack of time and date for the N-20PA printer. The N-20PA does not require oruse the RTC; it is disabled via software.
The RTC chip U29 uses a 3-wire synchronous serial interface to communicatewith the CPU. The CPU brings signal RTC_RST high to activatecommunication with the RTC. RTC_CLK clocks data into and out of the RTCchip. RTC_IO is the bidirectional communication data bit. The CPU drivesRTC_IO when writing data and commands to the RTC. The CPU tristatesRTC_IO and then reads data back onto it from the RTC.
Technical Supplement
9-20
Crystal Y1 provides an accurate 32.768 KHz clock input whenever thetimekeeping circuitry of U29 is activated. The CPU only enables thetimekeeping function when an optional printer is installed. If no printer isinstalled, the CPU switches off timekeeping, thereby extending battery life.Also, with no printer installed, the RTC clock is only used during diagnostictesting to verify the CPU clock timing.
The lithium battery BT1 and diodes CR22 and CR23 provide the power switchover and constant power needed to keep the time and RAM data while the unit isnot in use. Whenever the unit is powered on, Vcc is at 5 V and U29 is poweredvia CR22. CR 23 is reverse biased because BT1 at 3 V is at a lower potentialthan Vcc. Whenever the unit is powered off, the potential between Vcc andswitched ground is 0 V, CR23 is forward biased, and U29 is powered by BT1.CR22 is reverse biased, isolating BT1 from Vcc. This circuit design allows BT1life of up to 5 years typical, without the unit being powered on.
U29 holds 24 bytes of RAM, which is used for nonvolatile storage of CPU data.
9.6.4 Audio Output
The audio output circuit is illustrated in Figure 9-22.
TESTTP75 TEST
TP74
BEEPER
BEEP_2BEEP_1
AT17
BZ1
Figure 9-22: Audio Output Circuit
BZ1, a piezo ceramic sounder, is the audio output device. Due to its low drivecurrent of 2 mA maximum, no drive circuitry is needed and is driven directlyfrom the external output port. The audio output device is differentially drivenwith 2 square waves 180 degrees out of phase. The drive frequency isapproximately 1480 Hz or 740 Hz and is generated by the CPU. BZ1 isdifferentially driven to obtain maximum audible volume.
9.6.5 Display Control Circuitry
The display control circuit is illustrated in Figure 9-23, at the end of Section 9.Figure 9-5 shows the display control block diagram.
The Taliq display is controlled by the display control circuitry. A photosensormeasures ambient light and automatically switches on the electroluminscentdisplay backlight during low-light conditions. The display control circuitry isdivided into the following subsections:
• Control Conditioning Circuit (main PCB) — The control conditioningcircuit processes signals generated by the CPU to produce timing signals forthe display drivers.
• Display Driver ICs (auxiliary PCB) — Each of the two display driver ICshave 32 high-voltage outputs that enable individual segments of the displayto be turned on or off.
Technical Supplement
9-21
• High Voltage Control Circuit (auxiliary PCB) — The high-voltage controlcircuit allows the CPU to switch on or off the display’s high-voltage input.
9.6.5.1 Control Conditioning Circuit
The CPU generates a 400 µs low-pulse train at a 160 Hz rate on signalDISP_PHASE. Half of U34 takes DISP_PHASE as an input and createsDISP_POL as an 80 Hz 50% duty cycle square wave. A CPU reset initializesDISP_POL low when any CPU reset occurs so the software knows the initialstate. The other half of U34 is used to synchronize the rising edge of theDISP_DL with the rising edge of DISP_POL. The CPU brings DISP_LATCHsignal high before the rising edge of DISP_PHASE; this allows the high to beclocked out to DISP_DL on the rising edge of DISP_PHASE. About 100 µsafter the rising edge of DISP_PHASE, the CPU brings DISP_LATCH low,asynchronously resetting DISP_DL low.
9.6.5.2 Display Driver Control Circuits
U19 and U20 are the display segment driver chips. Each chip has 32high-voltage outputs and a common display marked BP (backplane). The CPUvia a serial shift register input inputs the display data to U19 and U20. U19 andU20 are daisy-chained together forming a 64-bit serial shift register. Displaydata are loaded and shifted down via the DISP_DATA and DISP_CLK signals.When all 64 bits of the shift register are loaded, a high pulse on DISP_DLupdates the display, all 64 bits at the same time. The display is clocked with an80 Hz 50% duty cycle waveform by signal DISP_POL. DC voltages cannotdrive the display or display damage will result. Creating a 180-degree phaseshift between the segment pin and the BP common pin illuminates displaysegments. Segments are left dark by making the waveform on the segment pinbe in phase with the BP pin. The display has an electroluminescent (EL)backlight, and is driven the same as the display segments. Connectors JP2, JP3,and JP5 connect the display and EL backlight to the drive electronics.
9.6.5.3 High Voltage Control Circuit
The cold switch circuit performs two basic functions: (1) it allows the CPU toenable and disable the display high voltage VDISP, and (2) it slows the edgeslew rate of the segment drivers as it switches the high voltage. When the signalDISP_PHASE is low, Q14 is disabled, pulling VDISP low. Whenever the CPUis powered on, DISP_PHASE is tristated. The base emitter junction of Q12 pullsDISP_PHASE low, disabling the high voltage. This assures that the high voltageis only enabled to the display when controlled by the CPU.
The Taliq display is similar to an LCD in that the load of a segment is mainlycapacitive. A cold switch circuit provides a current-limited 70 V to VDISP.R93, R95, Q21, and Q14 do the on/off switching and current limiting. As thedriver chips’ output waveforms and DISP_PHASE change states, the capacitiveloads of the display cause VDISP to limit current until the capacitance is fullycharged. This constant output current is integrated into the display capacitiveloads, causing a highly linear rising and falling voltage ramp on VDISP.Because the high voltage to the drive chips (VDISP) is ramped, the outputs ofthe driver chips U19 and U20 are also ramped at the same controlled rate. Thisdesign is used to reduce current spikes on the 70 V power supply, and, inaddition, to reduce the EMI generated by the display due to the lower slew ratesof the high-voltage switching signals.
Technical Supplement
9-22
9.6.6 Standard User Controls
The user-controls circuit is illustrated in Figure 9-24.
The standard user controls consist of two momentary push-button switches(On/Off and battery-check). The Of/Off button is an elastomeric contact switch,and the battery-check button is a mechanical momentary switch.
The CPU input lines BAT_BTN and GO_BTN are normally pulled to the highstate by R71 and R78. Whenever a button is pressed, the CPU input line ispulled low through R74 and R80. The switch contacts are debounced with C64and C66. L11, L12, C126, and C123 provide a current path for ESD protection.
In addition to being read by the CPU, the On/Off button also activates the powersupply via the power control circuit. Note that the On/Off button has circuitryon both the main PCB as well as the auxiliary PCB.
Technical Supplement
9-23
S2MEASUREBUTTON
221
R80JP8
2
1
TO: N-20AUX PCB
GO_SW
TEST
TP81
TEST
TP88
100PFC126
L12
SW1 .01UFC64
1K
R74BAT_BTN
CHECK BATTERY
150KR71
VCC
JP18
2
1
L11GO_SW
TESTTP71
100PF
C123
3.32KR79
15KR102
TEST
TP72
GO_BTN
VCC
.01UFC66
VCON
150KR78
MAIN PCBTO: N-20
GO BTN
To U21pin 4
Figure 9-24: User Controls Circuit
Power Supply/Power Control Circuitry
Power supply circuitry is located on the auxiliary PCB and consists of thefollowing subsections:
• Batteries — Four 1.5-V alkaline “C” size batteries provide 4–6 VDC power.
