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r472C
15 MHz, TRIGGERED SWEEP
Du al -Trace Osclllosco1
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"o#aFF-'fiNPRTCE $3.00
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INSTRUCTION MANUAL
FOR
B & K.PRECISION
MODEL L472C15 MHz, TRIGGERED SWEEPDUAL.TRACE OSCILLOSCOPE
trIYNASCANCOF|POF|ATION
6460 West Corllqnd Streel
Chicogo, l l l inois 60635
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TABLE OF CONTENTS
INTRODUCTION
FEATURES
OPERATOR'S CONTROLS, INDICATORS AND FACILITIES
OPERATING INSTRUCTIONSInitial Starting ProcedureSingle ilrace Waveform ObservationCalibrated Voltage Measurement .Differential Voltage Measurement . .Calibrated Time Measurement .External Horizontal Input (X-Y Operation) . . . .Z-Axis InputDual-:Trace Waveform Observation .
SINGLE.T RAC E APPLI CATIONSIntroductionVideo Equipment ServicingSignal Tracing and Peak-to-Peak Voltage ReadingsComposite Video Waveform AnalysisSync Pulse AnalysisVITS (Vertical Interval Test Signal) . . . .
TELEVISION ALIGNMENTIntroductionImportance of Sweep Alignment . . .Sweep Adignment MethodsTuner AlignmentIF Alignment . .Chroma Alignment
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TABLE OF CONTENTS
FM RECEIVER ALIGNMENT . .
PHASE MEASUREMENT
FREQUENCY MEASUREMENT . . .
SQUARE WAVE TESTING OF AMPLIFIERSIntroductionTesting ProcedureAnalyzing the Waveforms
Page
. . . . . 3 5
35
37
. . . 3 7
. . . 3 8, . . 3 8
CIRCI.JIT DESCRIPTIONGeneralVertical PreamplifiersMode l,ogrcVertical AmplifierTrigger CircuitSync Amplifier and Inverter
CALIBRATION ADJUSTMENTSHousing Removal230 VAC OPERATIONGraticule RemovalAstigmatism AdjustmentCH A and CH B DC BalanceI12nd l/5 Attenuator BalanceHorizontal Position AdjustmentVertical Gain Adjustment
424242424242
44M4444444
47
48
WARRANTY SERVICE INSTRUCTIONS
WARRANTY
U
The B & K-hecision Model 1472C Triggered SweepDual-Trace Oscilloscope is a laboratory quality, professionalinstrument for observing and measuring waveforms inelectronic circuits. Dual vertical inputs are provided forsimultaneous viewing of two waveforms. Low-frequency,low repetition-rate waveforms are chopped at a 2OO kHz rateto provide for simultaneous viewing. Alternate sweep of thetwo inputs permits simultaneous viewing of high-speed,high repetition-rate waveforms. In addition, the sum or
DUAL TRACE Two input waveforms can beviewed either singly or simul-taneously, as desired. Individualvertical sensitivity and positioningcontrols are provided for com-pletely independent adjustment ofthe two signal amplitudes.
Only the cathode ray tube uses afilament. All other stages usetransistors, diodes, FET's (fielde f fec t transistors) and IC's.Among the advantages of solidstate construction are:
o No stabilization warm-uptime required.
o Low power drain.o Dependability -
reliabilityo Ruggedness.. Ught weight.o Compactness.
The 1472C's stability of waveformpresentations is beyond com-parison with non-triggered sweeposcilloscopes. The sweeps remainat rest until triggered by the signalbeing observed, to assure thatthey are always synchronized.Fully adjustable trigger thresholdallows the desired portion of thewaveforms to be used for trig-gering. A single waveform, or bothwaveforms in dual-trace opera-tion, can be synchronized to thesignal displayed on Channel A orChannel B or to an external synctrigger.
Thr 130 mm (approx. 5.1 inches)diameter cathode ray tube giveieasy-toread presentation on an 8x l0 cm rectangular viewing area.
difference of the two input waveforms can be displayed as asingle trace.
The dual-trace feature, together with the .15 MHzbandwidth, wide range of sweep speeds, and high sensitivityprovided, make this the ideal oscilloscope for. a broad rangeof applications, including troubleshooting'and repairiigelectronic equipment, research and development, and hbdratory instruction.
INTRODUCTION
FEATURES
\,
WIDE BANDWIDTH DC to 15 MHz bandwidth and 24nSEC rise time assure distortion-free, high-resolution presentationat high frequencies.
WIDE RANGE OF Sweep speed range of 0.5 pSEC/SWEEP SPEEDS cm to 0.5 SEC/cm provides every
speed necessary for viewing wave-forms from DC to 15 MHz.FULLY
SOLID STATE
TRIGGEREDSWEEP
LARGE SCREEN
CALIBRATEDSWEEP SPEED
Accurate time measurements onl9 different ranges.
E)(PANDEDSCALE
HIGHSENSITIVITY
VIDEO SYNC
VECTORSCOPE
CALIBRATIONSOURCE
ILLTJMINATEDSCALE
ZA)OSINPUT
A five time magnification (5X) ofthe horizontal sweep ailows close-up examination of a portion ofthe waveform. In addition, the 5Xmagnification provides a maxi-m um sweep sp eed o f 0 .1pSEC/cm.
Permits the low-capacitance, high-i m p e d a n c e , l 0 : l a t t e n u a t i o nprobes to be used for virtually allmeasurements, thus assuring lesscircuit loading.
A built-in sync separator circuit isincluded specifically for viewingtelevision signals. When usingVIDEO SYNC, vertical syncpulses are automatically selectedat sweep times of 0.5 SEC/cm to0.1 mSEC/cm for viewing tele-vision frames. Horizontal svncpulses are automatically seleciedat sweep times of 50 lSEC/cm to0.5 pSEC/cm for viewing televi-sion lines.
The unit may be used as a vector-scope to provide a color displayexactly as specified by color tele-vision manufacturers.
A built-in calibrated I volt peak-to-peak square wave permitschecking and recalibration of thevertical amplifiers without addi-tional equipment.
Fully variable illumination for thescale. Vertical and horizontdlmarkers on the scale make voltageand time measurements easy ioread.
Intensity modulation capabilityincluded for time or frequencymarkers.
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CALIBRATED Accurate measurement of theVOLTAGE SCALES instantaneous voltages on l l dif-
ferent attenuator ranges for bothChannel A and Channel B.
v
SPECIFICATIONS
b SWEEP CIRCLJITS (Common to CH A and CH B)
Deflection factor
bFrequency Response
Risetime
Overshoot
Input Resistance
Input Capacity
Tilt
Max. Input Voltage
Operating Modes
Ctrop Frequency
Channel Separation
Sweep System
Sweep Time
Sweep Range ofVariable Control
Sweep Magnification
Linearity
I*ngth of Sweep
TRIGGERING
Source
Slope
Triggering Range
0.01 V/cm to 20 V/cm, {%, in11 ranges each providing for fineadjustment.
DC: DC to l5 MHz (-3 dB)AC:2l7zto 15 MHz (-3 dB)
24 nanoseconds.
3% or less.
1 megohm (approximate).
22 pF (t3 pF).
I-ess than 5%.
300 V (DC + AC peak) or 600 VPP.
Channel A only.Channel B only.A & B (dual trace); trace automatically chopped at all sweeptimes of 1 mS/cm and slower;alte rnate trace automaticallyselected for all faster sweep times.A + B (single-trace algebraic sumof Channels A and B).A - B (single-trace algebraic dif-ference of Channels A and B).
200 krtz (nlV")Better than 60 dB.
Triggered and automatic. In auto-matic mode, sweep is obtainedwithout input signal.
0.SpSEC/cm to 0.5 SEC/cm(!sVo) in 19 ranges, in l-2-5 se-quence. Each overlapping rangeprovides for fine adjustment.
At least 2.5 times.
Obtained by enlarging the abovesweep 5 times from center. Maxi-mum swee p speed becomes0.1pSEC/cm.
3% or less distortion for 0.5SEC/cm to 2 pSEC/cm ranges.
5% or less for I pSEC/cm and 0.5pSEC/cm ranges.
102 mm to I l0 mm.
CH A, CH B and EXT: I V p-psensitivity.
P osi t ive and negat ive, con-tinuously variable level control;pull for AUTO.
20 Hz to 15 MHz (rnin. 0.5 cmdeflection as measured on cathoderay tube).
CALIBRATION VOLTAGE
I kHz square wave of I V p-p(!s%).
INTENSITY MODULATION
Vertical and horizontal syncseparator circuit provided so thatany portion of comPosite videowaveform can be sYnchronizedand expanded for viewing. LINE(hor iz) and FRAME (vert) sYncswitched automaticallY be SWEEPTIME/CM swltch.FRAME = 0.5 SEC/cm to 0. ImSEC/cm (vertical sYnc Pulse).LINE = 50 trtSEC/cm to 0.5 PSEC/cm (horizontal sync pulse).
10 mV/cm (nominal).
DC to 1 MHz (-3 dB).
I megohm (nominal).
22 pF (t3pF).
300 V (DC + AC peak) or 600 Vp-p.
With SWEEP TIME/CM switch inCH B position, the CH A inputbecomes the Y input (vertical)and the CH B input becomes theX input (horizontal). The CH Bposition control becomes thehorizontal position control.
120 VAC, 50/60 llz, 23 watts.(3-wire line cord, CSA-approvedfor oscilloscopes.)
108 to 132 VAC.
Variable illumination.
Carrying handle for tilt stand.
PR-35 (two required).
Combination 10:l and direct.
10 : l = l0megohms, l8 pF.Direct = I megohm, 120 pF.
BNC
Spring-loaded hook-on tip.
VERTICAL AMPLIFIERS (CH A and CH B) VIDEO Sync
HORIZONTAL AMPLIFIER (Horizontal input thru CH Binput)
Deflection Factor
Frequency Response
Input Resistance
Input Capacity
Input Protection
X-Y Operation
Voltagelnput Resistance
20 p-p minimum470 kO (nominal),+2OVo
POWER REQUIREMENTS
Input
Regulatron
MISCELLANEOUS
Scale
Mechanical Features
PROBESModel No.
Attenuation
Input Impedances
Connector
Tip
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1 1
1 0
1 2
v1 3
1 4
Fig. 1. Front panel controls and indicators.
OPERATOR'S CONTROLS. INDICATORS AND FACILITIES
b
1. Cathode Ray Tube (CRT). This is the screen on whichthe waveforms are viewed.
2. Scale. The 8 x l0 cm graticule provides calibrationmarks for voltage (vertical) and time (horizontal)measurements. Illumination of the scale is fully adjust-able.
3. POWER ILLUM control. Fully counterclockwise rota-tion of this control (OFF position) turns off oscillo-scope. Clockwise rotation turns on oscilloscope.Further clockwise rotation of the control increases theillumination level of the scale.
4. Pilot lamp. Lights when oscilloscope is turned on.
5. SWEEP TIME/CM switch. Horizontal coarse sweeptime selector. Selects calibrated sweep times of 0.5pSEC/cm (microsecond per centimeter) to 0.5 SEC/cmin 19 steps when VARIABLE control 6 is set to theCAL position (fully clockwise). In the CH B position,this switch disables the internal sweep generator andpermits the CH B input to provide horizontal sweep.
6. Sweep speed VARIABLE control. Fine sweep timeadjustment. In the extreme clockwise (CAL) positionthe sweep time is calibrated.
7. CAL lV P-P jack. Provides calibrated I kHz, I voltpeak-to-peak square wave input signal. This is used forcalibration of the vertical amplifier attenuators and tocheck the frequency compensation adjustment of theprobes used with the oscilloscope.
8. <>POSITION control. Rotation adjusts horizontalposition of traces (both traces when operated in thedual trace mode). Push-pull switch selects 5X magni-fication when pulled out (PULL 5X MAG); normalwhen pushed in.
9. TRJGGERING LEVEL control. Sync level adjustmentdetermines points on waveform slope where sweepstarts; (-) equals most negative point of triggering and(+) equals most positive point of triggering. Push-pullswitch selects automatic triggering when pulled out(PULL AUTO). When automatic triggering, a sweep isgenerated even without an input signal.
10. EXT TRIG jack. Input terminals for external triggersignal.
11. SYNC switch. Four-position lever switch with thefollowing positions:
SLOPE. The SLOPE positions are used for viewing allwaveforms except television composite video signals.
(+) Sweep is triggered on positive-going slope ofwaveform.
(-) Sweep is triggered on negative-going slope ofwaveform.
VIDEO. In the VIDEO positions, the sync pulsesof a composite video signal are used to triggerthe sweep; the vertical sync pulses (frame) areautomatically selected for sweep times of 0.5 SEC/cmto 0.1 mSEC/cm, and horizontal sync pulses (line) areautomatically selected for sweep times of 50 pSEC/cm
_ to .5 pSEC/cm.U
(+) Sweep is triggered on positive-going sync pulse.
(-) Sweep is triggered on negative-going sync pulse.
12. SOURCE switch. Three'position lever switch selectstriggering source for the sweep. Both sweeps aretriggered by the same source in dual trace operation.
CH A Sweep is triggered by Channel A signal.
CH B Sweep is triggered by Channel B signal.
EXT Sweep is triggered by an external signal appliedat the EXT SYNC jack 10.
13. Channel B POSITION control. Vertical position adjust-ment for Channel B trace. Becomes horizontal positionadjustment when SWEEP TIME/CM switch 5 is in theCH B position.
14. Channel B DC BAL adjustment. Vertical DC balanceadjustment for Channel B trace.
15. Channel B INPUT Jack. Vertical input jack of ChannelB. Jack becomes external horizontal input whenSWEEP TIME/CM switch 5 is in the CH B position.
16 Channel B DC-GND-AC switch.
DC Direct input of AC and DC component of inputsignal.
GND Opens signal path and grounds input to verticalamplifier. This provides a zero-signal base line,the position of which can be used as a referencewhen performing DC measurements.
AC Blocks DC component of input signal.
17. Channel B VOLTS/CM switch. Vertical attenuator forChannel B which provides step adjustment of verticalsensitivity. Vertical sensitivity is calibrated in l l stepsfrom .01 to 20 volts per cm when VARIABLE controll8 is set to CAL position. This control adjustshorizontal sensitivity when the SWEEP TIME/CMswitch 5 is in the CH B position.
18. Channel B VARIABLE control. Vertical attenuatoradjustment provides fine control of vertical sensivitity.In the extreme clockwise (CAL) position, the verticalattenuator is calibrated. This control becomes the finehorizontal gain control when the SWEEP TIME/CMswitch 5 is in the CH B Position.
19. MODE switch. Five'position lever switch; selects thebasic operating modes of the oscilloscope.
CH A Only the input signal to Channel A isdisplayed as a single trace.
CH B Only the input signal to Channel B isdisplaYed as a si4gle trace.
A & B Dual trace operation; both the Channel Aand Channel B inpuj signals are displayed ontwo seParatd traces.