• Power control circuitry — Power control circuitry is connected to thebatteries. It senses any press of the On/Off button and switches on the powersupplies. Reverse current limiting protects the N-20PA from damage ifbatteries are inserted incorrectly.
Technical Supplement
9-24
• Power shutoff circuit — This circuit controls power to all circuits except thepower control circuit. In addition, a fuse protects the power supply fromexcessive current draw. The power supply is also protected againstelectrostatic discharge and electromagnetic interference.
• Power supply circuits consist of the following power supplies:
Regulated power supply: Power supplied by the batteries is regulatedat 5 VDC. This supply is used by all of the digital circuitry and some ofthe SpO2 analog circuitry.
Unregulated power supplies: 5 VDC is converted by a switchedcapacitor network into unregulated power supplies of -5 VDC, 10 VDC,and 12 VDC, all of which are used in the SpO2 analog circuits.
High voltage power supply: A voltage regulator/doubler convertsbattery power to 70 VDC; this increase in power is needed by thedisplay drivers as well as the display backlight.
The power supply circuit is illustrated in Figure 9-25, at the end of Section 9.Figure 9-4 shows the power supply block diagram.
9.6.7.1 Power Control Circuitry
The power control circuit is illustrated in Figure 9-26, at the end of Section 9.
The power control circuit consists of U21 and its associated components. U21 isa D flip-flop with asynchronous preset and clear; only the preset and clear areused.
Power is applied to U21 via CR11 whenever batteries are installed. CR11provides protection for U21 if the batteries are installed with reverse polarity.This error condition will reverse bias CR11, thereby disabling current flow toU21.
The much larger RC time constant of R110, C67 compared to R78, C66guarantees that the unit will not be accidentally powered-on when batteries arefirst installed.
Whenever the measure button is pressed, a low on GO_SW sets the output signalPWR_ON high. This condition connects switched and battery grounds, enablesthe power supplies, and switches on the unit. Whenever the CPU determinesthat the power should be switched off, it forces PWR_DOWN low. This actionclears output PWR_ON to a logic low, disconnecting ground, and switching offthe power supplies (see also “Power Supply”).
R79 and R81 provide current limit protection to U21 inputs. They also limit thecurrent that will flow through U21 inputs to the CPU when the batteries areinstalled backward. In the reverse battery error condition, excessive current canflow from the inputs of U21 through the input protection diodes or substrateinside the CPUs integrated circuit or through both. These resistors limit thatcurrent path to safe levels.
Technical Supplement
9-25
9.6.7.2 Power Shutoff Circuit
This circuit is illustrated in Figure 9-25, Power Supply Circuit.
Fuse F1 protects the unit from excessive current draw. CR24 protects againstlarge voltage transients caused by ESD, EMI, and so on.
Q15 is a dual-channel FET; the drain of Q15 part 2 (pin D2) is connected tobattery ground; the gate (G2) is connected to battery plus; and R155 applies abias to the source (S2) so it will switch on when a positive voltage is applied toG2. When batteries are correctly installed, Q15 part 2 is switched on andconducts current. If batteries are installed backward, Q15 part 2 switches off anddisables current flow. This protects the unit’s power supply circuitry from anaccidental reversal of battery potential.
Q15 part 1 controls the power supplies. When a logic high is placed on the gate(pin G1) signal PWR_ON battery ground is connected to the circuit and switchedto ground via Q15 parts 1 and 2. When the power control circuitry pullsPWR_ON low, switched ground switches to a high impedance state. This actionswitches off the power supply and, therefore the unit, except for the powercontrol circuit.
9.6.7.3 Vcc Power Supply
This circuit is illustrated in Figure 9-25, Power Supply Circuit.
The Vcc power supply is a switched inductor voltage regulator operating inboost mode (U22). The power input is provided by the batteries (VBAT).NFET (Q17) operates as a linear post regulator. The 1 M resistor (R77) operatesas a static bleed device across the switched regulator when the regulator isswitched down. The regulated output is Vcc (5 V ± 5%).
9.6.7.4 Raw Power Supplies
This circuit is illustrated in Figure 9-25, Power Supply Circuit.
The input to the raw power supplies is Vcc, which is a switched-capacitorvoltage converter operating in separate multiply and invert modes in conjunctionwith supporting circuitry. U23 inverts Vcc and outputs raw –5 V. Raw 10 V isderived by voltage doubling Vcc with CR14, CR19, CR20, and CR78. Raw 12V is derived by voltage tripling Vcc with CR15, Q8, Q9, C96, C81, R119, andR120.
The raw power supplies are used as bias supplies for the SpO2 analog sectionand are not tightly regulated. The normal operating range of the raw powersupplies are:
raw –5.0 V = –6.0 V to –4.0 Vraw 10.0 V = 7.5 V to 11.0 Vraw 12.0 V = 12.0 V to 15.0 V
Technical Supplement
9-26
9.6.7.5 High Voltage Supply
This circuit is illustrated in Figure 9-25, Power Supply Circuit.
The batteries (VBAT) provide the input power for the high-voltage supply. Thehigh-voltage supply is a switched-inductor voltage regulator (U26) that operatesin conjunction with a capacitive voltage doubler to output 72 VDC ± 5%. Toprotect against a runaway voltage condition, CR25 clamps U26 output to a safelevel.
9.6.8 Analog Reference Voltage
The analog reference voltage circuit is illustrated in Figure 9-27.
U32 provides an accurate, regulated voltage that is used as the reference voltagefor the A/D converter inside the CPU. C6, C12, and R124 provide filtering. Thevoltage output VREF is 5 V.
+5.7
2N3904Q24
VREF
TP62
TP61
-5V
22UFC93
+12V
22UFC91
221
R122
221
R121
RAW-5V
0.1UFC94
RAW12V
0.1UFC80
182
R123RAW10V
22UFC95
10K
R161
2N3904Q23
TP60
GNDTP70
1
R124
22UFC12
LT1021
U32
5TRIM
6VOUT
4GND
2VIN
VREF
0.1UFC6
Figure 9-27: Analog Reference Voltage Circuit
Technical Supplement
9-27
9.6.9 Ambient Light
The ambient light circuit is illustrated in Figure 9-28.
33.2KR136
TP72
.01UFC63
2.2MR68
MMBTA13LQ8
VCC
VTB8442BD8
LIGHT SENSOR
VCC
AmbientLight
Figure 9-28: Ambient Light Circuit
Diode D8 is a photodiode that is used to measure ambient light. Q8, R68, andR136 provide current gain for D8’s photocurrent. The amplified photocurrentflowing through R136 creates a voltage drop, which is measured by the CPU.The CPU continually monitors the light source output at AMB_LIGHT (TP72).Under low-ambient light conditions, the CPU automatically switches on thedisplay backlight.
9.6.10 Ambient Temperature
The ambient temperature circuit is illustrated in Figure 9-29.
0.1uFC115
LM35
U5 1
VCC
3GND
2TEMP
TEMP SENSOR
VCC
PR_TEMP
Figure 9-29: Ambient Temperature Circuit
U5 is a precision-temperature sensor. It outputs (PR_TEMP) a voltageproportional to the ambient temperature, which is 10 mV per degree centigrade.For example, at a room temperature of 25 °C, the U5 output would be 250 mV.U5 is used to compensate for ambient temperatures associated with thermalprinters.
Technical Supplement
9-28
9.6.11 Battery Voltage
The battery voltage circuit is illustrated in Figure 9-30.
.01UFC62
1%47.5K R70
BATTERYVOLTAGESENSE
BAT_VOLT
TP73
1%15.8K R69
VBAT
Figure 9-30: Battery Voltage Circuit
The analog input voltage range of the CPU is 0-5 VDC. Because the batteryvoltage may be as high as 6.2 V, R69 and R70 form a voltage divider to decreasethe measured battery voltage to a usable level. The gain is 0.75; thus, if thebattery voltage was 6 V, then the voltage of BAT_VOLT would be 6 × 0.75which equals 4.5 V.
The software has the ability to determine when battery power is too low. If thesoftware determines that the battery voltage is too low to provide accurateinformation, the software generates an audible signal and automatically switchesthe unit off. The battery voltage data are also used to compensate for batteryvoltage changes that can affect printout quality.
9.6.12 Battery Type
The battery type circuit is illustrated in Figure 9-31.
BAT_TYPE
1N914CR27
150KR101TEST
TP2
15K
R100VRECHARGE
VCC
N-20AUXPCB
Figure 9-31: Battery Type Circuit
The unit operates on disposable batteries. Battery type input is digital; a highinput informs the CPU that rechargeable batteries are in use. If rechargeablebatteries are used, the battery and the VRECHARGE terminals are mechanicallyconnected. This applies the battery voltage to VRECHARGE, pullingBAT_TYPE high. R100 and CR27 are a current-limiting resistor and avoltage-clamping diode that are used to protect the input port from excessivebattery voltage. If disposable batteries are used, VRECHARGE is electricallyisolated, which allows R101 to pull BAT_TYPE input low.
Technical Supplement
9-29
The nominal voltages and voltage discharge curves are significantly differentbetween rechargeable and disposable batteries. In order for the CPU to predicthow much “battery life” remains, the nominal voltage and discharge curves mustbe known; the BAT_TYPE signal provides that information
9.6.13 Printer Control
Printer circuitry is divided into two subsections: the printer interface and theprinter flex circuit.
• Printer interface circuit (auxiliary PCB) — This circuit detects thepresence of the flex circuit, and supplies power to the print heads and paperadvance motor. Noise generated by the printer motor is filtered. Thecircuitry is protected from excessive battery currents by a fuse.
The printer interface circuit is illustrated in Figure 9-32, at the end of Section 9.
• Printer flex circuit — The printer flex circuit is added when the printer ispresent. The printer generates a timing signal that is read by the CPU andsent to the flex circuit. This circuit signals the CPU that a printer is presentby connecting one CPU input to ground. Power and power control signalsfrom the auxiliary PCB generate an output load for a resistor array; heatfrom this process produces a dot matrix pattern on thermal paper.
The printer flex circuit is illustrated in Figure 9-33, at the end of Section 9.The printer control block diagram is shown in Figure 9-6.
User control is provided by momentary push buttons: ON (on/off), ADV(advance), and D/D (day/date). ON enables or disables the printer, ADV controlsthe advance of printer paper, and D/D sets date, time, and other clockparameters.
When a low battery voltage condition is present, the N-20PA adjusts power tothe printer’s head; however, a weak battery voltage condition causes the printerto shut off, thereby allowing the N-20PA to continue to display oxygensaturation and pulse rate readings until the batteries are exhausted. An ambienttemperature sensor adjusts printout quality to compensate for environmentalconditions.
9.6.13.1 Printer Interface Circuit
The printer interface circuit is illustrated in Figure 9-32, at the end of section 9.
The following is a description of the printer interface circuitry found on allN-20PA auxiliary PCBs.
The CPU reads the PR_PRESENT signal to determine if a printer is installed.With PR_PRESENT left floating, it is pulled high by the weak pull-up resistorinside the CPU. If a printer is installed, PR_PRESENT is connected to switchedground, which causes a low input to the CPU. The optional printer circuit isprotected from excessive battery currents by fuse F2. CR28 is used to blocknoise generated by the printer motor being injected onto the batteries.
The N-20PA printer is a 16-character-wide thermal dot matrix printer, whichgenerates a CPU interrupt for every dot column. The thermal energy given to theprint head is controlled by the pulse width of the active high signals PR_DOTx.In order to provide consistent print quality, the ambient temperature, print drivevoltage, and print head resistance must be measured and accounted for.
Technical Supplement
9-30
Inside the print head are seven resistors that heat up when power is applied, andin turn create dark dots on the thermal paper. One lead of the print-headresistors is connected to the printer supply voltage VPRN; the other lead isconnected to the driver chip (see “Optional Printer Flex Circuit with UserControls”). One of the print dot resistor leads (DOT4) is also fed back to theprinter interface circuitry. The DOT4 signal is a print dot resistor with a rangeof 11-16 ohms, which is connected to VPRN.
The print head resistance is measured by U36. R143, R144, R145, R146, andhead resistor DOT4 form a two-level resistor bridge. The resistor bridge isswitched on when PR_MEAS is pulled high, pulling TP77 low and biasing theresistor bridge. The logic outputs of PR_HEAD1 and PR_HEAD2 are read in bythe CPU to determine the head-resistance category of this particular head. R156ensures that Q20 does not switch on when the batteries are installed backward.Due to the large current draw of the resistor bridge and the fact that the headresistance does not change significantly over time, the head resistance is onlymeasured once at every power-on.
The CPU starts the printer motor running by setting PR_MOTOR high. A singlemotor drives both the print head and paper advance mechanisms. The printerprovides a printer timing generator (TG) signal, which is an AC waveform ofabout 4 Vpp. Q19, R106, R142, and CR29 convert the AC waveform to aCMOS level square wave; this signal (PR_TACH) is then used as a CPUinterrupt line. An interrupt routine services the printer, thereby producing therequired dot patterns to create the characters. C127 is used to filter noise.
The position of the print head is sensed by the signal PR_HOME. Whenever theprint head is not in the home position, a switch in the printer closes, shortingPR_HOME to switched ground. Whenever the print head is in the homeposition, the switch opens, allowing R118 to pull PR_HOME high.
The print head dot pattern and pulse width are controlled by the CPU. Theproper printer dot values are loaded into the output port, then the proper pulsewidth is loaded into the CPU CAM for PR_STROBE. The signal PR_STROBEenables the outputs for the specified pulse width. When the PR_DOTX lines arehigh, a dot will be printed.
9.6.13.2 Printer Flex Circuit and User Controls
The printer flex circuit is illustrated in Figure 9-33, at the end of section 9.
The thermal printer is plugged in via connectors JP10 and JP11. ThePR_PRESENT signal is connected to switched ground to tell the CPU that aprinter is installed. U1 is a Darlington pair driver chip that is used to drive theprinter dots and motor. When an input is high, the output is shorted to ground,driving the output load.
The auxiliary PCB provides constant power (VPRN) and a power control line(PWR_ON). Q1 is used as a power control FET. Both halves are used inparallel to reduce the on resistance. When PWR_ON is high, the sources (S1,S2) short to the drains (D1, D2), connecting ground to U1 and C3. PWR_ONalso controls the regulated power supplies; thus, Q1 and the power supplies areboth enabled and disabled at the same time.
Technical Supplement
9-31
The large bulk capacitor C3 is required due to the large current spikes that arerequired by the printer and the large internal series resistance of disposablebatteries. Bulk capacitance is required to lessen the battery voltage drop causedby the current spikes.
The N-20PA has three additional user-control buttons. L8, L9, L10, C120,C121, and C122 provide ESD protection. R103, R104, and R105 providepull-ups when the user buttons are open. These pull-up resistors are in theprinter interface circuit to ensure that the buttons (ON, ADV, and D/D) are neverleft floating, regardless of whether an optional printer flex circuit is installed ornot.