A + B The waveforms from Channel A and ChannelB inputs are added and the sum is displayedas a single trace.
A - B The waveform from Channel B is subtractedfrom the Channel A waveform and thedifference is displayed as a single trace. Ifonly a Channel B input is present, thedisplay is inverted.
20. Channel A VOLTS/CM switch. Vertical attenuator forChannel A which provides coarse adjustment of verticalsensitivity. Vertical sensitivity is calibrated in I I steps
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21.
22.
from .01 to 20'volts per cm when VARIABLE control2l is set to the CAL position.
Channel A VARIABLE control. Vertical attenuatoradjustment provides fine control of vertical sensitivity.In the extreme clockwise (CAL) position, the verticalattenuator is calibrated.
Channel A Irc-GNDAC switch.
DC Direct input of AC and DC component ofinput signal.
GND Opens signal path and ground input tovertical amplifier. This provides a zero-signalbase line, the position of which can be usedas a reference when performing DC measure-ments.
AC Blocks DC component of input signal.
Channel A INPUT jack. Vertical input jack of ChannelA.
Channel A DC BAL adjustment. Vertical DC balanceadjustment for Channel A trace.
Channel A POSITION control. Vertical position adjust-ment for Channel A trace.
OPERATING
INITIAL STARTING PROCEDUREl. Set POWER ILLUM control 3 to OFF position (fully
counterclockwise).
2. Connect power cord 30 to a 120-volt, 50/60 Hz outlet.3. Set CH A POSITION control 25, CH B POSITION
control l3 and < > POSITION 8 to the centers of their.ranges.
4. Pull TRIGGERING LEVEL control 9 to the AUTOposition.
5. Set CH A DC-GND-AC switch 22 and CH BDC-GND-AC switch 16 to the GND positions.
ASTIG adjustment. Astigmatism adjustment providesoptimum spot roundness when used in conjunctionwith the FOCUS control 27 and INTENSITY control28. Very little readjustment of this control is requiredafter initial adjustment.
FOCUS control.
INTENSITY control. Adjusts brightness of trace.
Fuse holder.
AC line cord. CSA-approved for oscilloscopes.
INT MOD jack. Intensity modulation (Z-axis) input.
Combination carrying handle and tilt stand.
Probe (see Fig. 3). The B & K-Precision Model PR-35combination l0:1/Direct probe has been designed foruse with this oscilloscope. However, any probe de-signed for use with an oscilloscope having a nominalinput impedance of I megohm shunted by 27 pF andcapable of operation up to l5 MHz, can be used.
Vector Overlay (not shown). Interchanges with scalefor vectorscope operation.
26.
27.
28.
29.
30.
3 1 .
32.
33.
\,
23.
24.
25. 34.
6. &t the MODE switch 19 tosingle -trace operation or thedual-trace operation.
B position forB position for
7. Turn on oscilloscope by rotating the POWER ILLUMcontrol 3 clockwise. It will "click" on and pilot lamp 4will light. Turn control clockwise to the desired scale 2illumination.
8. Wait a few seconds for the cathode ray tube (CRT) towarm up. A trace (two traces if operating in the A & Bmode) should appear on the face of the CRT.
9. I f no trace appears, increase (clockwise) theINTENSITY control 28 setting until the trace is easilyobserved.
10. Adjust FOCUS control 27 and INTENSITY control 28for the thinnest, sharpest trace.
I l. Readjust position controls 8,25 and 13 if necessary, tocenter the traces.
12. Check for proper adjustment of ASTIG control 26, andDC BAL controls 14 and 24 as described in'theMAINTENANCE AND CALIBRATION portion of thismanual. These adjustments require checking onlyperiodically.
8
TNSTRUCTIONS
The oscilloscope is now ready for making waveformmeasurements.
CAUTION
Never allow a small spot of high brilliance toremain stationary on the screen for more than afew seconds. The screen may become permanentlyburned. Reduce intensity or keep the spot inmotion by causing it to sweep.
SINGLE-TRACE WAVEFORM OBSERVATION
Either Channel A or Channel B can be used forsingle-trace operation. The advantage of using Channel B isthat the polarity of the observed waveform can be reversedby placing the MODE switch 19 in the A-B position if thereis no input to Channel A. For convenience, Channel B isused in the following instructions.
1. Perform the steps of the "Initial Starting Procedure"with the MODE switch 19 in the CH B position. Thenconnect the probe cable to the CH B INPUT jack 15.The following instructions assume the use of theB & K-Precision Model PR-35 combination probes.
2. For all except low-amplitude waveforms, the probesare set for 10:1 attentuation. For low-amplitudewaveforms (below 0.5 volt peak-to-peak), set the probefor DIRect. See Fig. 3 for changing the probes froml0:1 to DIRect, or vice versa. The probe has a l0megohm input impedance with only 18pF shuntcapacitance in the 10: I position and 1 megohm with120 pF shunt capacitance in the DIRect position. Thehigher input impedance (low-capacity position) shouldbe used when possible, to decrease circuit loading.
3. Set CH B DC-GNDAC switch 16 to AC for measuringonly the AC component (this is the normal position foi
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the CHA &
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COMBINATION FEETAND CORD WRAP
Fig.2. Rear and side panel facilities.
U ;fffffff�,F ,ffi=- : *
\ PRoBE coMPENSATIoN1O:1 ADJUSTMENT
ATTENUATION
cLP- l8r tP 7
q,,
r>- 3. PUSH BACK ToGETHER r> -
C L P . 1 8 T I P
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Fig.3. Probe details.
most measurements and must be used if the pointbeing measured includes a large DC component). Usethe DC position for measuring both the AC componentand the DC reference, and any time a very lowfrequency waveform (below 5 Hz) is to be observed.The GND position is required only when a zero-signalgound reference is required, such as for DC voltagereadings.
4. Connect gound clip of probe to chassis ground of theequipment under test. Connect the tip of the probe tothe point in the circuit where the waveform is to bemeasured.
WARNING
a. If the equipment under test is a trans-formerless-Ae powered item, use an isolationtransformer to prevent dangerous electricalstrock.
as a smaller portion is displayed. This is because thesweep speed increases but the sweep repetit ion ratedoes not change.
NOTEWhen using very fast sweep speed at low repe.titionrates, the operator may wish to operate with theintensity control toward maximum. Under theseconditions, a retrace "pip" may appear at theextreme left of the trace. This does not in any wayaffect the oscilloscope operation and may bedisregarded.
10. After obtaining the desired number of waveforms, as instep 9, it is sometimes desirable to make a finaladjustment of the TRIGGERING LEVEL control 9.The (-) direction selects the most negative point onthe waveform at which sweep triggering will occur andthe (+) direction selects the most positive point on thewaveform at which sweep tri'ggering will occur. Thecontrol may be adjusted to start the sweep on anydesired portion of the waveform.
11. For a close-up view of a portion of the waveform, pulloutward on the < > POSITION control 8. This expandsthe sweep by a factor of five (5X magnification) anddisplays only the center portion of the sweep. To viewa portion to the left of center, turn the < > POSITIONcontrol clockwise, and to view portions to the right of@nter, turn the control counterclockwise. Push inwardon the control to return the sweep to the normal,non- magnified co ndition.
CALIBRATED VOLTAGE MEASUR-EMENT (See Fig. a)
Peak voltages, peak-to-peak voltages, DC voltages andvoltages of a specific portion of a complex waveform areeasily and accurately measured on the Model 1472Coscilloscope.
1. Adjust controls as previously instructed to display thewaveform to be measured.
2. k sure the CH B vertical VARIABLE control 18 is setfully clockwise to the CAL position.
3. Set CH B VOLTS/CM switch 17 for the maximumvertical deflection possible without exceeding thelimits of the vertical scale.
4. Read the amount of vertical deflection (in cm) fromthe scale. The CH B POSITION control 13 may bereadjusted to shift the reference point for easier scalereading if desired. When measuring a DC voltage, adjustthe CH B POSITION control 13 to a convenientreference with4he CH B DC-GND-AC switch 15 in theGND position, then note the amount the trace isdeflected when the switch is placed in the DC position.The trace deflects upward for a positive voltage inputand downward for a negative voltage input.
NOTEFor an accurate display of high-frequency wave-forms above l0MHz, it is important that (1) theprobe be used in the 10: I position to reducecircuit loading; (2) the oscilloscope controls be setso that the height of the pattern does not exceed 4cm; and (3) the trace be centered vertically.
5. Calculate the voltage reading as follows: Multiply thevertical deflection {in cm) by the VOLTS/CM controll7 setting (see example in Fig. a). Don't forget that thevoltage reading displayed on the oscilloscope is onlyl/l0th the actual voltage being measured when the
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b. The peak-to-peak voltage at the point ofmeasurement should not exceed 600 voltswhen using the DIRect position of the probe.
5. Set CH B VOLTS/CM switch 17 and the VARIABLEcontrol 18 to a position that gives 2to 6 cm (two tosix large squares on the scale) vertical deflection. Thedisplay on the screen will probably be unsynchronized.The Semaining steps are concerned with adjustingsynchronization and sweep speed, which presents astable display strowing the desired number of wave-forms. Any signal that produces at least I cm verticaldeflection develops sufficient trigger signal to syn-chronize the sweep.
6. Set SOURCE switch 12 to the CH B position. Thisprovides internal sync so that the Channel B waveformbeing observed is alqo used to trigger the sweep. Duringsingle trace operation on Channel A, the SOURCEswitch should be placed in the CH A position forinternal sync. Most waveforms should be viewed usinginternal sync. When an external sync source is required,the SOURCE switch should be placed in the EXTposition and a cable should be connected from theEXT TRIG jack l0 to the external sync source.
7. Set SYNC switch I I to the VIDEO (+) or (-) positionsfor observing television composite video waveforms orto the SLOPE(+) or SLOPE(-) positions for observingall other types of waveforms. Use the (+) position ifthe sweep is to be triggered by a positive-going wave, orthe (-) position if the sweep is to be triggered by anegative-going wave. If the type of waveform isunknown, the SLOPE(+) position may be used.
8. Readjust TRIGGERING LEVEL control 9 to obtain asynchronized display without jitter. As a starting point,the control may be pushed in and rotated to any pointthat will produce a sweep, which is usually somewherein the center portion of its range. The trace willdisappear if there is inadequate signal to trigger thesweep, such as when measuring DC or extremely lowamplitude waveforms. If no sweep can be obtained,pull the control out (PULL AUTO) for automatictriggering.
9. Set SWEEP TIME/CM switch 5 and VARIABLEcontrol 5 for the desired number of waveforms. Thesecontrols may be set for viewing only a portion of awaveform, but the trace becomes progressively dimmer
Y,
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probe is set for l0: 1 ittenuation. The actual voltage isdisplayed when the probe is set for DIRect measure-ment.
6. Calibration accuracy of this oscilloscope may beoccasionally checked by observing the I volt peak-to-peak square wave signal available at the CAL lV P-Pjack 7. This calibrated source should read exactly Ivolt peak-to-peak. If a need for recalibration is in-dicated, see the "MAINTENANCE AND CALIBRA-TION" section of the manual for complete procedures.
DIFFERENTIAL VOLTAGE MEASUREMENT (See Fig. 5)
This oscilloscope may be used to observe waveforms andmeasure voltages between two points in a circuit, neither ofwhich is circuit ground. Such measurements as the inputs toa differential amplifier, the output of a phase splitter orpush-pull amplifier, the amount of signal developed across asingle section of voltage divider or attenuator, and manyothers, require this technique.
l. Adjust controls as previously described under "Initial
Starting Procedure."
2. Connect a probe cable to both the CH A and CH BINPUT jacks 23 and 15.
Connect ground clips of the two probes to the chassisof equipment under test, and connect tips of theprobes to the points in the circuit where measurementsare to be made. It is usually desirable to connect theCH A probe to the higher potential or higher amplitudepoint in the circuit and the CH B probe to the lowerpotential or lower amplitude point in the circuit.
Set the MODE switch 19 to the CH A position and theSOURCE switch 12 to the CH A position and adjustthe controls as previously instructed in the "Single-
Trace Waveform Observation" procedure to obtain asynchronized single waveform of 2 to 6 cm verticalheight with the cH A VARIABLE control2l set to CAL.
If only the AC component of the waveform is ofinterest, use the following procedure:
^. Set CH A and CH B DC-GND-AC switches 22 andl6 both to the AC position.
b. Set CH B VARIABLE control 18 to CAL and theCH B VOLTS/CM switch 17 to the same positionas the CH A VOLTS/CM switch 20.
c. If the Channel A and Channel B inputs are inphase, set the MODE switch 19 to the A-Bposition. The displayed waveform is the peak-to-peak difference between the two points of meas-
3.
4.
5 .
b
. > P O S I T I O N C O N T R O L A D J U S T E D S O T H A TT O P O F W A V E F O R M C R O S S E S C E N T E R O FV E R T I C A L S C A L E M A R K E R F O R A C C U R A C YA N D E A S E O F R E A D I N G
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POSIT I ON CONTROL ADJUSTE DSO THAT BOTTOM OF WAVE.F O R M A L I G N S E X A C T L Y W I T HA H O R I Z O N T A L R E F E R E N C E L I N E
P c ? @ f l
VOLT9cmSET TO
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E X A M P L E :
V E R T I C A L D E F L E C T I O N = 4 . 2 c mV O L T A G E / C M = . O 2
.o84VP R O B E A T T E N U A T I O N = 1 O
P E A K - T O - P E A K W A V E F O R M = O € 4 V
1 0 : 1P R O B E A T T E N U A T I O N
Fig. 4. Typical voltage measurement.
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urement. If the waveform is small, the verticalsensitivity may be increased but the CH A and CHB VOLTS/CM switches must both be in the sameposition.
If the Channel A and Channel B inputs are 180"out of phase, such as the output of a push-pullamplifier, set the MODE switch 19 to the A-Bposition to measure the full peak-to-peak wave-form. Set the MODE switch to the A+B positionto measure any imbalance between the two pointsof measurement. Readjust the VOLTS/CMswitches 17 and 20 as required to obtain as large awaveform as possible without exceeding the limitsof the vertical scale, but always keep the CH A andCH B switches set to the same sensitivity.
Position the waveform as desired with thepositioning controls and calculate the peak-to-peakvoltage as described in the "Calibrated VoltageMeasurement" procedure.
6. If a DC voltage, or the DC component of the waveformis of interest, use the following procedure:
a. Set CH A DC-GNDAC switch 22 to the DCposition.
b. Position the CH A VOLTS/CM switch 20 to keepthe trace within the limits of the vertical scale.Use the CH A POSITION control 25 to align thetrace with one of the lines on the scale forreference.
c. Position CH B VOLTS/CM switch 17 to the sameposition as the CH A VOLTS/CM switch.
d. Set CH B DC-GNDAC switch 16 to the GNDposition and adjust out any error that may beintroduced by the Channel B positioning controlas follows: Alternately set the MODE switch l9 tothe A+B and A-B positions, adjusting the CH BPOSITION control 13 until the trace position doesnot shift as the MODE switch position changes.
e. Return CH B DC-GNDAC switch 16 to the DCposition.
f. Momentarily return the MODE switch 19 to theCH A position and note the trace position forreference. You may readjust it with the Channel Avertical positioning control, but not the Channel Bcontrol. Place the MODE switch in the A-Bposition. The amount of displacement of the tracefrom the Channel A reference represents thevoltage differential between the two points ofmeasurement.