The optional user controls consist of three momentary push-button elastomericcontact switches. Pull-up resistors are provided by the printer interface circuitry.R1, R2, and R3 help protect the input port by providing some current-limitingcapability. C4, C5, and C6 debounce the switch contacts.
9.7 CIRCUIT ILLUSTRATIONS
The foldout graphics referenced throughout the Technical Supplement text are asfollows:
Figure 9-8: LED Drive Circuit
Figure 9-10: N-20PA HSO Timing Diagram
Figure 9-13: AC Variable Gain Control Circuit
Figure 9-15: CPU Circuit
Figure 9-20: Output Port Circuit
Figure 9-23: Display Control Circuit
Figure 9-25: Power Supply Circuit
Figure 9-26: Power Control Circuit
Figure 9-32: Printer Interface Circuit
Figure 9-33: Printer Flex Circuit
Figure 9-34: N-20PA Main PCB Schematic Diagram
Figure 9-35: N-20PA Auxiliary PCB Schematic Diagram
Figure 9-36: N-20PA Flex Circuit Schematic Diagram
(This page intentionally left blank)
9-33
Figure 9-8LED Drive Circuit
TO CENTER MTG. HOLE
TP48
6.04KR18
.01UFC5
RSENS
MMBTA06
Q2
2N3904Q510K
R47
IR/RED
1N914
CR181N914
CR12
22PFC123
100K
R162
100K
R49
20KR44
.022UF
C38
.1UFC37
LT1013
U9A
2
6
7 8
1 280KR423.74K
R135
4.7PF
C60
182KR5020K
R43
.022UF
C39.1UF
C53
VCC
VCC
100K
R53
100K
R52
.1UFC36
MMBTA56Q3
6.8R54
10KR48MMBTA06
Q1
MMBTA56Q4
22.1K
R51
TP50
TP46
LED DRIVE
10KR46
10K
R64
.1UF
C55
4053
U10
7VEE
8VSS
16VDD
4Z
15Y
14X
9C
10B
11A
6INH
3Z1
5Z0
1Y1
2Y0
13X1
12X010K
R45
VCC
100PF
C118
100PF
C119
100PF
C117
100PF
C116
L5
L3
L4
TP45
TP47
SENSORINPUT
VREF
VREF
DB9F
P1
1 6 2 7 3 8 4 9 5
TP77
TP83
TP84
RSENS
LED DIS
OFF/ON
IR/RED
PHOTOI
PWM1PWM2
9-35
Figure 9-10N-20PA HSO Timing Diagram
OFF/ON(HSO.1)
/SAMPIR(HSO.2)
/SAMPRED(HSO.0)
IR/RED(P1.1)
µS
State Time
0
0
105.6
66
158.4
99
177.6
111
283.2
177
336.0
210
337.2
211
443.2
277
496.0
310
515.2
322
620.8
388
673.6
421
-60µS-60µS
9-37
Figure 9-13AC Variable Gain Control Circuit
15KR5
3.32K
R33
3.32K
R21
TP59
TP58
TP57
.47UFC31
.1UF
C30
IRAC
REDLED/AV
/ZERO
IRDC
.01UFC8
PWM0
12.1K
R31
3.32KR66
3.32KR61
LMC6044
U7D
14 13
12
LMC6044
U7B 7
6
5
34.8K
R37
100K
R36
.01UF
C111
.01UFC57
1NF
C32VREF
LTC201U11D
7
68
.015UFC29
15KR41
12.1K
R22
RED
3.32K
R60
3.32K
R29
47.5KR40LMC6044
U7C 8
9
10
LMC6044
U7A
11
4
12
3
34.8K
R28
100K
R30
1NFC28
VREF
LTC201U11C
.015UFC9
TP56
TP55.47UFC27
.01UFC56
.1UF
C58
4053
U3
7VEE
8VSS
16VDD
4Z
15Y
14X
9C
10B
11A
6INH
3Z1
5Z0
1Y1
2Y0
13X1
12X0
VCC
PWM1
.1UFC26
REDAC
3.32K
R20
TP54
.01UF
C61
REDLED/AV
IRLED/AV
REDDC
.01UFC7
+5.7
3.32K
R67
LTC201U11A
LTC201U11B5
41
16
VCC
+
+
TP76
TP86
TP85
11
10
9
2
13
From U2 pin 3
IR
BUSTO CPU
Figure 9-15CPU Circuit
1N914CR10
2N3904
Q22
15KR156
15KR73RST
VCC
.1UF
C65
TP42
TP41
RESET GENERATION
100KR72
VCC
22PF
C8922PF
C88 10KR75
10KR76
10MHz
Y2
AD0
WRRD
BAT_VOLT
ALE
RAMEN
DISP_LATCH
PR_PRESENT
10K R131 VCC
LEDDIS
PWR_DOWN
PR_TACHPR_TEMP
RST
VCC
EATXDRXD
NMI
AD15AD14AD13AD12AD11AD10AD9AD8AD7AD6AD5AD4AD3AD2AD1
IR/RED
OFF/ON
PWM1
IRLED/AV
SAMPIR
SAMPRED
PWM0
PWM2
TP4
RST
10KR137
CPU
/ZERO
80C196KC
U31
53AD7/P3.7
54AD6/P3.6
55AD5/P3.5
56AD4/P3.4
57AD3/P3.3
58AD2/P3.2
59AD1/P3.1
60AD0/P3.0
61RD
62ALE/ADV
66XTAL2
16RESET
2EA
9ACH7/P0.7
8ACH6/P0.6
10ACH5/P0.5
11ACH4/P0.4
4ACH3/P0.3
7ACH2/P0.2
5ACH1/P0.1
6ACH0/P0.0
12ANGND
13VREF
14GND
15EXTINT/P2.2
67XTAL1
52AD8/P4.0
51AD9/P4.1
50AD10/P4.2
49AD11/P4.3
48AD12/P4.4
47AD13/P4.5
46AD14/P4.6
45AD15/P4.7
3NMI
65CLKOUT
64BUSWIDTH
63INST
43READY
41WRH/BHE
40WRL/WR
18TXD/P2.0
17RXD/P2.1
39P2.5/PWM0
37VPP
19P1.0
20P1.1
21P1.2
22P1.3/PWM1
23P1.4/PWM2
30P1.5/BREQ
31P1.6/HLDA
32P1.7/HOLD
35HSO3
34HSO2
29HSO1
28HSO0
27HSI3/HSO5
26HSI2/HSO4
25HSI1
24HSI0
38P2.7/T2CAPT
33P2.6/T2U-D
42T2RST/P2.4
44T2CLK/P2.3
VREF
PR_HEAD2PR_HEAD1
DISP_PHASEPR_STROBE
PHOTOI
REDLED/AV
RSENS
REDDC
IRACIRDCREDAC
AMB_LIGHT
9-39
9-41
Figure 9-20Output Port Circuit
150K
R154 150K
R153150K
R152 150K
R151150K
R150 150K
R149150K
R148
74HC574
U17
1OC
11CLK
12Q8
9D8
13Q7
8D7
14Q6
7D6
15Q5
6D5
16Q4
5D4
17Q3
4D3
18Q2
3D2
19Q1
2D1
AD15AD14AD13AD12AD11AD10AD9AD8
150K
R123VCC
RTC_IO
PR_STROBEEXOUTEN
EX_OUT MSB
PR_DOT6PR_DOT5PR_DOT4PR_DOT3PR_DOT2PR_DOT1PR_DOT0
74HC574
U18
1OC
11CLK
12Q8
9D8
13Q7
8D7
14Q6
7D6
15Q5
6D5
16Q4
5D4
17Q3
4D3
18Q2
3D2
19Q1
2D1
TP82TEST
DISP_CLK
EXOUTEN
R132150K
EX_OUT LSB
RTC_CLKRTC_RSTPR_MOTOR
BEEP_2BEEP_1PR_MEAS
DISP_DATA
AD7AD6AD5AD4AD3AD2AD1AD0
9-43
Figure 9-23Display Control Circuit
HDR 7
JP5
7654321
EL DRIVE
VCC
HDR 32
JP3
3231302928272625242322212019181716151413121110987654321
VCC
SI9530
U20
18DOUT
26SL
20OSCIN
21OSCOUT
22POL
23LATCH
25CLK
27DIN
28VPP
24VDD
19GND
29BP
30O32
31O31
32O30
33O29
34O28
35O27
36O26
37O25
38O24
39O23
40O22
41O21
42O20
43O19
44O18
1O17
2O16
3O15
4O14
5O13
6O12
7O11
8O10
9O9
10O8
11O7
12O6
13O5
14O4
15O3
16O2
17O1
TEST
TP80
VCC
VDISP
DISP_CLK
DISP_DATA
HDR 32
JP2
3231302928272625242322212019181716151413121110987654321
DISPLAY DRIVERSVCC
SI9530
U19
18DOUT
26SL
20OSCIN
21OSCOUT
22POL
23LATCH
25CLK
27DIN
28VPP
24VDD
19GND
29BP
30O32
31O31
32O30
33O29
34O28
35O27
36O26
37O25
38O24
39O23
40O22
41O21
42O20
43O19
44O18
1O17
2O16
3O15
4O14
5O13
6O12
7O11
8O10
9O9
10O8
11O7
12O6
13O5
14O4
15O3
16O2
17O1
DISP_DL
DISP_POL
6.19KR117
MMBT5551LQ21
MMBT5401LQ14
1%182R95
1%182R93
390PF
C87
390PF
C8310KR116
VDISP
+70V
VCC
12.1K
R114
475K
R115
4.75KR113
MMBT5551LQ12
2N3904Q13
TALIQ COLD SWITCH +70V
DISP_PHASE
DISP_DL
DISP_POL
74HC74
U34
7GND
8Q2
9Q2
6Q1
5Q1
14VCC
13RST2
11CLK2
12D2
10SET2
1RST1
3CLK1
2D1
4SET1
VCC
RST
DISPLAY PS CTRL
9-45
Figure 9-25Power Supply Circuit
+
22UFC82
120UH
L2
22UF
C90
LT1172
U26
5VIN
6E1
7VSW
8E2
3FB
2VC
1GND
MURS110CR31
MURS110CR16
MURS110CR30
5367A
CR25
R119
3.32K
R96
43V 10%5W
50V4.7UFC113
50V1UF
C112
0.1UF
C85
2N3904
Q8
TESTTP38
100V.1UFC124
1%390KR125
1%390KR126
1%14KR127
+70V
50V2.2UFC95
50V2.2UFC92
RAW10V
RAW-5V
RAW12V
130T3
CR20130T3
CR19
130T3
CR15
130T3CR14
22.1K
R120
22UFC125
31.6KR86
.47UF
C78
22UFC71
2N3906
Q9
2.2UFC96
22UFC79
.1UFC72
.1UF
C81
130T3
CR13
22UF
C119
22UF
C118
22UF
C70
LT1054CS
U23
14V +
13OSC
12VREF
11VOUT
6CAP -
5GND
4CAP +
3FB/SD
0.1UFC75 28.7K
R83
BATT PLUS
BATTERY INPUT
BATT GND
10KR155
SI9956DY
Q15 5
D2 6
D2
7D1
8D1
4G2
3S2
2G1
1S1
1.5A
F1
TEST
TP3
TEST
TP1
10V
TRANZORB
CR24
TO CENTER MOUNTING HOLE
22UFC117
22UFC116
22UFC74
0.1UFC73
VBAT
150
R134
120UH
L1
1M
R77
POWER SUPPLY
100KR82
LT1173
U22
5GND
6AO
7SET
8FB
4SW2
3SW1
2VIN
1ILIM
SI9405DY
Q17
5DRN
6DRN
7DRN
8DRN
4GATE
3SRC
2SRC
100PF
C76
100KR85
10K
R84
VCC
9-47
Figure 9-26Power Control Circuit
JP18
9
8
7
6
5
4
3
2
1
L11
PWR_DOWN
GO_SW
3.32K
R81
475KR110
0.1UF
C110
TESTTP73
TESTTP71
100PF
C123
0.1UFC67
VCON
1N914
CR11
TEST
TP84
LT1046
Q15
3
6 8
2
TESTTP83
0.1UFC68
PWR_ON
VCON
3.32KR79
15KR102
TEST
TP72
74HC74
U21
7GND
8Q2
9Q2
6Q1
5Q1
14VCC
13RST2
11CLK2
12D2
10SET2
1RST1
3CLK1
2D1
4SET1GO_BTN
VCC
.01UFC66
VCONVCON
150KR78
MAIN PCBTO: N-20
GO BTN
JP9
PIN 17
VBAT
9-49
Figure 9-32Printer Interface Circuit
1KR156
100pf
C127
130T3
CR28
VBAT
1A
F2
TESTTP31
0.1UFC115
VPRN
150K
R105
100PF
C122
100PF
C121
100PF
C120
L10VCC
VCC
TESTTP34
TESTTP33
TESTTP32
DD
ADV
TESTTP30
TESTTP29
PR_DOT4
PR_DOT3
PR_DOT2
PR_DOT1
PR_DOT0
PWR_ON
ON_OFF
PR_PRESENT
VPRN
PR_MOTOR
TESTTP28
TESTTP27
TESTTP26
TESTTP25
TESTTP24
TESTTP23
150K
R103150K
R104
L9
L8
VCC
1N914
CR29
3.32K
R147 1K
R141
150K
R142
2N3904
Q19
PR_MEAS
150K
R106
VCC
150K
R118
VCC
PR_HEAD2
VPRN
PR_HOME
PR_TACH
60.4KR145
TESTTP77
TESTTP36
TESTTP352N3904
Q20
TESTTP37
PR_DOT6
PR_DOT5
VPRN
VPRN
22 HDR
JP9
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
DOT4
TG
HM
TO PRINTER PCB
TEST
TP79
14.0KR143
1.24KR144
TESTTP78
59
R146
VPRN
LT1017CS
U36A
6
41
3 4
5
LT1017CS
U36B13
12
11
PR_PRESENT
VPRN
PR_HEAD1
ADV BTN
DD BTN
ON BTN
9-51
Figure 9-33Printer Flex circuit
0.01uFC6
S3
1K
R3
DAY/DATE BUTTON
DD
ADV
ON_OFF
PR_PRESENT
0.01uFC5
0.01uFC4
S2
1K
R2
ADVANCE BUTTON
S1
1K
R1
ON OFF BUTTON
3300UF