CALIBRATED TIME MEASUREMENT (See Fig. 6)
Pulse width, waveform periods, circuit delays and allother waveform time durations are easily and accuratelymeasured on this oscilloscope. Calibrated time measure-ments from .5 second down to 0.1 microsecond arepossible. At low sweep speeds, the entire waveform is notvisible at one time. However, the bright spot can be seenmoving from left to right across the screen, which makesthe beginning and ending points of the measurement easyto spot.
1. Adjust controls as previously described for a stabledisplay of the desired waveform.
2. Be sure the sweep time VARIABLE control 6 is fullyclockwise to the CAL position.
3. Set the SWEEP TIME/CM control 5 for the largestpossible display of the waveform segment to bemeasured, usually one cycle.
4. If necessary, readjust the TRIGGERING LEVEL con-trol 9 for the most stable display.
5. Read the amount of horizontal deflection (in cm)be tween the points of measurement. The < >POSITION control 8 may be readjusted to align one ofthe measurement points with a vertical scale marker foreasier reading.
Calculate the time duration as follows: Multiply thehorizontal deflection (in cm) by the SWEEP TIME/CMswitch 5 setting (see example in Fig. 5). Remember,when the 5X magnification is used, the result mustbe divided by 5 to obtain the actual time duration.
Time meastirements often require external sync. This isespecially true when measuring delays. The sweep isstarted by a sync signal from one circuit and the
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E X A M P L E :
V E R T I C A L D E F L E C T I O N = 6 c mVOLTAGE/cm = .O2
1 . 2 V1 0PROBE ATTENUATION
PEAK-TO-PEAK WAVEFORM12V
Fig. 5. Typical differential measurement.
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Fig.6. Typical
waveform measured in a subsequent circuit. This allowsmeasurement of the display between the sync pulseand the subsequent waveform. To perform such meas-urements using external sync, use the following steps:
a. Set the SOURCE switch 12 to the EXT position.
b. Connect a cable from the EXT TRIG jack l0 tothe source of sync signal. Use a short shieldedcable.
c. Set the SYNC switch I I to the SLOPE (+) or (-)position for the proper polarity for the sync signal.
d. Readjust the TRIGGERING LEVEL control 9 ifnecessary for a stable waveform.
e. If measuring a delay, measure the time from thestart of the sweep to the start of the waveform.
8. Another excellent method for measuring time delays iswith dual-trace operation. The procedures are given inthe "DUALTRACE APPLICATIONS" section of themanual.
EXTERNAL HORTZONTAL rNpUT (X-y OPERATTON)
For some measurements, an external horizontal deflec-tion signal is required. This is also referred to as an X-Ymeasurement, where the Y input provides vertical de-flection and the X rnput provides horizontal deflection. Thehorizontal input may be a sinusoidal wave, such as for
time measurement.
phase measurement, or an external sweep voltage. Thisinput must be l0 mV per cm of deflection or greater; thusany voltage of 100 mV or greater is sufficient forsatisfactory operation. To use an external horizontal input,use the following procedure:
1. Set the SWEEP TIME/CM switch 5 fully clockwise tothe CH B position.
2. Use the Channel A probe for the vertical input and theChannel B probe for the horizontal input.
3. Adjust the amount of horizontal deflection with theCH B VOLTS/CM and VARIABLE controls 17 and 18.
4. The CH B (vertical) POSITION control now servesas the horizontal position control, and the <> POSI-TION control is disabled.
NOTE
Do NOT use the PULL 5X MAG control duringX-Y operation. Use the CH B VARIABLE andVOLTS/CM controls to adjust horizontal gain.
5. All sync controls are disconnected and have no effect.
H O R I Z O N T A LD E F L E C T I O N
6 .35c m
a >P O S I T I O N C O N T R O L A D J U S T E D S OT H A T L E A D I N G E D G E O F W A V E -F O R M A L I G N S W I T H A V E R T I C A L
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V A R I A B L Ese t to CALS W E E P T I M E / C Mset to 1 Opr sec
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C H B
R E F E R E N C E L I N E . E D G EM A Y N O T B E V I S I B L E O N V E R YF A S T P U L S E S ; I N T H I S C A S EA L I G N W H E R E V E R W A V E F O R MB E G I N S .
? @fi@nP O S I T I O N C O N T R O L A D J U S T E D S OT H A T T R A I L I N G E D G E O F W A V E F O R MC R O S S E S H O R I Z O N T A L S C A L E M A R K E RF O R A C C U R A C Y A N D E A S E O F R E A D I N G
E X A M P L E :
H O R I Z O N T A L D E F L E C T I O NS W E E P T I M E / C M
T I M E D U R A T I O N( o r P E R I O D ) O F W A V E F O R M
= 6 .35cm= I O p S E C= 63 .5pSEC
F R E O U E N C Y = 1 = 1TrME .0000635 SEC
= 15,75O Hz, D I S P L A Y S S H O W T Y P I C A L T E L E V I S I O N
R E C E I V E R W A V E F O R M A T G R I D O FH O R I Z O N T A L O U T P U T T U B E
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ZA)flS INPUT
The trace displayed on the screen may be intensitymodulated (Z-axis input) where frequency or time-scallma+s are requirgq. A 2Gvolt peak-to-peak or gteater signalapplied at-the INT MOD (intensity modulation) jack 3l onthe rear of the oscilloscope will provide alternate-brightnessand blanking of the trace. See Fig. 7.
DUAL{RACE WAVEFORM O BSERVATION(Refer to Fig. 8 )
In observing simultaneous waveforms on channels A andB, it is necessary that the waveforms be related infrequency or that one of the waveforms by synchronized tothe other although the basic frequencies hay be different.An- example of this is in checking a frequency divider ormult_iplier. The reference, or "clock" frequency can be usedon - Channel A, for example, and the- muliiple or sub-multiple of this referenie frequency will be dlsplayed onChannel B. In this Way, when the waveform display ofChannel A is synchronized, the display on Channei B willalso be in qync with the Channel A display. If twowavefor-ms having no phase or frequency reiationship toeach other are displayed simultaneously, it will be difficultif ngl impossible to lock both waveforms in sync for anyuseful observation.
To display two waveforms simultaneously for observa-tion, use the following procedure:
l. Perform the steps of the "Initial Starting procedure."
2. Connect oscilloscope probe cables to both the CH Aand CH B IMUT jacks 23 and 15.
3. If the recommended B & K-Precision Model PR-35oscilloscope probes are used, l0:l attenuation shouldbe used except for waveforms of 0.5 volt peak-to-peakor less. For the lower amplitude waveformi the Dlilectposition should be used. See Fig. 3 for changing theprobe from l0:1 to DIR or vice versa. Wheneverpossible, use the high impedance, low capacity l0: Iposition to minimize circuit loading.
4. Set MODE switch 19 to the A & B position. Two tracesstrould appear on the screen.
5. Adjust CH A and CH B POSITION controls 25 and 13to place the Channel A trace above the Channel Btrace, and adjust both traces to a convenient referencemark on the scale.
l 4
6. Set both the CH A and CH B DC-GNDAC switches 22and l6 to the AC position. This is the position used formost measurements and must be used if the pointsbeing measured include a large DC component.
7. Connect the ground clips of the probes to the chassisgr_ound of the equipment under test. Connect the tipsof the probes to points in the circuit where thewaveforms are to be measured. It is preferred that thesignal to which the waveform will be synchronized beapplied to the Channel A input.
WARNINGa. If the equipment under test is a transformer-
less AC unit, use an isolation transformer toprevent dangerous electrical strock.
b. The peak-to-peak voltage at the point ofmeasurement should not exceed 600 volts, ifthe probe is used in the DIR position.
8. Set the VOLTS/CM controls 17 and 20 for Channels Aand B to a position that gives 2 to 3 cm verticaldeflection. The displays on the screen will probably beunsynchronized. The remaining steps, although similarto those outlined for single-trace operation, describethe procedure for obtaining stable, synchronizeddisplays.
9. Set the SOURCE switch 12to the CH A position. Thisprovides internal sync so that the Channel A waveformbeing observed is also used to trigger the sweep. Ifdesired, the Channel B waveform may be used totrigger the sweep by setting the SOURCE switch to theCH B position. Often in dual-trace operation, a syncsource other than the measurement point for ChannelA or B is required. In this case set the SOURCE switchto the EXT (external) position and connect a cablefrom the EXT TRIG jack l0 to the sync source.
10. Set the SYNC switch 11 to the VIDEO (+) or (-)positions for observing television composite videowaveforms-, or to the SLOPE (+) or SLOPE (-)positions for observing all other types of waveforms.Use the (+) positions if the sweep is to be triggered bya positive-going wave, or to the (-) position if thesweep is to be triggered by a negative-going wave.
I 1. Adjust TRIGGERING LEVEL control 9 to obtain astable, synchronized sweep. As a starting point, thecontrol may be pushed in and rotated to any point thatwill produce a sweep, which is usually somewhere intlre center portion of its range. The trace will disappearif there is inadequate signal to trigger the sweep, iuchas when measuring extremely low amplitude signals. Ifno sweep can be obtained, pull out the control (PULLAUTO) for automatic triggering.
12. Set SWEEP TIME/CM switch 5 and VARIABLEcontrol 6 for the desired number of waveforms. Thesecontrols may be set for viewing only a portion of awaveform, but the trace becomes progressively dimmeras a smaller portion is displayed.
13. After obtaining the desired number of waveforms as instep 12, it is sometimes desirable to make a finaladjustment of the TRIGGERING LEVEL control 9.The (-) direction of rotation selects the most negativepoint on the sync waveform at which sweep triggeringwill occur and the (+) direction selects the mostpositive point on the sync waveform at which sweeptriggering will occur. The control may be adjusted tostart the sweep on any desired portion of the syncwaveform.
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Fig. 7. Oscilloscope trace with Z-axis input.
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14. The observed waveforms of Channels A and B can beexpanded by a factor of 5 by pulling outward onthe {> POSITION control 8. This control can then berotated clockwise or counterclockwise to view the leftand right extremes of the waveform displays asdesired. Push inward on the control to return thesweep to the normal, non-magnified condition.
15. Calibrated voltage measurements, calibrated time meas-urements and operation with Z-axis input are identicalto those previously described for single-trace operation.Either the Channel A or Channel B vertical adjustmentcontrols can be used as required in conjunction withthe horizontal sweep controls to obtain the requiredamplitude or time interval measurements. This can bedone either by using the dual display facilities such asthe A & B position of the MODE switch or by revertingto single-trace operation, using the CH A or CH Bpositions of the MODE switch.
16. The Channel A and Channel B waveform displays canbe added algebraically by placing the MODE switch inthe A+B position, or subtracted algebraically in theA-B position.
DUAI-TRACE APPLICATIONS
INTRODUCTION
The most obvious and yet the most useful feature of thedual- trace oscilloscope is that it has the capability forviewing simultaneously two waveforms that are frequency-or phase-related, or that have a common synchronizingvoltage, such as in digital circuitry. Simultaneous viewing of"Cause and Effect" waveforms is an invaluable aid to the
U circuit designer or the repairman. Several possible applica-tions of the dual-trace oscilloscope will be reviewed indetail to familiarize the user further in the basic operationof this oscilloscope.
FREQUENCY DIVIDER WAVEFORMS
Fig. 8 illustrates the waveforms involved in a basicdivide-by-two circuit. Fig. A indicates the reference or"clock" pulse train. Fig. B and Fig. C indicate the possibleoutputs of the divide-by-two circuitry. Fig. 8 also indicatesthe settings of specific oscilloscope controls for viewingthese waveforms. In addition to these basic control settings,the TRIGGERING LEVEL control, as well as the ChannelA and Channel B vertical position controls should be set asrequired to produce suitable displays. In the drawing of Fig.8, the waveform levels of 2 cm are indicated. If the exactvoltage amplitudes of the Channel A and Channel Bwaveforms are desired, the Channel A and Channel BVARIABLE controls must be placed in the CAL position.The Channel B waveform may be either that indicated inFig. 88 or 8C. In Fig. 8C the divide-by-two outputwaveform is shown for the case where the output circuitryresponds to a negative-going waveform. In this case, theoutput waveform is shifted with respect to the leading edgeof the reference frequency pulse by a time intervalcorresponding to the pulse width.
DIVIDEBY.8 CIRCUIT WAVEFORMS
Fig. 9 indicates waveform relationships for a basicdivide-by-eight circuit. The basic oscilloscope settings areidentical to those used in Fig. 8. The reference frequency ofFig. 9A is supplied to the Channel A input, and thedivide-by-eight output is applied to the Channel B input.Fig. B indicates the ideal time relationship between theinput pulses and the output pulse.
In an application where the logic circuitry is operating ator near its maximum design frequency, the accumulatedrise time effects of the consecutive stages produce a built-intime propagation delay which can be significant in a criticalcircuit and must be compensated for. Fig. 9C indicates thepossible time delay which may be introduced into afrequency divider circuit. By use of the dual trace oscillo-scope the input and output waveforms can be superimposed
C H A N N E L AWAVEFORM
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C H B
B . D I V I D E - B Y - T W O O U T P U T S Y N C H R O N I Z E D T OL E A D I N G E D G E O F R E F E R E N C E P U L S E
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WAVEFORMB
WAVEFORMA
W A V E F O R M
AH E I G H T
W A V E F O R M
BH E I G H T
Fig. 8. Waveforms in divide-by-two circuit.
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Fig. 9. Waveforrns in divide-by-eight circuit.
to determine the exact amount of propagation delay thatoccurs.
PROPAGATION TIME MEASUREMENTAn example of propagation delay in a divide-by-eight
circuit was given in the previous paragraph. Significantpropagation delay may occur in any circuit with severalconsecutive stages. This oscilloscope has features whichsimplify measurement of propagation delay. Fig. 10 showsthe resultant waveforms when the dual-trace presentation iscombined into a single-trace presentation by selecting theA+B or A-B position of the MODE switch. In the A+Bposition the two inputs are algebraically added in a singletrace display. Similarly, in the A-B position the two inputsare algebraically subtracted. Either position provides aprecise display of the propagation time (Tp). Using theprocedures given for calibrated time measurdment, Tp canbe calculated. A more precise measurement can be obt'ainedif the Tp portion of the waveform is expanded hori-
rf t tr tNct [r loutNcy putst l latN ( l@o R,rsts ptt StcoNo )
zontally. This may be done by pulling the PULL 5X MAGcontrol. It also may be possible to view the desired portionof the waveform at a faster sweep speed.