C3
SI9956DY
Q1
5D2
6D2
7D1
8D1
4G2
3S2
2G1
1S1PWR_ON
PR_DOT1
PR_DOT0
PR_MOTOR
PR_DOT6
PR_DOT5
PR_DOT4
PR_DOT3
PR_DOT2
LB1256
U1
9GND
12OUT6
13OUT5
14OUT4
15OUT3
16OUT2
17OUT1
18OUT0
11OUTM
10VCC
7IN6
6IN5
5IN4
4IN3
3IN2
2IN1
1IN0
8INM
DOT0DOT1DOT2DOT3DOT4DOT5DOT6DOT6
HEADER 8
JP11
87654321
PRINTER
MTP102-16
SEIKO
M+M-
HM
TG
HEADER 6
JP10
654321
VPRN
22 HDR
JP9
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
DOT4
TG
HM
TO N-20 AUX BOARD
9-53
Figure 9-34N-20PA Main PCB Schematic Diagram
3.32K
R20
OFF/ON
6R160
LF444
U1D
LTC201
8
88.7KR158
12VREF
390PFC40 R2
13
ACROSS U6-5V
TANT
SUPPLY
22UFC21
+12V 1M
R23
6
51.1K
.1%
3
414
14
15
7U6D
LT1097
4 81
-5V 16
.1UF
C35
8
7
VCC
-5V
VREF
2.0KR63
2 -5V
+12V
88.7K
U357 5
+12V .1%
R159
TP78
ACROSS U35SUPPLY
TANT.1UF
C124
ACROSS U11 16.1UF
100K
.12UF
1
1NF
C331312X1
X X0
Z
Y
Y1Y0
2
2N3906
9
Q6
U1C
220PFC126
VREF
91011
VSSZ1Z0
INHVEE
VDD CBA
3 5
6
U2
47.5K
R39
100K
R7
.12UF100K
14
15
OP490SO
U4D16
100K
R9
C16R6
TP81
OP490SO
10R8
11
12
U4C
.015UFC9
C13
SUPPLY-5V
3
LMC6044
11
2 1
3.32K
R29
1NFC28
U7A
+5.7
4
41
3.32K
R67
TP883
-5V
.1UF
C125
VREF
+12V
C12222UFC23
TANT
+12V VCC
5LTC201
U11BLTC201U11A2
1 REDLED/AV
.47UFC26
.1UF
+C27
TP55
REDAC
.01UF
C61C7.01UF
TP87 TP53
IRLED/AV
TP54
REDDC
SAMPRED
OFF/ONSAMPIR
PWM2
TP75
2.2MR68
33.2KR136
3.32K
R26
TP89
.068UF
100K100K 4
TP52
1NF
.47UF
82.5K
R24
R27
3.32KC25
C34 2N3906
5
6
LF444
U1B
7
-5V
.068UF
100K
R10
C17
.12UF 2
3
100K
OP490SO
31
U4A 1
R12
TP5182.5K
VREF
C24.47UF
R254053
Q7 220PFC127
VREF
LF444
10 8
+12V
.068UF
C18R11
C15C14
12.1K U7C
.12UFC19 15K
R41
TP85LMC6044
8
47.5KR40
9 10 11 6
3 5
9
1N914CR3
1N914
CR1 VREF
LTC20110
R22
11U11C
VREF34.8K
R28
3.32K
R60
100K
1 2
13 12
R30
.1UF
C58
VCC4053
INH
CBA VEE
VDD
Z1Z0
VSS
7
16
8
TP57
TP56
X1
Y1Y0
Z
Y
U3
X0 X
4
15
14
PWM1
.01UFC56
.01UF
VTB8442BD8
C63
MMBTA13LQ8
LIGHT SENSORVCC
VCC
TP72
3.57KR135
2N3906Q25
LED DRIVE
DB9F
P1
L-8
MMBTA56
.1UF
C55
100PF
11
TP45 4
100PF
C116
TP47
L5
L3
2
1 6
7 3 8
L4
100PF
C117 C118
TP44SENSOR
L2L1
INPUT
9 5
LTC201U6C
10
VREF
3.32K
-5V
LF444
Q4MMBTA56
10K
TP50
TP46
R64
Q1
MMBTA06
R51
10KR48
10K
VREF
VCC
Q3
R4610K
.047UFC22
511KR157
2
R45
LTC201U6B
15
61
14
4
18PFC1
9 11
3.32K
182K
R58
R1
U1A
1
+12V
R17 1M
280KR19
3 .047UFC59
TP49
LTC201
3U6A
2
1
.068UF
VCC
14 12
VEE
VSS
VDD
10 11
9 B
4053
C
AINH 6
13
1
Z1Z0
Y1
3 5
Y0
X1X0
2
8
16
7
.1UF
VCC
C53
4Z
15Y
X
LT1013
U9A
7
VREF
U106 R42
.1UFC36
.022UF
C39
2
8
1
100K
R53
4.7PF
20KR43
182KR50
TP83
280K
C60
8
1N914
C20CR4
1N914
VREF
TP90
CR2
VREF
12.1K
R31
LTC201
.015UFC29
6
7
U11D
OP490SO
U4B 6
5 7
R66.01UF
R37
1NF
LMC6044
U7B
6
C32
5 7
3.32K.01UFC57
3.32K
3.32K
R61
R33
100K
R36
C111C8
.47UF
.01UF
C30
.1UF+C31
/ZERO
TP59
TP58
IRAC
REDLED/AV
3.32K
R21IRDC
PWM0OFF/ON
VREF
R52
1. ALL RESISTORS 1/8W 1% UNLESS OTHERWISE SPECIFIED.
R124
NOTES:
TO CENTER MTG. HOLE
.1UF
RAW-5V
221
RAW12V221
R122
R121
TP62
C94 22UFC93
2N3904
TP61
-5V
.1UFC80 22UF
C91
+12V
VREF
22UFC95
RAW10V182
R123
100PF
.01UFC5
6.04K0.1%
R18
RSENS
TP48
TP60
2N3904Q23
TRIMVOUT
10K
R161
Q24
4 2
LT1021
GND
U32
VIN
+5.7
5 6
.1UFC6
1
R546.8
VREF
MMBTA06
22.1K
Q2
10KR47
1N914
.1UF.1UF.1UF
TP64
GNDTP70
C1222UF
22UFC11
TP63
IR/RED
2N3904Q5 TP77
C52C50 C51
100K
R162
100K
22UFC48
VCC
1N914CR18
.022UF
C38
100K
R49
22PF
CR12
C123
.1UFC37
20KR44
.1UF.1UF.1UF.1UF.1UF.1UF
C105C10222UFC49 C106 C107
15KR5
TP86
C109C108
34.8K 12
TP79
LMC6044
15.8K
R56
14C119 VREF TP84 13
U7D
R70SENSE1%
47.5K .01UFC62
VBAT
VOLTAGEBATTERY
TP73
BAT_VOLT
15.8K 1%
R69
RSENS
LEDDIS
LT1013
TP80
4
3
40.2K
5
U9B
OFF/ON
IR/RED
PHOTOI
R57 TP76
RXD
GND
Q2Q2
TXD
TALIQ PS CTRL
CPU
EXTINT/P2.2
AD0
AD7AD6AD5AD4AD3AD2AD1
60
57 58 59
53 54 55 56
PR_TACHACH7/P0.7
15
AD15AD14AD13AD12AD11AD10AD9AD8
RDWR
ALE
52 51 50 49 48 47 46 45
RDALE/ADV
GND
WRL/WR
VPP 62 61
41 40
14
37VCC
BAT_VOLTPR_TEMP
RSENS
REDDCREDAC
AMB_LIGHT
IRACIRDC
6
ACH6/P0.6ACH5/P0.5ACH4/P0.4ACH3/P0.3ACH2/P0.2ACH1/P0.1ACH0/P0.0
11 10
9 8
4 7 5