DIGITAL CIRCI.JIT TIME RELATIONSHIPS
A dual-trace oscilloscope is a necessity in designing,manufacturing and servicing digital equipment. A dual-traceoscilloscope permits easy comparison of time relationshipsbetween two waveforms.
In digital equipment it is common for a large number ofcircuits to be synchronized, or to have a specific timerelationship to each other. Many of the circuits arefrequency dividers as previously described, but waveformsare often time-related in many other combinations. In thedynamic state, some of the waveforms change, dependingupon the input or mode of operation. Fig. 1l shows atypical digital circuit and identifies several of the points atwhich waveform measurements are appropriate. Theaccompanying Fig. 12 shows the normal waveforms to beexpected at each of these points and their timing relation-ships. The individual waveforms have limited value unlesstheir timing relationship to one or more of the otherwaveforms is known to be correct. The dual-trace oscillo-scope allows this comparison to be made. In typicalfashion, waveform No. 3 would be displayed on Channel Aand waveform No. 4 thru No. 8, and No. 10, would besuccessively displayed on Channel B, although other timingcomparisons may be desired. Waveforms No. I I throughNo. 13 would probably be displayed on Channel B inrelationship to waveform No. 8 or No. 4 on Channel A.
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Fig. 10. Using A+B or A-B modes for propagation time measurement.
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In the family of time-related waveforms shown in Fig.12, waveform No. 8 or No. l0 is an excellent sync sourcefor viewing all of the waveforms; there is but one triggeringpulse per frame. For convenience, external sync usingwaveform No.8 or No. l0 as the sync source may bedesirable. With external sync, any of the waveforms may bedisplayed without readjustment of the sync controls.Waveforms No. 4 thru No. 7 should not be used as the svnc
source because they do not contain a triggering pulse at thestart of the frame. It would not be necessary to view theentire waveforms as shown in Fig. 12 in all cases. In fact,there are many times when a closer examination of aportion of the waveforms would be appropriate. In suchcases, it is recommended that the sync remain unchangedwhile the sweep speed or 5X magnification be used toexpand the waveform display.
v C O O E DF U I ICT IO N
0 a r AI I I P U T
( E - 8 t r S )
S E C U R I T Y
8 l r I
S E C U R I T Y
B I T 2
u a 2M U L T I -
P L E X E R
S E C U R I T Y
B I T 3
4 5 6 7 8O A T A E N A E L E
r i D A T A S E L E C T L I N E - O ( 8 )
l 0 u r 3 A
E N D F R A M E R E S E T y + _ - / l l
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Fig. 11. Typical digital circuit using several time-related waveforms.
I 7
DISTORTION MEASUREMENT
Aq qmplifier stage, or an entire amplifier unit, may betested for distortion with this oscillostope. This typ-e ofmeasurement is especially valuable when the slope of awaveform must be faithfully reproduced by an amplifier.Fig. 13 shows the testing of such a circuit using a triangularwave, such as is typically encountered in the recoveredaudio output of a limiting circuit which precedes themodulator of a transmitter. The measurement mav be madeusing any type of signal; merely use the type ofsignal fortesting- that is normally applied to the amplifier- duringnormal operation. The procedure for distortion testingfollows:
l. Apply the type of signal normally encountered in theamplifier under test.
2. Connect Channel A probe to the input of the amplifierand Channel B probe to the output of the amplifier. Itis preferable if the two signals are not inverted inrelationship to each other, but inverted signals can beused.
3. Set CH A and CH B DC-GND-AC switches to AC.
4. Set MODE switch to A & B.
5. Set sync SLOPE switch to CH A and adjust controls asdescribed in waveform viewing procedure, for syn-chronized waveforms.
6. Adjust the CH A and CH B POSITION controls tosuperimpose the waveforms directly over each other.
Z. 44iqrt llle CH A and CH B vertical sensitivity controls(VOLTS/CM and VARIABLE) so that the waveformsare as large as possible without exceeding the limits ofthe scale, and so that both waveforms are exactlv thesame height.
8. Now set the MODE switch to the A-B position (if onewaveform is inverted in relationship to the other, use!!9_A1B position). Adjust the fine vertical sensitivity(CH B VARIABLE) slightly for the minimum re-maining waveform. Any waveform that remains equalsdistortion, if the two waveforms are exactly the sameamplitude and there is no distortion, the waveformswill cancel and there will be only a straight horizontalline remaining on the screen.
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DATA SELECT 'O'----
D A T A C N A B L E
9 RUN
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1 1 M U L T T P L E X E ROUTPUT
L 2LltrtEORIVER OUTPUT
l 3I L- ADORESS _______.,1 FUNCTTON ______! I
I I o a T A ( s a r T s ) | | o A T A ( 8 B t T s ) | |r r l t l l
I D A T A 8 I T I D A T A A I T 2 D A T A B I T 3 II D A T A B I T I D A T A B I T 2 D A T A B I T 3 IM E S S A G E F R A M E - + _ - _ _ _ _ _ J LCNG BLANK PULSE ____=_____l
IO N E C O M P L E T €
IRANSMISSION FRAME
A N Y I N D I V I D U A L A D D R E S S O R F U N C T I O ND A T A B I T M A Y B E P O S I T I V E O R N E G A T I V ED E P E N D I N G U P O N T H E C O D E D I N P U T
l 8
Fig. 12. Family of time-related waveforms from typical digital circuit in Fig. I l.
b
bA-B = D ]STORTION
A D J U S T P O S I T I O NT O S U P E R I M P O S ED I R E C T L Y O V E R
CONTROLSW A V E F O R M SE A C H O T H E R
A C I A & B I A CADJUST SO BOTHWAVEFORMS ARESAME AMPL ITUDE
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vFig. 13. Distortion measurement.
GATED RJNGING CIRCI.JIT
The circuit and waveforms of Fig. 14 are shown todemonstrate the type of circuit in which the dual-traceoscilloscope is effective both in design and troubleshootingapplications. The basic oscilloscope control settings areidentical to those of Fig. 8. Waveform A is the referencewaveform and is applied to Channel A input. All otherwaveforms are sampled at Channel B and compared to thereference waveform of Channel A. The frequency burstsignal can be examined more closely either by increasingthe sweep time per centimeter to .5 mSEC per centimeteror by pulling out on the <> POSITION control to obtain 5times magnification. This control can then be rotated asdesired to center the desired waveform information on theoscilloscope screen.
DELAY LINE TESTS
The dual-trace feature of the oscilloscope can also beused to determine the delay times of transmission typedelay lines as well as ultrasonic type delay lines. The inputpulse can be used to trigger or synchronize the Channel Adisplay and the delay line output can be observed onChannel B. A repetitive type pulse will make it possible tosynchronize the displays. The interval between repetitivepulses should be large compared to the delay time to beinvestigated. In addition to determining delay time, thepulse distortion inherent in the delay line can be determinedby examination of the delayed pulse observbd on theChannel B waveform display. Figure 15 demonstrates thetypical oscilloscope settings as well as the basic test circuit.
Fig. 14. Gated ringing circuit and waveforms.
C H A N N E LA
( I N P U TPU LSE)
C H A N N E LB
( OUTPUTPU LSE) f l @ s @ ?
A&B AC
O U T P U T
5000 PPslpSec PULSE WIDTH
PULSEG E N
U L T R A S O N I CD E L A Y L I N E
( 59 Sec)
Fig. 15. Delay line measurements.
Typical input and output waveforms are shown on theoscilloscope display. Any pulse stretching and ripple can beobserved and evaluated. The results of modifying the inputand output terminations can be observed directly.
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A common application of the delay line checks is foundin color television receivers. Figure 16 shows the oscillo-scope settings and typical circuit connections to check the"Y" delay line employed in the video amplifier section. Theinput waveform and the output waveform are compared fordelay time, using the horizontal sync pulse of thecomposite video signal for reference. The indicated delay isapproximately one microsecond. In addition to determiningthe delay characteristics of the line, the output waveformreveals any distortion that may be introduced from animpedance mismatch or a greatly attenuated output re-mlting from an open line.
STEREO AMPLIFIER SERVICING
Another convenient use for dual-channel oscilloscopes isin troubleshooting stereo amplifiers. If identical channelamplifiers are used and the output of one is weak, distortedor otherwise abnormal, the dual trace oscilloscope can beefficiently used to localize the defective state. With anidentical signal applied to the inputs of both amplifiers, aside-by-side comparison of both units can be made byprogressively sampling identical signal points in bothamplifiers. When the defective or malfunctioning stage hasbeen located, the effects of whatever troubleshooting andrepair methods are employed can be observed and analyzedimmediately.
IMPROVING THE RATIO OFDESIRED TO I.JNDESIRED SIGNALS
In some applications, the desired signal may be riding ona large undesired signal component such as 60 Hz. it ispossible to minimize or for practical purposes eliminate theundesired component. Fig. 17 indicates the oscilloscopecontrol settings for such an application. The waveformdisplay of Channel A indicates the desired signal and thedotted line indicates the average amplitude variation cor-responding to an undesired 60Hz component. The ChannelB display indicates a waveform of.equal amplitude andidentical phase to the average of the Channel I waveform.With the MODE switch set to A-8, and by adjusting the CHB vertical attenuator controls, the 60 Hz component of theChannel A signal can be cancelled by the Channel B inputand the desired waveform can be observed without the 60Hz component.
AMPLIFIER PHASE SHIFT MEASUREMENTSIn the single-trace application section of this manual
phase shift measurements using a single trace are described.In addition, in the square wave testing section, square wavedistortion is explained in terms of phase shift of the signalcomponents which comprise the square wave. These phaseshifts can be verified directly by providing a sine wave inputsignal to the amplifier and observing the phase of theoutput signal with respect to the input signal.
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V I D E OA M P L I F I E R
T O H O R I Z O N T A L A M P L I F I E R .
N O T E : N O E L E C T R I C A L C O N -N E C T I O N ; P L A C E C L I P O NI N S U L A T I O N O F P L A T E C A PL E A D O R I N C L O S E P R O X .I M I T Y O F H O R I Z O N T A L A M P -L I F I E R T U B E .
TO V I DEOOUTPUT
A M P L I F I E R
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. 2V lcm*C A L
S E T B O T H P R O B E S F O R1 O : 1 A T T E N U A T I O N
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TO HORIZONTAL
O E L A Y L I N E
20
Fig. 16. Checking "Y" delay line in color television receivers.
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C H A N N E L A ADJUST FOR ONECOMPLETE CYCLE
AT 60HzC H A N N E L B
lmS/cm
AUTO
SLOPE+
C H A
S I G N A L+60 Hz
60 HzSTART WITH
A & BC H A N G E T O
A _ B
Fig 17. Improving desired-to-undesired signal ratio.
In all amplifiers, a phase shift is always associated with achange in amplitude response. For example, at the -3 dBresponse points, a phase shift of 45" occurs. Fig. l8illustrates a method of determining amplifier phase shift
a.-_ directly. In this particular case, the measurements are being= made it approximately 5000 i{2. The input signal to the
audio amplifier is used as a reference and is applied to theCH A INPUT jack.
The VARIABLE control is adjusted as required toprovide a complete cycle of the input waveform displayed
on 8 cm horizontally. A waveform height of 2 cm is used.The 8 cm display represents 3600 at the flisplayedfrequency and each centimeter represents 45o of thewaveform. The signal developed across the output of theaudio amplifier is applied to the Channel B INPUT jack.The vertical attenuator controls of Channel B are adjustedas required to produce a peak-to-peak waveform of 2 cm asshown in Fig. l88.
The CH B POSITION control is\hen adjusted so that theChannel B waveform is displayed on the same horizontalaxis as the Channel A waveform as shown in Fig. 18B. Thedistance between corresponding points on the horizontalaxis for the two waveforms then represents the phase shiftbetween the two waveforms. In this case, the zero crossoverpoints of the two waveforms are compared. It is shown thata difference of I centimeter exists. This is then interpretedas a phase shift of 45o.
VIDEO EQUIPMENT SERVICING
Many of the video servicing procedures can beperformed using single-trace operation. These are outlinedlater in the applications section covering single-trace opera-tion. One of these procedures, viewing the VITS (verticalinterval test signal), can be accomplished much moreeffectively using a dual-trace oscilloscope. As outlined inthe single-trace applications section and as shown in Fig. 25and 26, the information on the Field #1 and Field #2vertical blanking interval pulse is different. This is shown indetail in Fig. 25. Also, because the oscilloscope sweep issynchronized to the vertical blanking interval waveform,the Field #l and Field #2 waveforms are superimposedonto each other as shown in Fig. 27A. With dual-traceoperation, the signal information on each blanking pulsecan be viewed separately without overlapping. Fig. 19indicates the oscilloscope control setting for viewing thealternate VITS.
l. The video equipment from which the VITS informa-tion is to be viewed must be set to a station trans-mitting a color broadcast.
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lN 8cm
20pS/cm
C H A N N E L
A
C H A N N E L
B
-l l+-45o
C H A N N E L A
C H A N N E L B
OUTPUTLOAD
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Fig. 18. Measuring amplifier phase shift.
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The control settings of Fig. 19 are those required toobtain a 2-field vertical display on Channel A.
With the oscilloscope and television receiver operating,connect the Channel A probe (set at l0: 1) to the videodetector test point.
Set the SYNC switch as follows:
A. If the sync and blanking pulses of the observedvideo signal are positive; use the VIDEO+ switchposition.
B. If the sync and blanking pulses are negative, usethe VIDEO- switch position.
Adjust the sweep time VARIABLE control so that 2vertical fields are displayed on the oscilloscope screen.
Connect the Channel B probe (set to l0:1) to the videodetector test point.
Set the MODE switch to the A & B position. Identicalwaveform displays should now be obtained onChannels A and B.
Place the sweep time VARIABLE control in the CALposition.
Set the SWEEP TIME/CM control to the .lmS/CMposition. This expands the display by increasing thesweep speed. The VITS information will appear towardthe right hand portion of the expanded waveformdisplays. The waveform information on each trace mayappear as shown in the drawing of Fig. 26. Becausethsre is no provision for synchronizing the oscilloscope
display to either of the two fields which comprise acomplete vertical frame, it cannot be predicted whichfield display will appear on the Channel A or ChannelB display.
10. Pull the {} POS control outward to obtain an addi-tional 5X magnification. Rotate the control in acounterclockwise direction moving the traces to theleft until the expanded VITS information appears asshown in Fig.20.
NOTEBecause of the low repetition rate and the highsweep speed combination, the brightness level ofthe signal displays will be reduced.
11. Once the Channel A and Channel B displays have beenidentified as being either Field #l or Field #2 VITSinformation, the probe corresponding to the waveformdisplay which is to be used for signal-tracing andtroubleshooting can be used, and the remaining probeshould be left at the video detector test point to insurethat the sync signal is not interrupted. If the syncsignal is interrupted, the waveform displays mayreverse because, as previously explained, there is noprovision in the oscilloscope to identify either of thetwo vertical fields which comprise a complete frame.