U31
ANGNDVREF
VREF
12 13
BUSWIDTH
R75
67XTAL1XTAL2RESET
CLKOUT
TXD/P2.0RXD/P2.1
EA
6616 2
NMI 365
1817
10KR76
10K
RST
TXDEA
RXD
NMI
TP65
TP4
10KR128
TP66
SAMPIR34
10K
P1.3/PWM1
READYINST 64
6343
P1.0P1.1P1.2
192021
P2.5/PWM0
P1.4/PWM2P1.5/BREQP1.6/HLDAP1.7/HOLD 31
222330
HSO3HSO2
3932
35
RAMEN
DISP_LATCH
R131
LEDDISIR/RED
VCC
PR_PRESENT
PWR_DOWNIRLED/AV
PWM1PWM2
PWM0
33
HSI3/HSO5HSI2/HSO4
P2.7/T2CAPTP2.6/T2U-D
26
HSO0HSO1 29
2827
HSI1HSI0 25
2438
T2RST/P2.4T2CLK/P2.3 42
44
REDLED/AV
OFF/ONSAMPRED
DISP_PHASEPR_STROBE
/ZEROPHOTOI
PR_HEAD2PR_HEAD1
VCC
RST
SET2
74HC74
VCC
RST2CLK2D2
14
13 11 12
U34
RST1CLK1D1SET1
3
10
1
2 4
Q1Q1
10KR137
DIGITAL SECTION
GO BUTTON
PR_PRESENT 7
4 HDR
JP1
4
100PF
C121C120
100PF
L7
BEADL6
3BEAD
VCC
21
PORT
SERIAL DATA
RAW-5V
RAW12V
DISP_POL
DISP_DL
RAW10V
PWR_DOWN
DISP_PHASE
DISP_DL
7
8 9
DISP_POL 6 5
20 HDR
20
19
18
17
16
15
VBAT
VCC
14
13
12
11
10
9
8
PR_STROBE
PR_HEAD2
PR_HEAD1
PR_TACH
GO_SW
221
R80
S2
AUX PCBJP8
6
5
4
3
2
1
TO: N-20
TEMP SENSOR
7TP41Q3D3 D2A2
ROMEN
A15A14A13A12A11A10A9A8A7A6A5A4A3A2
A0A1
TP11
LM35
3
TEMP
GND
PR_TEMP 2
C115.1uF
U5
VCC 1 VCC
TP19
TP22TP21 RD
TP20
TP15
TP18TP17TP16
TP14TP13TP12
AD8 19Q1
2D1 A8
10KR109
74HC573TP40
ALE 1 11
AD15AD14AD13AD12AD11AD10AD9
6
9 8 7
5 4 3
OCC
TP7
TP10
TP8TP9
TP5TP6
D8D7D6D5
Q8Q7Q6Q5
D4D3D2
Q4Q3Q2
15 A12
121314
A15A14A13
161718
A11A10A9
10KR108
TP39
ALE
AD7
1 11
9AD6AD5AD4AD3
8 7 6 5
OC
U33
74HC573
Q7D7
C
D8 Q8
D6D5D4
Q6Q5Q4
12 A713141516
A6A5A4A3
AD6A7 15 30
4 5 6 7 8 9
14
27C1024L
RD
VCCVCC
ROMEN
A15A14A13A12A11A10A9A8
O13A13
CE
43 2 22
PGMVPPOE
3
41 40
A15A14
O15O14
A9
39 38 37 36
A12A11A10
35 32 31
A8A7A6
O9
O12
O10O11
O8O7O6
1011
A14
A11A15
AD15AD14AD13AD12AD11AD10
AD7
AD9AD8
A14A15
A13A12
A10
WRRD
20
64K X 16 EPROM
VCC
TP43
A3
A6A5A4
A2A1
26
29 28 27
A5A4A3A2
25 24
U15
A1A0
19
O5O4O3O2
161718
O1O0 21
RAMEN
WRRD
A12A11A10A9A8A7A6A5A4A3
A10
CS1
22 27 26
OEWECS2
20
2 23
A12A11
A6
21 24 25 3
A9A8A7
4 5 6 7
A5A4A3
D6D7 19
D5D4D3
18171615
AD2
AD5AD4AD3
AD1AD0
10KR133
AD7AD6AD5AD4AD3
2N3904
Q22
RST
R134
VCC
15 1
12
DC00-DFFF
74HC10
TP71
U30B 3
5 4 6
74HC10
10K
U30C
74HC10
11 10 9
74HC138
G2BG2AG1
5 4 6
3C
2 BA
Y7
U30A
13 2 1
1011121314
Y3
Y6Y5Y4
Y2Y1Y0
7 9
ROMEN0000-DBFF
8
TP74
AUX PCB
RAMENE000-FFFF
AD10
AD9
AD8
AD7
AD6
AD5
AD4
AD3
AD2
AD1
AD0
U28
ADDRESS DECODING
1N914CR10
TP42
475KR156
475K
.1UF
R73
15
TO: N-20
20 HDR
20
19
18
17
16
EXINEN
EXOUTEN
14
13
12
11
10
9
8
RESET GENERATION
ADDRESS DEMUX
AD2AD1AD0
4 3 2
U13
D2D1
Q2Q1
171819
A2A1A0
8K X 8 SRAM
A2A1A0
22PF
U14
8 9 10
A1A0
D1D0
131211
10MHzC8922PF
C88
Y2
AD2AD1AD0
100KR72
VCC
AD15
AD14
AD13
AD12
AD11
C65
VCC
JP7
6
5
4
3
2
1
SpO2 ANALOG
9-55
Figure 9-35N-20PA Auxiliary PCB Schematic Diagram
VCC
R8410K
R85100K
C76100PF
SRC 2
SRC 3
GATE 4
DRN 8
DRN 7
DRN 6
DRN 5
Q17
SI9405DY
ILIM 1
VIN 2
SW1 3
SW2 4
FB 8
SET 7
AO 6
GND 5
U22
LT1173
R82100K
POWER SUPPLYR77
1M
L1
120UH
R134
150
VBAT
C73.1UF
C7422UF
C11622UF
C11722UF
TO CENTER MOUNTING HOLE
CR24TRANZORB
10V
VCC
TP1
TEST
TP3
TEST
F1
1.5A
S1 1 G1 2
S2 3 G2 4
D1 8D1 7
D2 6D2 5
Q15
SI9956DY
R15510K
BATT GND
BATTERY INPUT
BATT PLUS
VRECHARGE
TO: N-20
MAIN PCBR78150K
VCON VCON
C66.01UF
VCC
GO_BTNSET1
4
D1 2
CLK1 3
RST1 1
SET2 10
D2 12
CLK2 11
RST2 13
VCC 14
Q1 5
Q1 6
Q2 9
Q2 8
GND 7
U21
74HC74
R100
15K
TP2
TESTR101150K
TP72
TESTR102
15K
R793.32K
CR271N914
VCON
PWR_ON
C68.1UF
BAT_TYPE
TP83TEST
JP9PIN 17
TP84
TEST
R8328.7KC75
.1UF
FB/SD 3
CAP + 4
GND 5
CAP - 6VOUT 11
VREF 12
OSC 13
V + 14
U23
LT1054CS
C70
22UF
C118
22UF
C119
22UF
C81
.1UF
C72.1UF
C7922UF
C962.2UF
C7122UF
C78
.47UF
R8631.6K
C12522UF
R120
22.1K
RAW12V
RAW-5V
RAW10V
C922.2UF50V
C952.2UF50V
+70V
R12714K1%
R126390K1%
R125390K1%
C124.1UF100V
TP38TEST
C85.1UF
C1121UF50V
C1134.7UF50V
5W43V 10%
R96
3.32K
R119
22.1K
CR255367A
CR30MURS110
GND 1
2
FB 3
E2 8
VSW 7
E1 6
VIN 5
U26
LT1172
C90
22UF
L2120UH
C8222UF
VCC
R71150K
CHECK BATTERY
O1 17
O2 16
O315
O4 14
O513
O612
O711