Fig.20 shows the dual-trace presentation of the Field #land Field *2 VITS information. The Field #l informationis disolaved on the bottom trace.
5 .
6.
7.
8.
9.
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22
Fig. 19. Set-up for viewing fields I and 2 of VITS information.
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Fig. 20. Oscilloscope presentation of fields 1 and 2of VITS information.
SINGLE.TRACE APPLICATIONS
INTRODUCTION
ln addition to the dual-trace applications previouslyoutlined, there are, of course, many service and laboratoryapplications where only single-trace operation of theoscilloscope is required. After gaining experience with theoscilloscope, the user will be able to make the judgment asto whether a job cdn be performed more efficiently byusing the single-trace or the dual-trace method of operation.The following are applications in which single-trace opera-tion is adequate. In several cases, it will be found that analternate method using the dual-trace application has beendescribed for the same application. For all the followingapplications the most flexible operation will be achieved ifthe Channel B vertical amplifier is used with the MODEswitch in the CH B position. This arrangement providescomplete triggered sweep as well as free running operationof the oscilloscope, and, in addition, by placing the MODEswitch in the A-B position (with the CH A DC-GND-ACswitch in the GND position), whatever waveform isobtained can be inverted in polarity if desired by theoperator.
VIDEO EQUIPMENT SERVICING
A triggered sweep oscilloscope is advantageous inservicing and aligning television receivers and video taperecorders. This oscilloscope also includes several featuresthat were incorporated to make video servicing easier andmore comprehensive. These features include:
o SWEEP TIME/CM control automatically selectsvertical sync at sweep speeds appropriate for viewingframes and horizontal sync at sweep speeds ap-propriate for viedlng lines.
o Vector overlay for color demodulator checks.
r Wide bandwidth for high resolution video and pulsepresentation.
SIGNALTRACING AND PEAK-TO.PEAKVOLTAGE READINGS
For general troubleshooting and isolation of troubles intelevision receivers (or almost any other electionic equip-ment for that matter), the oscilloscope is an indispensableinstrument. It provides a visual display of absence or
presence of normal signals. This method (signal-tracing)may be used to trace a signal by measuring several points inthe signal path. As measurements proceed along the signalpath, a point may be found where the signal disappears.When this happens, the source of trouble has been located.
However, the oscilloscope shows much more than themere presence or absence of signal. It provides a peak-to-peak voltage measurement of the signal. The cause of poorperformance can often be located by making such peak-to-peak voltage measurements. The schematic diagram oraccompanying service data on the equipment being servicedusually includes waveform pictures. These waveformpictures include the required sweep time and the normalpeak-to-peak voltage. Compare the peak-to-peak voltagereadings on the oscilloscope with those shown on thewaveform pictures. Any abnormal readings should befollowed by additional readings in the suspected circuitsuntil the trouble is isolated to as small an area as possible.The procedures for making peak-to-peak voltage measure-ments are given earlier in the CALIBRATED VOLTAGEMEASUREMENT paragraph.
COMPOSITE VIDEO WAVEFORM ANALYS$
Probably the most important waveform in videoservicing is the composite waveform consisting of the videosignal, the blanking pedestals and the sync pulses. Fig. 2land 22 show typical oscilloscope traces when observingcomposite video signals synchronized with horizontal syncpulses and vertical blanking pulses. Composite video signalscan be observed at various stages of the television receiverto determine whether circuits are performing normally.Knowledge of waveform makeup, the appearance of anormal waveform, and the causes of various abnormalwaveforms help the technician locate and correct manyproblems. The technician should study such waveforms in atelevision receiver known to be in good operating con-dition, noting the waveform at various points in the videoamplifier.
To set up the oscilloscope for viewing television com-posite video waveforms, use the following procedure:
1. Tune the television set to a local channel.
2. Set the MODE switch to the CH B position.
3. Set the SWEEP TIME/CM switch to the l0 pS/cmposition for observing VIDEO+ horizontal lines or tothe 2 mS/cm position for observing VIDEO+ verticalframes.
4. Set the SyNC switch to the VIDEO+ position.
5. Set the SOURCE switch to the CH B position.
6. Pull the TRIGGERING LEVEL control for automaticsync.
7. Set the CH B DC-GND-AC switch to the AC position.
8. Connect a probe cable to the CH B INPUT jack.Connect the ground clip of the probe to the televisionset chassis. With the probe set for l0:l attenuation,connect the tip of the probe to the video detectoroutput of the television set.
9. Set the CH B VOLTS/CM switch for the largest verticaldeflection possible without going off-scale.
10. tf necessary, rotate the TRIGGERING LEVEL controlto a position that provides a synchronized display.
11. Adjust the sweep time VARIABLE control for twohorizontal lines or two vertical frames of compositevideo display.
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TELEVIS ION SET
Fig. 21. Set-up for viewinghoizontal fields of composite video signal.
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24
Fig.22. Set-up for viewingvertical fields of composite video signal.
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12. lf the sync and blanking pulses of the displayed videosignals are positive, set the SYNC switch to ihe VIDEO+position; if the sync and blanking pulses are negative,use the VIDEO- position.
13. Push in the TRIGGERING LEVEL control and rotateto a position that provides a wellsynchronized display.
14. Adjust the INTENSITY and FOCUS controls for thedesired brightness and best focus.
15. To view a specific portion of the waveform, such as thecolor burst, pull outward on the <> POSITION controlfor 5X magnification. Rotate the same control left orright to select the desired portion of the waveform tobe viewed.
16. Composite video waveforms may be checked at otherpoints on the video circuits by moving the probe tip tothose points and changing the VOLTS/CM conirolse-tting as required to keep the display within the limitsgl tlr scale, and by readjusting ttre TRIGGERINGLEVEL control to maintain stabilization. The polarityof the observed waveform may be reversed whenmoving from one monitoring point to another; there-lgt_r, -lt may be necessary to reverse the polarity of theSYNC.
SYNC PUISE ANALYSIS
The IF amplifier response of a television receiver can beevaluated to some extent by careful observation of thehorizontal sync pulse waveform. The appearance of thesync pulse- waveform is affected by ilie IF amplifierbandpass characteristics. Some typical waveform symptomsand their relation to IF amplifier-response are indicaled inFig.. .23. Sync pulse waveform disfortions produced bypositive or negative limiting in IF overload conditions areslrown inFig.24.
Fig.24. Sync pulse waveforms.
The VITS is transmitted during the vertical blankinginterval. On the television set, it can be seen as a brighiwhite line above the top of the picture, when the vertiiallinearity.or height is adjusted to view the vertical blankinginterval (on TV sets with internal retrace blanking circuits,the blanking circuit must be disabled to see the VITS).
The transmitted VITS is a precision sequence of specificfrequency, amplitude, and waveshape as ihown in Fig. 25and 26. The television networks use the precision signals foradjustment and checking of network transmission equip-ment, but the technician can use them to evaluate televisionset performance. The first frame of the VITS (line 17)begins with a "flag" of white video, followed by sine wavefrequencies of 0.5 MHz, 1.5 MHz, 2MHz,3 MHt,3.6 MHz,
II
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l.loRtzofYrALPULSE
OISTORTION
O/ERALL RECEIVERFRECIUENCY RESPONSE
EFFECT ONPICTURE
Normal Circurt
.1Picture Normal
Loss of high frequffiyresponse
\
Loss of picture delarl
Excessrve hrgh frequencyresponse, rcn-lrnearphase shif t I A-
Frne vert ical black andwhite stnatrons fol lwtrna. sharp change rn prcture-snao I ng
Loss of low frequencyrespons€ n
Change in shadrng of larg€prclure areas; smearedOrcture
Fig. 23. Analysis of sync pulse distortion.
Fig. 25. VITS signal, fields I and 2.
vrTs (VERTTCAL TNTERVAL TEST STGNAL)
Most network television signals contain a built-in testsignal (the VITS) that can be a very valuable tool introubleshooting and servicing television sets. This VITS canlocalize trouble to the antenna, tuner, IF or vidpo sectionsand shows when realignment may be required. The follow-ing procedures show how to analyze and interpret oscillo-scope displays of the VITS.
25
NORMALSYNC PULSE
SYNC PULSECOMPRESSION
CAUSED BYLIM ITING
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SATURATIONCAUSED BY
LIMITING
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E Q U A L I Z I N GPUL SE S
NOTEThe brightness level of the signal display will bereduced because, although the repetition rate isonly 60 Hz (a 16,000 pSEC period) the writ ingspeed is 20 pSEC/cm (.1 mSEC/cm magnified fivetimes).
8. The waveform should be similar to that shown in Fig.27. For the oscilloscope display, each vertical syncpulse starts a new sweep. This causes line 17 and line279 (multi-burst) to be superimposed, as are lines l8and 280. The multi-burst signals are identical, whichreinforces the trace. However,l ines l8 and 280 are notidentical and both signals are superimposed over eachother.
F ig .27 . Osc i l loscope presenta t ion o f V ITSinformatio n, single- trac e opention.
9. The presentation of the preceding paragraphs (Fig. 27)is the limit of observation possible with a single-traceoscilloscopy. With the Model 1472C oscilloscope,however, a single-field VITS presentation can beobtained by placing the MODE switch in the A & Bposition. This causes the Channel B information to bedisplayed on alternate sweeps, as are the Field #l andField #2 VITS. Because there is no provision forpreselecting the Field #1 or Field #2information, eitherField #l or Field #2 (Fig. 22) will appear. Themulti-burst information in the VITS is the mostvaluable for troubleshooting television receivers and,because it is present on both Field #1 and Field #VITS, either can be used for troubleshooting and signaltracing.
Now to analyze the waveform. All frequencies of themulti-burst are transmitted at the same level, but shouldnot be equally coupled through the receiver due to itsresponse curve. Fig. 28 shows the desired response for agood color television receiver, identifying each frequency ofthe multi-burst and showing the allowable amount ofattenuation for each. Remember that -6 dB equals half thereference voltage (the 2.0 MHz modulation should be usedfor reference).
To localize trouble, start by observing the VITS at thevideo detector. This wil l localize trouble to a point eitherbefore or after the detector. If the multi-burst is normal atthe detector. check the VITS on other channels. If somechannels look okay but others do not, you probably havetuner or antenna-svstem troubles. Don't overlook the
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Fig. 26. Vertical blanking interval, showing VITSinformation.
(3;8- MHz) and 4.2 MHz. This sequence of frequencies iscalled the "multi-burst". The first lrame of Field #2 (line279) also contains an identical multi-'burst. This multiburstportion of the VITS is the portion that can be mostvaluable to the technician. The second frame of the VITS(line; l8 and 280), which contains the sine-squared pulse,window pulse and the staircase of 3.58 MHz bursts atprogressively lighter shading, are valuable to the network,but have less value to the technician. As seen on thetelevision screen, Field #l is interlaced with Field #2 sothat line 17 is followed by line 279 and line 18 is followedby line 280. The entire VITS appears at the bottom of thevertical blanking pulse and just before the first line ofvideo.
Each of the multi-burst frequencies is transmitted atequal strength. By observing the comparative strengths ofthgse frequencies after the signal is processed through thetelevision receiver, the 'frequency response of the set ischecked.
Set up the oscilloscope as follows to view the VITS:
l . Connect the CH B probe (set at 10: l ) to the output ofthe video detector or other desired test point in thevideo section of the television set.
2. If the television set has a vertical retrace blankingcircuit, bypass this circuit during the measurement.
3. Set the MODE switch to cH B.
4. Set up the oscilloscope for TV vertical composite videowaveform analysis as previously described. Two verticalframes will be visible.
5. Place the sweep time VARIABLE control in the CALposition.
6. Reduce sweep t ime to. l mi l l isecondper cent imeter ( .1ms/CM) with the SWEEP TIME/CM switch. This91pa1ds the display by increasing the sweep speed. TheVITS information will appear to the righl on theexpanded waveform display.
7. Further expand the sweep with the 5X magnification(pull outward on the <) POSITION control). Rotatethe <> POSITION control in a counterclockwise direc-!igl, moving the trace to the left, until the expandedVITS appears.
26
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MODUTATION
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60
70
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Fig. 28. Color TV IF amplifier response curve.
chance of the antenna system causing "holes" or tiltedresponse on some channels. If the VITS is abnormal at thevideo detector on all channels, the trouble is probably inthe IF amplifier stages.
As another example, let us assume that we have a set onthe bench with a very poor picture. Our oscilloscope showsthe VITS at the video detector to be about normal exceptthat the burst at 2.0 MHz is low compared to the bursts oneither side. This suggests an IF trap is detuned into thepassband, chopping out frequencies about 2 MHz belowthe picture carrier frequency. Switch to'another channelcarrying VITS. If the same thing is seen, then our reasoningis right, and the IF amplifier requires realignment. If thepoor response at 2 MHz is not seen on other channels,maybe an FM trap at the tuner input is misadjusted, causinga bite on only one channel. Other traps at the input of theset could similarly be misadjusted or faulty.
If the VITS response at the detector output is normalfor all channels. the trouble will be in the video amplifier.look for open peaking coils, off-value resistors,
-solder
bridges across foil patterns, etc.
VECTORSCOPE OPERATION
Performance testing and adjustment of the color circuitsin color television receivers is simplified by using thevectorscope operation of the oscilloscope. The additionalequipment needed is a color bar generator. TheB & K-Precision color bar generators are ideally suited forthis.
First the horizontal and vertical gain of the oscilloscopemust be equalized (see Fig. 30).
l. Attach vector overlay to scope. Pull off bezel, insertoverlay, re-attach bezel. (Refer to MAINTENANCE
ly AND C,lrtgRATION section for graticule iemoval.)
2. Connect the color bar generator to the television setand tune in the color bar pattern.
m+o
G R A T I C U L E
V E C T O RO V E R L A Y
Fig.29. Installation of vector overlay.
Adjust the television set's hue and brilliance controls tomid-range.
Set SWEEP TIME/CM control to the CH B position.
Connect probe cables to the CH A and CH B INPUTjacks. Channel A is the vertical input and Channel B isthe horizontal input. Connect both probe tips to thedriven element of the red gun, usually the grid. If thecathode is the driven element, then connect to thecathode. (The driven element is the element to whichthe output signal of the color amplifier is applied.)
Adjust the CH A (vertical gain) and CH B (horizontalgain) VOLTS/CM and VARIABLE controls to obtain aiompressed 45o pattern that approximately fills thevector overlay. The oscilloscope is now set up forvectorscope operation.
For vector presentation, merely move the horizontalprobe to the driven element of the blue gun. The colorvector pattern is the same type as given by thetelevision set manufacturer. Fig 31 shows typicaldisplays obtained for sets using 105o systems and 90"systems with either grid drive or cathode drive.
NOTE
If the picture tube uses cathode drive, the burstwill appear on the right side of the screen. Justrotate the vector overlay 180o so the BURST labelis on the right side. The color bars will then alignwith the vector overlay.
The vector display provides a very quickmeasurement of the functions of the demodulatorsin a color TV set. The serviceman should famil-iaize himself with the effect on the patternproduced by the color controls. He should observethat the color amplitude control will vary the sizeof the petals but not their position. The huecontrol changes the position of the petals but nottheir amplitude. Lastly, l05o sets wil l have a moreell iptical pattern than 90o sets. The table belowlists some common troubles and their effect on thepattern.
The vector display can be used to check therange of the color set's hue control. It should bepossible to rotate the R-Y petal about the verticalaxis. At the center of the hue control the R-Ypetal should be vertical. tf it is not, locate theCHROMA reference oscillator. In most sets thisoscillator is transformer-coupled to the demodula-tors.
A slight touch-up of this transformer is all thatis necessary to bring the R-Y petal to a verticalposition. Do not attempt to make any adjust-ments on the chroma bandpass amplifiers. This
-b
3 .
4.
5
6 .
7 .
27
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Fig. 30. Equalizing horizontal and vertical gain for Vectorscope operation.
amplifier is aligned by a sweep generator andc-annot in general be aligned by just a vectordisplay.
If the set has adjusted demodulators, the vectordisplay_can also be used for demodulator align-ment. Follow the manufacturer's alignment pio-cedure to locate the proper coils and instead ofcounting_bars simply adjust for the correct anglebetween R-Y and B-Y.
NOTES
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Fig. 31. Vectorscope operation and patterns.
NOTES
G R I DD R I V E
R.Y
CATHODED R I V E
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G R I D C A T H O D ED R I V E D R I V E
1 050
VECTOR D ISPLAYS FOR 105 'P ICTURE TUBE
TROUBL E
Loss of color syncOver loading of co lor ampl i f ie rsColor ampl i f ie rs unbalanced or
weakLack of range of hue control
Demodulator out o f a l ignment
EFFECT ON PATTERN
Peta ls o f pat tern wi l l ro ta tePetals are crushed or f lattenedFlower pat tern very e l l ip t ica l
R-Y petal cannot be made to bever t ica l
Angle between R-Y peta l and B-Ypetal not to manufacturer 'sspec i f ica t ion (90" or 105"Genera l Spec i f ica t ion) .
R E D
EFFECT ON T .V . P ICTURE
Vary ing co lorsColor d is tor t ionColor d is tor t ion
Hue cont ro l won ' t ad justf leshtones
Wrong co lors
B-Y-r-
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29
TELEVISION ALIGNMENT
INTRODUCTION
Alignment of tuners, the video IF strip, and chromacircuits in television receivers requires a high qualityoscilloscope, such as this instrument. The additional piecesof test equipment required are sweep generators for videosweep, IF sweep and RF sweep, marker generators, DC biassupplies and a VTVM. The sweep generator method ,ofalignment displays a bandpass response curye on the screenof the oscilloscope of the type always shown in theorybooks and in the television set manufacturer's alignmentinstructions (typical response curves are shown in Fig. 32).
6 7
4 6
66
4 7
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6 5
4 8
6 U H Z W r 0 €
5 8 v H Z
( 7 5 H H Z )
CHROUA TAXE-OFFCOIL RESPONSE
OVERALL C}RorIARESPOTS€
Fig. 32. TV response curves obtained by sweep-frequency technique.
The ideal instruments for television alignment are thisoscilloscope and the B & K-Precision Sweep/MarkerGenerator. The B & K-Precision Sweep/Marker Generatorprovides all necessary sweep ranges, markers and DC biasvoltages, all from one instrument. The simplified operatingprocedure and calibrated accuracy of the instrument resultsin precision alignment.
For complete alignment instructions of each particulartelevision set, follow the manufacturer's instructions. How-ever, the following general set-up instructions demonstratesuse of the oscilloscope for sweep-frequency alignment.
In this manual, only the proper use of the oscilloscope intelevision is emphasized. Proper use of the sweep generatorand other equipment required for alignment should beprovided in the instruction manuals for those instruments.
3 0
NOTEFor a comprehensive analysis of television align-ment, we recommend the instruction manual forthe B & K Model 415 Sweep/Marker Generator.This "handbook of television alignment" includesnot only the procedures for using the instrument,but all the how and why answers about televisionalignment in general. Even if you use other sweepgenerators, this comprehensive manual providesvaluable procedures, insights and tips that willmake alignment easier and more professional. Themany. illustrations and easy-to-understand step-by-step approach qualify it as the "how to align"textbook. Copies are available from yourB & K-Precision distributor or the factory.
IMPORTANCE OF SWEEP ALIGNMENT
The most rapid way to determine the overall conditionof the tuner, IF and chroma portions of the televisionreceiver is to provide a constant-amplitude signal whichsweeps through the entire bandwidth of a given televisionchannel at a controlled, repetitive rate. As this signal isprocessed through the tuned portions of the receiver, it isshaped by the gain and bandpass properties of the varioussections. Because the signal is channeled from one series oftuned circuits to another it is important that each sectionhas the proper characteristics. If the signal is demodulatedat certain points and the envelope observed, the gain andbandwidth properties up to that point can be determined.
Fig. 32 shows the sweep signal with basic responsecurves of the tuner, IF amplifiers and chroma bandpasscircuits below it. The bandwidths shown are approximatelyto scale. These outlines are similar to the curvei that woulilbe obtained if the outputs of the various sections of the TVreceiver were demodulated and the curve observed on anoscilloscope. Because of the relative bandwidths, the tunerresponse is least critical.
Some reference frequencies are identified to show theimportance of proper alignment. Notice that the chromafrequencies are on the slope of the IF response curve. Thisarea is the most critical because improper IF alignment inthis area will affect the amplitude and shape of the chromaresponse curve and this in turn affects color picture quality.
Notice that the chroma information is located on aconstant-amplitude portion of the transmitted televisionspectrum. Notice that the relative amplitudes of the chromainformation are modified by passing through the tunedcircuits of the television receiver tuner and IF amplifiers.This is shown by reference to the overall IF response curve.Notice that the signal information at the uppei end of thechroma frequency range (4.08 MHz) is reduced inamplitude with respect to the signal level at the lower endof the chroma frequency range (3.08 MHz). To compensatefor this frequency-versus-amplitude characteristic
-of the
overall IF response curve, a chroma takeoff coil is usedbetween the IF output and the bandpass amplifier of thechroma portion of the receiver. The chroma takeoff coil istuned to the upper end of the chroma frequency range,!!ua!!y 4.08 MHz and provides a response as shown in Fig.32. This compe,nsates for the amplitude-versus-frequencycharacteristic of the chroma portion of the oveiall IFresponse curve. The result of combining the response of theIF curve and the response of the chroma takeoff coil is toproduce g qql_ overall response in the chroma frequencyrange (3.08 MHz to 4.08 MHz). The resultant signal is their
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\
\-
applied to the bandpass amplifier which has the responseindicated by the overall chroma response cuive.
Alignment of the chroma takeoff coil is sometimesspe-cified as a separate step in manufacturer's test pro-cedures. In other procedures, adjustment of the chromatakeoff coil is performed together with the adjustment ofthe bandpass transformer.
SWEEP ALIGNMENT METHODSThe best method of checking alignment and determining
which stages require alignment is to inject an RF sweepfrequency signal at the tuner antenna teiminals. The AGCbias line must be clamped by application of bias orgrounding the AGC line. The outputs of the IF and chromacircuits are then observed on an oscilloscope and comparedto the manufacturer's recommended response curye.
The technician can then decide which portions of thereceiver require alignment. For example, if the IF responseis satisfactory but the chroma response is not, then theproblem is between the video detector output of the IFstrip and the output of the bandpass amplifier. If the IFresponse and the chroma response are poor then it is mostlikely that the IF requires touch-up, particularly if theresponse is poor on the slope affecting chroma response.
The RF portion of the tuner seldom creates an align-ment problem because the passband is so much greater thanthat of the IF section; however, the mixer output circuit,which is located on the tuner, may require attention. This ispart of the tuned matching network between the tuner andthe first IF stage. A separate pre-alignment procedure is
given for the link circuits by some manufacturers.
Once the deficient portion of the receiver is determined,an alignment check of that section can be performed. Thealignment procedures vary with manufacturers. Somesuggest signal combinations at the tuner antenna terminalswhich can generate IF and video sweep frequencies in thereceiver so that overall alignment can be done by selectingthe right combination of input signals. One way of doingthis is to first connect an RF sweep generator for IFalignment. After this is complete, the picture carrierfrequency for the channel being used is selected and this ismodulated by a video sweep signal (this is the VSM, orvideo sweep modulation method). This video sweepmodulation is demodulated at the video detector of the TVreceiver and applied to the chroma bandpass circuits for thealignment of these stages.
Other manufacturers recommend an IF sweep frequencyinjected at the mixer grid (or base, if transistorized) for IFalignment. The IF picture carrier frequency (45.75 MHz) isthen modulated with a video sweep voltage (VSM again). Asbefore this is detected at the video detector of the TVreceiver and the recovered sweep voltage is used for thechroma circuit alignment.
Another method is to first video-sweep align the chromacircuits directly. The IF is then aligned and video sweepmodulation of the IF pix frequency (45.75 MHz) is used tocheck the combined effect on the chroma response of IFalignment and chroma alignment. Usually a touch-up of thechroma circuits is necessary to obtain the desired finaloverall chroma response.
U^tE--l
0C H B
A N T E N N AT E R M I N A L S
C H A N N E LS E L E C T O R
c t 6 2u/1e'
c , ) ( l r o'V.5a r a ' T E L E V I S I O N S E T .
@ [ r - l
@
z L=Jg
. 0 1 V / c m A D J U S TH O R I Z O N T A L
S I Z E
S W E E P / M A R K E RG E N E R A T O R
R F S W E E PO U T V O L T A G E
Fig. 33. Typical tuner alignment set-up.
5
3 1
In conjunction with If alignment, practically all manu-facturers recommend pre-tuning IF traps by inj-ecting spotfrequencrls into the IF (usually at a specified tuner testpoint). Other procedures outline a prealignment of alltuned circuits in the IF before sweep alignment procedures.
In all cases the manufacturer's method is the best for hisparticular receiver and the manufacturer's service manual ispreferred for alignment. SAMS PHOTOFACT proceduresare also reliable and in most cases repeat the manufacturer'sprocedure. If complete realignment of an apparentlydeficient receiver does not restore the required risponse,the technician must then consider that a component iailurehas occurred and must employ standard trbubleshootingprocedures.
TLJNER ALIGNMENT (Refer to Fig. 33)
1. Connect the output of the sweep generator to theantenna terminals of the television set. Adiust thesweep generator to sweep one of the TV chann6ls.
2. Tune the TV set to the same channel.
3. Connect the ground clip of the oscilloscope probedjrectly to- the tuner shield to minimize hum piikup.Connect the Channel A (Vertical) probe (set ioDIRECT) to the tuner test point. The tuner tesi pointis-normally th9 grid of the mixer tube or equivalent,where a demodulated signal is present.
4. Set the vertical controls (CH A VOLTS/CM andVARIABLE) for maxirhum sensitivity and operate the
sweep generator at low level to avoid overloading thetelevision receiver, which would distort the responsecurve and provide an erroneous picture of alignment onthe oscilloscope screen.
5. The oscilloscope sweep and sweep generator must be inexact synchronization and phase with each other forproper presentation. of the response curve. This is easilyaccomplished for sinusoidal or sawtooth sweep byqgtlllg the oscilloscope for external horizontal input(SWEEP TIME/CM to CH B.position) and connectlngthe horizontal sweep voltage from the sweep generatorto the Channel B input terminal on the oscilloscope.
6. Select the marker generator frequencies required tomeasure the upper and lower response of the tuner.
7. The tuner response curve is now displayed on theoscilloscope. See the manufacturer's instructions forthe response curve specifications and the necessaryadjustments for realignment.
IF ALIGNMENT (Refer to Fig. 34)
l. Connect the output of the sweep generator to thesignal injection point of the mixer. Adjust the sweepgenerator to sweep the IF frequency band. (lf thetuner has been properly aligned, RF sweep may beapplied at the antenna terminals).
2. Synchronize the oscilloscope sweep with the sweepgenerator as previously described in the TTINERALIGNMENT procedure.
@
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Lvr
[ ' - l uElg
C H B
S W E E P / M A R K E RG E N E R A T O R
SWEEPVOLTAGE
@o
.01V/cm ADJUSTHORIZONTAL
s rzE
D I R E C T
- V I D E O
D E T E C T O R
A G CB I A S
Fig. 34. Typical IF alignment set-up.
32
:
4.
5 .
6.
3 .
4.
5 .
6.
7 .
Connect the ground clip of the oscilloscope verticalprobe to the television set chassis.
Connect the vertical probe of the oscilloscope to thevideo detector output.
Set the vertical gain controls (CH A VOLTS/CM andVARIABLE) for suitable viewing of the responsecurve.
Keep the sweep generator output level low to preventoverloading. Follow the manufacturer's recommenda-tions on disabling AGC.
Select the marker generator frequencies required tocheck the critical frequencies of interest (see Fig. 35).A sweep and marker generator capable of displaying allt h e m a r k e r s s i m u l t a n e o u s l y , s u c h a s t h eB & K-Precision Model 415, is a big advantage.
Follow the manufacturer's instructions for evaluatingthe response curve and making the alignment.
Fig. 35. Typical IF response curve, showing toleranceranges of response levels.
CHROMA ALIGNMENT (Refer to Fig. 36)
The IF alignment must be satisfactorily completedbefore starting this chroma alignment procedure. If directinjection of video sweep is used rather than the IF sweepinjection specified herein, the response curye is altereddrastically. Follow the manufacturer's procedure explicitlyfor such direct injection of video sweep for chromaalignment.
1. kave the sweep/marker generator and AGC biasconnected as for IF alignment. Set the sweep generatorto sweep approximately the 4l to 44 MHz band offrequencies. Use the same IF injection level that wasused for IF alignment.
2. Apply the proper DC bias to the color killer to enablethe color amplifiers (bandpass amplifiers). Refer to themanufacturer's instructions for the correct.bias level.
3. Synchronize the oscilloscope sweep as previouslydescribed for tuner alignment.
Use a demodulator probe for the vertical input(Channel A) to the oscilloscope. Measure the responsecurve at the input to the demodulators.
Set the vertical gain controls of the oscilloscope (CH AVOLTS/CM and VARIABLE) for a convenient viewingsize on the screen.
A response curve similar to that shown in Fig. 37should be seen. Select the marker generator frequenciesof interest. Refer to the manufacturer's instructions forbandpass specifications and alignment procedure.
Fig. 37. Typical chroma response curve, showingtolerance ranges of response levels.
NOTES
8.