O810
O9 9
O10 8
O11 7
O12 6
O13 5
O14 4
O15 3
O16 2
O17 1
O18 44
O19 43
O2042
O21 41
O2240
O23 39
O24 38
O2537
O2636
O2735
O2834
O2933
O3032
O3131
O3230
BP29
GND 19
VDD 24
VPP 28
DIN 27
CLK 25
LATCH 23
POL 22
OSCOUT 21
OSCIN 20
SL 26
DOUT 18
U19
SI9530
VCCTALIQ DRIVERS
VCON
C67.1UF
C123
100PF
TP71TEST
TP73TEST
C110
.1UF
1234567891011121314151617181920212223242526272829303132
JP2
HDR 32
R110475K
R81
3.32K
GO_SW
PR_TACH
PR_HEAD1
PR_HEAD2
PR_STROBE
DISP_PHASE
PWR_DOWN
PR_PRESENT
DISP_DL
DISP_POL
L11
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
JP18
20 HDR
DISP_DATA
DISP_CLK
VCC
AD15
VBAT
RAW12V
RAW-5V
RAW10V
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
JP17
20 HDR
VDISP
VCC
TP80
TEST
AD0AD1AD2AD3AD4AD5AD6AD7
VCC
GO_BTN
BAT_BTN
ON_OFF_BTNDD_BTNADV_BTNPR_HOMEBAT_TYPE
R74
1KC64.01UF
RTC_IO
EX_IN INPUT PORT
SW1
L12
C126
100PF
TP88
TEST
D1 2
Q1 19
D2 3Q2 18
D3 4Q3 17
D4 5
Q4 16
D5 6Q5 15
D6 7
Q6 14
D7 8Q7 13
D8 9Q8 12
C11
OC 1
U16
74HC573
PR_HEAD1
VPRN
PR_PRESENT
TP81
TEST
11
12 13
U36B
LT1017CS
5
4 3
14
6
U36A
LT1017CS
DISP_PHASE
VPRN
R146
59
+70VTALIQ COLD SWITCH
Q132N3904
Q12MMBT5551L
R1134.75K
R115
475K
R11412.1K
TP78TEST
R1441.24K
R14314.0K
TP79TEST
VCC
+70V
VDISP
R11610K
C83390PF
C87390PF
R93182
1%
R95182
1%
Q14MMBT5401L
Q21MMBT5551L
R1176.19K
TO PRINTER PCB
HM
TG
DOT4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
JP9
22 HDR
VPRN
VPRN
PR_DOT5
PR_DOT6
TP37TEST
Q202N3904
TP35TEST
TP36TEST
TP77TEST
R14560.4K
PR_TACH
PR_HOME
VPRN
PR_HEAD2
VCC
R118150K
VCC
R106150K
PR_MEAS
Q19
2N3904
R142
150K
R141
1KR147
3.32K
BZ1
AT17
AD0AD1AD2AD3AD4AD5AD6AD7
DISP_DATA
PR_MEASBEEP_1BEEP_2
PR_MOTORRTC_RSTRTC_CLK
EX_OUT LSB
R132150K
EXOUTEN
EXINEN
DISP_CLK
TP82TEST
D1 2
Q119
D2 3 Q2 18
D3 4 Q3 17
D4 5
Q416
D5 6 Q5 15
D6 7
Q614
D7 8
Q713
D8 9
Q812
CLK 11
OC 1
U18
74HC574
O1 17
O2 16
O315
O4 14
O513
O612
O711
O810
O9 9
O10 8
O11 7
O12 6
O13 5
O14 4
O15 3
O16 2
O17 1
O18 44
O19 43
O2042
O21 41
O2240
O23 39
O24 38
O2537
O2636
O2735
O2834
O2933
O3032
O3131
O3230
BP29
GND 19
VDD 24
VPP 28
DIN 27
CLK 25
LATCH 23
POL 22
OSCOUT 21
OSCIN 20
SL 26
DOUT 18
U20
SI9530
VCC 1234567891011121314151617181920212223242526272829303132
JP3
HDR 32
AD3
AD4
AD5
AD6
AD7
AD8
AD9
AD10
AD11
AD12
AD13
AD14
AD0
AD1
AD2
EXINEN
EXOUTEN
TO: N-20
MAIN PCB
VCC
VCC REAL TIME CLOCK
PR_DOT0PR_DOT1PR_DOT2PR_DOT3PR_DOT4PR_DOT5PR_DOT6
EX_OUT MSB
EXOUTENPR_STROBE
RTC_IO
VCCR123
150K
AD8AD9AD10AD11AD12AD13AD14AD15
D1 2 Q1 19
D2 3
Q218
D3 4 Q3 17
D4 5
Q416
D5 6 Q5 15
D6 7 Q6 14
D7 8
Q713
D8 9
Q812
CLK 11
OC 1
U17
74HC574
R148
R149
150KR150
150K R151
150KR152
150K
BEEPER
TP74
TESTTP75TEST
VCC
L8
L9
R104
150K R103
150K
TP23TEST
TP24TEST
TP25TEST
TP26TEST
TP27TEST
TP28TEST
PR_MOTOR
VPRN
PR_PRESENT
ON_OFF
PWR_ON
PR_DOT0
PR_DOT1
PR_DOT2
PR_DOT3
PR_DOT4
TP29TEST
TP30TEST
ADV
DD
TP32TEST
TP33TEST
TP34TEST
VCC
VCCL10
C120
100PF
C121
100PF
C122
100PF
R105
150K
VPRN
C115.1UF
TP31TEST
F2
1A
RTC_CLKRTC_IO
RTC_RST
VBAT
R153
150KR154
150K
TP85
TEST
TP87
TEST
TP86
TEST
BT13V
Y1
32.768KHz
C114
.1uF
TP76
TESTSCLK
14
I/O12
RST 9
VCC 16
X1 3
X2 5
GND 8
U29
DS1202S
CR23
1N914
EL DRIVE
VCC
C99
.1UF
C100
.1UF
C101
.1UFC4922UF
1234567
JP5
HDR 7
C97
.1UF
C98
.1UF
DIGITAL IC'S BYPASS CAPS
C127
100pf
R156 1K
3.32KR163
+
VC
150K
LT1046
3
6
8
2
9-57
Figure 9-36N-20PA Flex Circuit Schematic Diagram
TO N-20 POWER SUPPLY BOARD
HM
TG
DOT4
JP9 VPRN
PR_DOT2
PR_DOT3
PR_DOT4
PR_DOT5
PR_DOT6
PR_MOTOR
PR_DOT0
PR_DOT1
10
11
12
13
14
15
16
17
18
19
20
21
22
1
2
3
4
5
6
7
8
9
22 HDR
ON OFF BUTTONR1
1K
S1
ADVANCE BUTTONR2
1K
S2
C40.01uF
C50.01uF
DAY/DATE BUTTONR3
1K
S3
C60.01uF
S1 1
G1 2
S2 3
G2 4
D1 8
D1 7
D2 6
D2 5
Q1
SI9956DY
PWR_ON
PR_PRESENT
ON_OFF
ADV
DD
INMIN0IN1IN2IN3IN4IN5IN6
VCC
OUTMOUT0OUT1OUT2OUT3OUT4OUT5OUT6
GND
U1
LB1256
C3
3300UF
8 1 2 3 4 5 6 7
10
1118171615141312
9
12345678
JP11
HEADER 8
DOT6DOT6DOT5DOT4DOT3DOT2DOT1DOT0
TG
HM
M-M+ 1
23456
JP10
HEADER 6SEIKO
MTP102-16
PRINTER