3 3
42.67MHZ - ,
II
85% * l5olo -
/.. 1 7.25 MHZ47.24
x' MHZ
P t )45.75
3.58 MHZ
3 08 MHz -l 4.O8 MHZ
9t/" tlOo/"-
/ VALLEYI50/o MAX
TILT IOTO MAX
4 . 5 0 M H Z
\t
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@61 @C H B
@ [ ' l '
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R FO U T
S W E E P / M A R K E RG E N E R A T O R
A C
ADJUST ADJUSTVERTICAL HORIZONTAL
S I Z E S I Z E
M I X E R
S W E E PV O L T A G E
A G CB I A S
TELEVIS ]ON SET
D E M O D U L A T O RP R O B E
V I D E . OD E T E C T O R
V I D E OA M P
S E C O N DC O L O R A M P( B A N D P A S S
A M P )
F I R S TC O L O R A M P
C O L O RK I L L E R
3
L
34
Fig. 36. Typical chroma alignment set-up.
Y
1
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I \- 7 t
U
@
0
0@l
[=]
C H B
o@
@
I
S W E E PG E N E R A T O R
M A R K E R R F S W E E PI N P U T O U T V O L T A G E
D I R E C T
r - -I
F M R E C E I V E R
A C I I A C
VERTICAL HORlZONTALs rzE s tzEM A R K E R
G E N E R A T O R
M I X E R D E M O D U L A T O R
Fig. 38. Typical FM receiver alignment set-up.
FM RECEIVER ALIGNMENTRefer to Fig. 38
Procedure:
l. Connect a sweep generator to the mixer input of theFM receiver. Set the sweep generator for a 10.7 MHzcentered sweep.
2. Connect the sweep voltage output of the sweepgenerator to the Channel B input jack of the oscillo-scope and set the oscilloscope controls for externalhorizontal sweep (SWEEP TIME/CM to CH B).
3. Connect the vertical input probe to the demodulatorinput of the FM receiver.
4. Adjust the oscilloscope vertical and horizontal gaincontrols for display similar to that shown in Fig. 38A.
5. Set the marker generator precisely to 10.7 MHz. Themarker "pip" should be in the center of the bandpass.
6. Align the IF amplifiers according to the marlufacturer'sspecifications.
7. Move the probe to the demodulator output. The "S"
curve should be displayed. arid the 10.7 MHz "pip"
should appear exactly in the center (see Fig. 388).Adjust the demodulator according to the manu-facturer's instructions so the marker moves equaldistances from center as the marker frequency isincreased and decreased equal amounts from the 10.7MHz center frequency.
PHASE MEASUREMENT
Phase measurements may be made with an oscilloscope.Typical applications are in circuits designed to produce aspecific phase shift, and measurement of phase shiftdistortion in audio amplifiers or other audio networks.Distortion due to non-linear amplification is also displayedin the oscilloscope waveform.
A sine wave input is applied to the audio circuit beingtested. The same sine wave input is applied to the verticalinput of the oscilloscope, and the output of the testedcircuit is applied to the horizontal input of the oscilloscope.The amount of phase difference between the two signalscan be calculated from the resulting waveform.
To make phase measurements, use the following pro-cedure (Refer to Fig. 39).
3 5
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A U D I OS I G N A L
G E N E R A T O R
(tC H B
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A U D I ONETWORK
B E I N G T E S T E D
!
bFig. 39. Typical phase measurement alignment set-up.
l .
2.
Using an audio signal generator with a pure sinusoidalsignal, apply a sine wave test signal at the desired testfrequency to the audio network being tested.
Set the signal generator output for the normaloperating level of the circuit being tested. If desired,the circuit'sr output may be observed on the oscillo-scope. If the test circuit is overdriven, the sine wavedisplay on the oscilloscope is clipped and the signallevel must be reduced.
Connect the Channel B probe to the output of the testcircuit.
Set the SWEEP TIME/CM control to CH B.
Connect the Channel A INPUT probe to the input ofthe test circuit. (The input and output test connectionsto the vertical and horizontal oscilloscope inputs maybe reversed.)
Adjust the Channel A and B gain controls for a suitableviewing size.
Some typical results are shown in Fig. 40. If the twosignals are in phase, the oscilloscope trace is a straightdiagonal line. If the vertical and horizontal gain areproperly adjusted, this line is at a 45" angle.
A .90" phase shift produces a circular oscilloscopepattern.
Fig.40. Typical phase measurement oscilloscopedisplays.
3 .
4.
5 .
7.
36
N O A M P L I T U O E O I S T O R T I O N
N O P H A S E S H I F T
A M P L I T U D E O I S T O R T I O N
N O P H A S E S H I F T
O U T O F P H A S EN O A M P L I T U D E D I S T O R T I O N
P H A S E S H I F T
A M P L I T U D E O I S T O R T I O NP H A S E S H I F T
9 o O o U T o F P H A S E
v
g
il
B- A
= P H A S E A N G L E
Fig.41. Phase shift calculation.
FREQUENCY MEASUREMENT
Procedure:
l. Connect the sine wave of known frequency to the CHB INPUT jack of the oscilloscope and set the SWEEPTIME/CM control to CH B. This provides externalhorizontal input.
2. Connect the vertical input probe (CH A IMUT) to theunknown frequency.
3. Adjust the Channel A and B size controls for aco4venient, easy-to-read size of display.
4. The resulting pattern, called a Lissajous pattern, showsthe ratio between the two frequencies. See Fig.42.
Phase shift of less (or more) than 90o produces anelliptical oscilloscope pattern. The amount of phase shiftcan be calculated from the oscilloscope trace as shown inF i g . 4 1 .
SQUARE WAVE TESTING OF AMPLIFIERS
INTRODUCTION
A square wave generator and a low-distortion oscillo-scope, such as this instrument, can be used to displayvarious types of distortion present in electronic circuits. Asquare wave of a given frequency contains a large numberof odd harmonics of that frequency. If a 500 Hz squarewale in injected into a circuit, frequency components of1.5 kHz, 2.5 kHz,3.5 kHz, also are provided. Since vacuumtubes and transistors are non-linear, it is difficult to amplifyand reproduce a square wave which is identical to the inputsignal. Interelectrode capacitances, junction capacitances,stray capacitances as well as limited device and transformerresponse are a few of the factors which prevent faithfulreproduction of a square wave signal. A well-designedamplifier can minimize the distortion caused by theselimitations. Poorly designed or defective amplifiers canintroduce distortion to the point where their performanceis unsatisfactory.
UNKN0r . /N FREQUENCYT O V E R T I C A L I N P U T ,STANOARt) FREQUENCYTO HOR IZONTAL INPUT
RAT IO OFUN KNOW N
T OSTANDARD
1 : I
l : l
t \ : I
6 : I
S E E N O T E ( ( E ) )
sEEN.TE /2O$t
N O T E : A N Y O N E O F T H E S E F I G U R E S D E P E N D I N GU P O N P H A S E R E L A T I O N S H I P
Fig.42. Lissajous waveforms used for frequencymeasurement.
As stated before, a square wave contains a large numberof odd harmonics. By injecting a 500 Hz sine wave into anamplifier, we can evaluate amplifier response at 500 Hzonly, but by injecting a square wave of the same frequencywe can determine how the amplifier would respond toinput signals from 500 Hz up to the l5th or 2lst harmonic.
The need for square wave evaluation becomes apparentif we realize that some audio amplifiers will be requiredduring normal use to pass simultaneously a large number ofdifferent frequencies. With a square wave, we have acontrolled signal with which we can evaluate the input andoutput quality of a signal of many frequencies (theharmonics of the square wave) which is what the amplifiersees when amplifying complex waveforms of musicalinstruments or voices.
The square wave output of the signal generator must beextremely flat so that it does not contribute to anydistortion that may be observed when evaluating amplifierresponse. The oscilloscope vertical input should be set toDC as it will introduce the least distortion, especially at lowfrequencies. When checking amplifier response, the fre-quency of the square wave input should be varied from thelow end of the amplifier bandpass up toward the upper endof the bandpass; however, because of the harmonic contentof the square wave, distortion will occur before the upperend of the amplifier bandpass is reached.
It should be noted that the actual response check of anamplifier should be made using a sine wave signal. This tsespecially important in limited bandwidth amplifiers (voiceamplifiers). The square wave signal provides a quick checkof amplifier performance and will give an estimate ofoverall amplifier quality. The square wave also will revealsome deficiencies not readily apparent when using a sinewave signal. Whether a sine wave or square wave is used fortesting the amplifier, it is important that the manufacturer'sspecifications on the amplifier be known in order to make abetter judgment of its performance.
37
TESTING PROCEDURE (Refer to Fig. 43)
1. Connect the output of the square wave generator tothe input of the amplifier being tested.
2. Connect the CH B test probe of the oscilloscope to theoutput of the amplifier being tested.
3. If the DC component of the circuit being tested issufficiently low to allow both the AC and DCcomponent to be viewed, use the DC position of theAC-GND-DC switch. However, the AC position may beused without affecting the results except at very lowfrequencies (below 5 Hz).
4. Adjust the vertical gain controls for a convenientviewing height.
5. Adjust the sweep time controls for one cycle of squarewave display on the screen.
6. For a close-up view of a portion of the square wave,use the 5X magnification.
ANALYZING THE WAVEFORMS
The short rise time which occurs at the beginning of thehalf-cycle is created by the in-phase sum of all the mediumand high frequency sine wave components. The same holdstrue for the rapid drop at the end of the half-cycle from
maximum amplitude to zero amplitude at the 1800 orhalf-cycle point. Therefore, a theoretical reduction inamplitude alone of the high frequency components shouldproduce a rounding of the square corners at all four pointsof one square wave cycle (See Fig. q.
:
1
, iI
IL
Fig.44. Square wave response with high frequencyloss.
v
38
ADJUST SWEEPSPEED FOR 1
CYCLE D ISPLAY
S O U A R E W A V EG E N E R A T O R
C H B
ADJUST VERTGAIN FOR
CONVENI ENTVIEWINGH E I G H T
@
o0
o@
@l-,l o =Lrfla,
OUTPUT
A M P L I F I E RC I R C U I T
B E I N G T E S T E D
Fig. 43. Equipment set-up for square wave testing of amplifiers.
v
Distortion can be classified into three distinct categories:
l. The first is frequency distortion and refers to thechange from normal amplitude of a component of acomplex waveform. [n other words, the introduction inan amplif ier circuit of resonant networks or selectivefi lters created by combination of reactive componentswill create peaks or dips in an otherwise flat frequencyresponse curve.
2. The second is non-linear distortion and refers to achange in waveshape produced by application of thewaveshape to non-linear components or elements suchas vacuum tubes, an iron core transformer, and in anextreme case. a deliberate non-linear circuit such as aclipper network.
3. The third is delay or phase distortion, which isdistortion produced by a shift in phase between one ormore components of a complex waveform.
In actual practice, a reduction in amplitude of a squarewave component (sinusoidal harmonic) is usually caused bya frequency-selective network which includes capacity,inductance or both. The presence of the C or L introduces adifference in phase angle between components, creatingphase distortion or delay distortion. Therefore, in squarewave testing of practical circuitry, we will usually find thatthe distorted square wave includes a combination ofamplitude and phase distortion clues.
In a typical wide band amplifier, a square wave checkaccurately reveals many distortion characteristics of thecircuit. The response of an amplifier is indicated in Fig. 45,revealing poor low-frequency response along with over-compensated high-frequency boost. A 100 Hz square waveapplied to the input of this amplifier will appear as in Fig.464'. This figure indicates satisfactory medium frequencyresponse (approximately 1 kHz to 2 kHz) but shows poorlow frequency response. Next, a 1000 Hz square waveapplied to the input of this same amplifier will appear as inFig. 468. This figure displays good frequency response inthe region of 1000 to 4000 Hz but clearly reveals theovercompensation at the higher 10 kHz region by the sharprise at the top of the leading edge of the square wave.
As a rule of thumb, it can be safely said that a sQuarewave can be used to reveal response and phase relationshipsup to the l5th or 20th odd harmonic or up to approx-imately 40 times the fundamental of the square wave. Usingthis rule of thumb, it is seen that wide-band circuitry willrequire at least a two-frequency check to properly analyzethe complete spectrum. In the case illustrated by Fig. 45, a100 Hz square wave will encompass components up toabout 4000 Hz. To analyze above 4000 Hz and beyond10,000 Hz, a 1000 Hz square wave should be satisfactory.
Now, the region between 100 Hz and 4000 Hz in Fig. 45shows a rise from poor low-frequency response to aflattening out from beyond 1000 and 4000 Hz. Therefore,we can expect that the higher frequency components in the100 Hz square wave will be relatively normal in amplitudeand phase but that the lower frequency components in thissame square wave will be strongly modified by the poorlow-frequency response of this amplifier. See Fig. 46,{.
If the combination of elements in this amplifier weresuch as to only depress the low frequency components inthe square wave, a curve similar to Fig. 47'would beobtained. However, reduction in amplitude to a com-ponent, as already noted, is usually caused by a reactiveelement, causing, in turn, a phase shift of the component,
Fig.45. Response curve of amplifier with poor lowand high ends.
Fig.46. Resultant 100 Hz and I kHz square wavesfrom amplifier in Fig. 45.
Fig47. Reduction of square wave fundamentalfrequency component in a tuned circuit.
ulozoo'31,t||G
I O K H Z
roo Hz
SOUAREWAVE
I KH7
SOUAREWAVE
39
Fx3 d)T trPHAff (IEAD),
Fig. 48. Square wave tilt resulting from 3rd harmonicphase shift.
FXI WT tr PHASE (LEAD)
Fig.49. Tilt resulting from phase shift of funda-mental frequency in a leading direction.
Fxl OUT-OFPUASE
Fig. 50. Tilt resulting from a phase shift of funda-'mental frequency in a lagging direction.
producinf the strong tilt of Fig. 46A. Fig. 48 reveals agraphical development of a similarly tilted square wave. Thetilt is seen to be caused by the strong influence of thephase-shifted 3rd harmonic. It also becomes evident thatvery slight shifts in phase are quickly shown up by tilt inthe square wave.
Fig. 49 indicates the tilt in square wave shape producedby a 10" phase shift of a low frequency element in a leadingdirection; Fig. 50 indicates a 10o phase shift in a lowfrequency component in a lagging direction. The tilts areopposite in the two cases because of the difference inpolarity of the phase angle in the two cases as can bechecked through algebraic addition of components.
Fig. 51 indicates low frequency components which havebeen reduced in amplitude and shifted in phase. It will benoted that these examples of low frequency distortion arecharacterized by change in shape of the flat top portion ofthe square wave.
Fig. 468, previously discussed, revealed high-frequencyovershoot produced by rising amplifier response at thehigher frequencies. It should again be noted that thisovershoot makes itself evident at the top of the leadingedge of the square wave. This characteristic relationship isexplained by remembering that in a normal well-shapedsquare wave, the sharp rise of the leading edge is created bythe summation of a practically infinite number of harmoniccomponents. If an abnormal rise in amplifier responseoccurs at high frequencies, the high frequency componentsin the square wave will be amplified disproportionatelygreater than other components creating a higher algebraicsum along the leading edge.
3
!
Fig. 51. Low frequency component loss and phaseshift.
Fig. 52. Effect of high-frequency boost and poordamping.
40
v
Fig. 52 indicates high frequency boost in an amplifieraccompanied by a lightly damped "shock" transient. Thesinusoidal type of diminishing oscillation along the top ofthe square wave indicates a transient oscillation in arelatively high "Q" network in the amplifier circuit. In thiscase, the sudden transition in the square wave potentialfrom a sharply rising, relatively high frequency voltage, to alevel value of low frequency voltage, supplies the energy foroscillation in the resonant network. If this network in theamplifier is reasonably heavily damped, then a single cycletransient oscillation may be produced as indicated in Fig.53 .
Fig. 54 summarizes the preceding explanations andserves as a handy reference.
Fig. 53. Effect of high-frequency boost and gooddamping.
A. Frequency distortion. (crmplitudereduction of low lrequenry com-ponent). No phose shilt.
B. Low frequency boost (occentu-oted fundcrmentol).
C. High frequency loss-No phaseshilt.
Low freguency phose shilt. E. low lrequency loss ond phoseshiIt .
F. High frequenry loss qnd low lre-qrrency phose shilt.
G. High lrequency loss ond phcseshilt.
H. Domped oscillotlon Low frequency phose shilt (trqcethickend by hum-voltcge).
Fig. 54. Summary of waveform analysis for square wave testing of amplifiers.
4 l
CIRCUIT DESCRIPTION
The block diagram, Fig. 55, outlines the circuit break-down of the oscilloscope. Circuit details are obtained byreference to the schematic diaeram.
GENERAL
Basically, the oscilloscope consists of two identicalvertical prqamplifiers, each having its own input attenuatornetwork. The outputs of the vertical preamplifiers can beswitched, as desired, into the main vertical amplifier. Thetype of switching of the CH A and CH B preamplifiers isdetermined by the position of the MODE switch andMODE of OPERATION LOGIC. The main verticalamplifier feeds the VERTICAL OUTPUT AMPLIFIER.which drives the vertical deflection plates of the CRT.
Horizontal deflection is provided by the horizontalamplifier. Drive to the horizontal amplifier is furnished bycalibrated sweep speed circuits or by the signal from the CHB preamplifier when X-Y operation is selecied.
All supply voltages are fully regulated and a DC-to-DCc-onv^e1tlr provides a regulated 2kV accelerating potential tothe CRT.
VERTICAL PREAMPLIFIERS
Channel A and Channel B preamplifiers contain identicalcircuitry and circuit operation is the same for both.
The vertical attenuator has two sections. The firstsection of the attenuator provides ratios of 1: I, 10: l,100: l, 1000: l. The second section provides ratios of 2:land 5:1. The combined effect of the two sections is toprovide the vertical attenuator ratios in a l-2-5 sequence.
The vertical preamplifier consists of FET input tran-sistors Ql02 and Ql03 and transistors Ql04 thru Q109.FET's Ql02 and Q103 form a balanced differentialJllplifier pair with output signals of opposite polarity.VRl0l is the front panel DC balance control and VRtfZan internal balance control. The output of Q102 and Ql03is applied to emitter followers Ql04 and Q105 which lowerlhe o_utpuJ impedance to drive conventional amplifier stageQ106 and Q107. VR105 and VRl06 are balance pots forthe l l2 and ll5 attenuator positions. The VARIABLEcontrol adjusts the gain of Q106 and Q107 while VRl0lprovides a DC component to move the trace verticallyacross the screen. Amplif ier gain is adjusted by VRl07 in'the emitter circuit of Q 108 and Q 109 to provide thecorrect deflection factor for accurate voltage measure-ments.
The trigger amplif ier Ql19 and Q120 amplif ies the signala the emitter of Q108 and Q109 and provides a portion oftne signal to the trigger circuits.
f_hg only difference between CH A and CH B pre-amp[flers is that the MODE switch reverses the polarity ofthe CH B signal when in the A-B position.
MODE LOGIC
The mode of operation (CH A, CH B, A & B, A + B, A -B) is control led by tCl0l and lc l02 and diodes Dl0l -D 108 in each of the channel preamplif iers.
When CH A is selected, the output of ICI02 Pin 3 is.low,which reverse-biases Dl02 and Dl03 and forward-biasesDl01 and D104, allowing the CH A signal into the mainvertical amplifier. At the same tine lcl02 Pin I I output is
42
high which forward-biases Dl06 and Dl07 and reverse-biases D105 and D108 prohibit ing CH B signal from themain amplifier. For CH B, the reverse is true. When A & Bis selected, both channels are alternately switched by IC l0l7t a _r_a!e equal to the chopping oscillator frequency(200kHz). For A + B and A B, both channels ar-esimultaneously applied to the main amplifier. When X-yoperation is selected, CH A is turned on and CH B isswitched to the horizontal amplifier.
VERTICAL AMPLIFIER
The selected signal from the preamplifiers is then appliedto the vertical amplifier which consists of Q123,Q124 andICl03- The signal level is increased to drive the outputamplifier.
The output amplifier consists of transistors Q30l thruQ306 where the signal is amplified to the levels required todrive the vertical deflection plates of the CRT.
TRIGGER CIRCI.IIT
_ f!. trigger source, either CH A or CH B, is selected bySW20l. Selecting CH A as the source enables triggeramplif ier _Ql19 and Ql20 and CH B enables trigger{nplifier Q12l and Ql22.The trigger amplifier selected isfed thru transistor switch Q219. Q2l9 is on in all positionsof the SWEEP TIME/CM switch except CH B.
SYNC AMPLIFIER AND INVERTER
Transistors Q20l , Q202, Q203, and Q2M are connectedas a differential {nplifier. The trigger signal is applied toemitter follower Q20l and routed to the base of-Q202 orq?91_depending upon the position of the SyNC switch,SW202, r or - respectively.-Emitter follower e2O4 adds aDC Jevel to the tlgel signal depending upon the positionof the TRIGGER LEVEL control.
When VIDEO+ or - is selected, the output of e203 isrouted to the SYNC SEPARATOR circuii consisting ofQ205 and Q206. Q205 is biased near cutoff. e205 is leldcutoff by- the negative voltage developed across e205corresponding to an average value of ihe input signal.Positive-going pulses drive Q205 out of cutoff. the outputof. Q205 corresponds to the sync tips of the compoiitevideo signal.
When in FRAME positions of time base switch (.lmS to.5 SEC), capacitor C2O7 is switched in by Q206 to filterout the horizontal sync pulses.
The trigger signal passes thru emitter follower e207 andthe SCHMITT TRIGGER circuit consisting of two gates ofIC201. The output pulses from IC20l PIN A clock theSWEEP CONTROL flip-flop [C2OZ. On the negative edge ofthe clock waveform, the Q output goes low, turnin[ offQ2l3 to initiate to sweep.
Transistors Q216 and Q2l7 and the timing capacitorsand resistors selected by the SWEEP TIME/CM iwiti:h forma MILLER INTEGRATING circuit to provide a linear rampvoltage. The sweep ramp from the collector of e2l7 is feito the RS flip-flop consisting of two gates from IC20l thrutransistor Q2l 1 and Q212.
As soon as the Q output of lC2O2 goes low, the reset of1C202 is held low by Q21 I to exclude any new clock pulsesuntil the sweep ramp is terminated. Transistor e2l2 turnson and sets pin l3 of lC2O2 LOW which turns e2l3 on andterminates the sweep.
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Transistors Q208, Q209, and Q2l0 form the AUTOTRIGGER SENSE switch. When the TRIG LEVEL controlis adjusted so that the slope is not triggered, transistor Q8and Qg produce pulses which keep Q2tO ON. The oncondition is applied to the RESET of 1C202. A low on thereset of 1C202 allows a sweep to recirculate at a ratedetermined by the resistor and capacitor selected by theTIME/CM switch.
The sweep ramp from the collector of Q2I7 is applied tothe input of the horizontal amplifier consisting of Q218,Q220,QZZI - Q225.
When in the CH B position of SWEEP TIME/CM switch,mode, transistor Q2l9 is turned off thru 1C203 and the CH'B signal is applied to Q22O and to the horizontal amplifier.The output of transistorS Q224 and Q225 is applied to thehorizontal deflection plates of the CRT.
CALIBRATION ADJU STMENTS
The calibration adjustments outlined here are thosewhich can be performed with a minimum of specialized testequipment. Additional internal adjustments of frequencycompensation and horizontal sweep linearity should not beattempted without complete service information andspecified test equipment. Requests for complete serviceinformation for this oscilloscope should be addressed to:
Sert'.iee Departrnent
B & K-Precision Product GroupDYNASCAN CORPORATION
2815 West Irving Park RoadChicago, Illinois 60618
Internal adjustments outl ined in the calibration pro-cedure can be located by reference to Fig. 56 and 57.
HOUSING REMOVAL
l. Remove 6 screws, 2 on left side, 2 on right side, and 2on top.
230 VAC OPERATION
l. Remove housing from scope.
2. Remove voltage selector plug (see Fig. 58).
3. Rotate plug l80o and re-insert plug.
4. Replace 0.7A fuse with 0.3A fuse.5. Replace housing.
GRATICULE REMOVAL
l. Grasp bezel with both hands at top and bottom. Pullbezel uniformly forward to unlock mounting legs fromfront panel. Caution should be used to keep bezelparallel to front panel when removing, to avoid break-age of mounting legs.
Lift off graticule from bezel.
Reinsert graticule on bezel and snap bezel into frontpanel mounting holes.
ASTIGMATISM ADJUSTMENT
1. Set SWEEP TIME/CM switch to CH B.2. Wirh INTENSITY at midrange, adjust FOCUS and
ASTIG for sharpest, roundest spot.
CAUTION
Never allow a small spot of high brilliance to remainstationary on the screen for more than a few seconds. Thescreen may become permanently burned.
CH A AND CH B DC BALANCE
l. Display single horizontal trace (CH A or CH B).
2. Adjust CH A or CH B POSITION control to center thetrace vertically on the CRT.
3. Rotate the VARIABLE control from maximum CCWto maximum CW while observing the trace.
4. lf the trace moves vertically more than 5mm whileperforming STEP 3, adjust the CH A or CH B DC BAL(front panel screwdriver adjustment) so that thevertical movement of the trace does not exceed 5mmwhile performing STEP 3.
I 12 & l /5 ATTENUATOR BALANCE
l. Position trace to vertical center of screen CH A or CHB, with .01 V/CM and input at GND.
2. Switch to .02 V/CM and adjust VRl05 (CH A) orVRl08(CH B) unt i l t race is at vert ical center.
3. Switch to ,05 V/CM and adjust VRl06 (CHA) orVRl09 (CH B) unti l trace is at vertical center.
HORIZONTAL POSITION ADJUSTMENT
1. Set CH B and < > POSITION controls to mechanicalcenter.
2. Display single horizontal trace.3. Adjust VR206 to start trace at left edge of graticule
scale.4. Set SWEEP TIME/CM switch to CH B.5. Adjust VR205 so spot on CRT is centered horizontally'6. CH B POSITION control should deflect spot 4 CM or
more from center when turned full CW to CCW. SetSWEEP TIME/CM switch to I gS and repeat for < >POSITION control.
VERTICAL GAIN ADJUSTMENT
The following adjustments should be attempted only if asquare wave generator with l% or better amplitude ac-curacy is available.
l. S€t CH A and CH B VOLTS/CM switches to.01V/CMand set CH A and CH B VARIABLE controls to CAL(fully clockwise).
2. Apply I kHz square wave of 50 mV peak-to-peak intoCH A input connector. Set mode switch to CH A.
3. Adjust VRl07 for exactly 5 CM of deflection on CRT.
4. Repeat steps 2 and 3 for CH B and adjust VRl l0 for 5CM deflection.
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Fig. 56. Calibration diagram, vertical amplifier board.
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Fig. 58. Calibration diagam, power supply board.
P O W E R S U P P L Y B O A R D
ROTATE PLUG TOC H A N G E V O L T A G E
240 VAC
1 20 VAC
o . 7 A - 1 2 0 V A Co.3A- 240 VAC
T C 3 O 1 - M I D F R E O U E N C YT C 3 0 2 _ U N B L A N KV R 3 0 5 _ H I G H F R E Q U E N C YV R 3 0 6 - 1 . 9 K V A D J .V R 3 O 7 _ I N T E N S I T Y A D J .V R 3 O B _ Y D E F L E C T I O NV R 3 O 9 - 1 9 5 V A D J .
F U S E :
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WARRANTY SERVICE INSTRUCTIONS
l. Refer to the MAINTENANCE section of your B & K-Precision instruction manual foradjustments that may be applicable.
2. lf the above-mentioned procedures do not correct the problem you are experiencingwith your unit, pack it securely (preferably in the original carton or double-packed).Enclose a letter describing the problem and include your name and address. Deliver to,or ship PREPAID (LIPS preferred) to the nearest B & K-Precision authorized serviceagency (see list enclosed with unit).
If your list of authorized B & K-Precision service agencies has been misplaced, contactyour local distributor for the name of your nearest service agency, or write to:
Service Deprtment
B & K-Precision Product GroupDYNASCAN COPPORATION
2815 West Irving Park RoadChicago, Illinois 6061 8
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LIMITED ONE-YEAR WARRANTY
DYNASCAN CORPORATION warrants to the original purchaser that its B & K-PRECISION product, and the component parts thereof, will be free from defects inworkmanship and materials for a period of one year from the date of purchase.
DYNASCAN will, without charge, repair or replace, at its option, defective product or com-ponent parts upon delivery to an authorized B & K-PRECISION service contractor or the fac-tory service department, accompanied by proof of the date of purchase in the form of a salesreceipt.
To obtain warranty coverage, this product must be registered by completing and mailing theenclosed warranty registrat ion card to DYNASCAN, B & K-PRECISION, P. O. Box 35080,Chicago, Illinois 60635 within five (5 days) from the date of purchase.
EXCLUSIONS; THIS WARRANTY DOES NOT APPLY IN THE EVENT OF MISUSEOR ABUSE OF THE PRODUCT OR AS A RESULT OF UNAUTHORIZEDALTERATIONS OR REPAIRS. IT IS VOID IF THE SERIAL NUMBER IS ALTERED,DEFACED OR REMOVED.
DYNASCAN shall not be liable for any consequential damages, including without limitationdamages resulting from loss of use. Some states do not allow limitation of incidental or conse-quential damages, so the above limitation or exclusion may not apply to you.
This warranty gives you specific rights and you may also have other rights which vary fromstate to state.
For your convenience we suggest you contact your distributor, who may be authorized tomake repairs or can refer you to the nearest service contractor. If warranty service cannot beobtained locally, please send the unit to B & K-PRECISION Service Department,2Sl5 WestIrving Park Road, Chicago, Illinois 60618, properly packaged to avoid damage in shipment.
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o 8478 pRtNTED tN JAPAN 850-2823-00 (c)
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DYNASCANCORPOFrANON
6460 West Cortlond Street
Chicogo, lllinois 60635
480.182-9-0018
