Basic Troubleshooting Skill
Guide to troubleshooting techniques of Comba active products
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Objective To develop an understanding on some
basic troubleshooting techniques that can be employed with simple test tools.
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Topics1. Introduction
i. Why the need for troubleshooting?ii. Fault Categoryiii. Test tools
2. Types of Troubleshooting Techniquesi. Visual Inspection ii. Test & Measurement methodiii. Comparison Method
3. Fault Tracing4. Fault Symptoms5. Alarm Check List
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Introduction Troubleshooting is a problem solving
technique that systematically seeks out the root of the problem so that it can be rectified.
Why the need for troubleshooting? Identify genuine and bogus faults Reduce repair time & cost for return
goods Reduce network coverage downtime
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Fault CategoryClassification of Faults: Hardware
Usually associated with active modules such as PSU, PA, LNA and MCU
Active modules are subjected high power and heat
RF Interferences Interferences caused by radio environment High PIM interferences
Software Software glitches appearing on OMT/OMC Can be resolve by applying software patches
Mechanical Damaged parts such as broken pins/PCB/connectors Dry contact due to poor soldering or loose connector
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Test Tools Spectrum Analyzer with tracking generator function Rhode &
Schwarz, model FSH3 or equivalent 40dB Attenuator Signal Generator Rhode & Schwarz, model SML 03 or equivalent Digital Multimeter Flexible jumper cable with N-male connectors x2
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Techniques Test & Measurement Method
Measures the DL and UL output power at the MT and DT port respectively
Check for abnormal or no output power level Measures the AC and DC voltages of the PSU
Comparison Method Swap out the suspected faulty module with a new module and
compare the before and after effect Use a spare unit as reference to determine which module is faulty
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Techniques Visual Inspection
Visually check for burnt mark, water seepage, corroded or brokenparts, loose connectors and missing components
Check LED indicators on MCU board and PSU for alarms or abnormal operation
Determine type of alarms using OMT
Water near PSU
Corrosion on PCB
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Techniques Signal Tracing
Trace the input signal at the output port of each module to identify the faulty module
1
2
A
B
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Fault Symptoms DL / UL PA module faulty :
PA and PLL alarms activated No / poor network coverage in repeater/booster cell vicinity High call setup failure High drop calls
LNA faulty LNA alarm activated High call setup failure No / poor network coverage in repeater/booster cell vicinity
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Fault Symptoms Main Control Unit faulty
Multiple alarms and corrupted data appearing on MCU Fail to connect to equipment via local and remote connections
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Fault Symptoms Power Supply Unit faulty :
Power Down and Power Failure alarms activated Red LED flashing, Green LED off, clicking sound Fail to connect to equipment via local and remote connections No / poor network coverage in repeater/booster cell vicinity
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Downlink PA Test
Set the signal generator to EUT inband DL Freq X and output power level to -70dBm
Set the Spectrum Analyzer to monitor centre frequency at Freq X
Measured peak signal level should be approx (-70dBm+Max Gain-30dB-2dBm) after passing through the 30dB attenuator
Repeat the test for other channels, if necessary
Configure the EUT as follows: PA Switch = ON. Downlink CH No.1 = Freq X. Downlink Post-ATT 1 = 0. Downlink Pre-ATT 1 = 0.
EUT
30dB
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Uplink PA Test
EUT
30dB
Set the signal generator to EUT inbandUL Freq X and output power level to -80dBm
Set the Spectrum Analyzer to monitor centre frequency at Freq X
Measured peak signal level should be approx (-80dBm+Max Gain-30dB-2dBm) after passing through the 30dB attenuator
Repeat the test for other channels
Configure the EUT as follows: PA Switch = ON. Uplink CH No.1 = Freq X. Set all UL ATT = 0.
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Power Supply Unit Test Measures main supply AC voltages 110/220V Measures DC voltages +5V,+9V and +25V
+9V+5V+25V
GND
PSU
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Remote Connection Failure Symptom 1:
Modem LED is not flashing LED indicator L4/H3 on MCU board is on
Possible Causes: SIM card does not have circuit switch data Modem antenna is not connected
Remedy Actions: Activate circuit switch data for SIM card Connect an antenna to the DT port or to the modem antenna port
of the equipment
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Remote Connection Failure Symptom 2:
Number dialed is not in use or not available Busy tone
Possible Causes: Modem failed to log on to cellular network SIM card does not have circuit switch data Modem antenna is not connected High network traffic
Remedy Actions: Activate circuit switch data for SIM card Ensure L4(Red)/H3(Red) indicator on MCU board is off after MCU
completes initialization. If L4/H3 remains on, press the reset button on the MCU board to re-initialize modem
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LED indicators layout on older generation MCU board
LED indicators layout on new generation MCU board
Remote Connection Failure
PSUDT Coupler ON/OFFSwitch
DistributionBoard
MCU
MT Coupler
Modem
DT MT
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Remote Connection Failure Symptom 3:
Connection via wireless modem is fine but fail to connect via PSTN modem
Possible Causes: Telephone line does not support circuit switch data SIM card has data feature enabled only
Remedy Actions: Configure the SIM card to accept voice call Ensure telephone line supports circuit switch data
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Remote Connection Failure Symptom 4:
Error message Read parameters failed (for CSP3 model)
Possible Causes: SIM card number not added to Phone No. Check List
Authorize users phone nos.
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Remote Connection Failure Remedy Actions:
Add SIM card no into the list Disable the Phone No. Checking feature
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Safety Precautions Remove power plug from socket before replacing the PSU Switch off PSU before changing out any electrical parts such as
MCU board, PA and LNA Use proper tools to remove any parts/modules Label the cables or connectors, if necessary, before removing
any faulty module Ensure that the correct spare module is used for replacement Ensure all connectors and cables are correctly connected before
turning on the equipment Apply a fresh layer of heat transfer silicon beneath the new
module to achieve optimum heat transfer via chassis body.
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Component Layout (RA-2100)
ALARMS CHECK LIST
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Alarm Check ListType of Alarm Possible Cause Remedy Action
Power Down /AC Power Failure
- AC breaker tripped - Reset breaker
- Mains power failure - Restore mains power supply
- Power Supply Unit(PSU) faulty
- Replace blown fuse / PSU
Power Failed /DC Power Fault
- PSU faulty or fuse blown - Replace blown fuse / PSU
MCU Battery Fault /Li-ion Battery Fault
- Batteries are over-discharged - Connect batteries to PSU for charging
- Batteries are damaged - Replace batteries
DL PA - Over drive of PA module - Increase DL ATT value
- DL PA module is faulty - Replace PA module
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Alarm Check ListType of Alarm Possible Cause Remedy Action
DL VSWR - RF cable is not properlyconnected to MT port
- RF cable is damaged
- Check connection between cable and MT port
- Sweep feeder cable and DASwith Site Analyzer.
Optical Tx/Rx - Optical transceiver is faulty
- Fiber optical cable is damaged
- Replace Optical transceiver module
- Replace fiber optical cable
Li-ion Battery Low - Battery voltage is below threshold setting
- Connect batteries to PSU for charging
PA Over-Temperature - PA modules over heateddue to high input power
- PA module may be faulty
- Reduce input power level
- Replace faulty PA module
UL LNA Fault - Damaged by high inputpower
- LNA is faulty
- Replace LNA
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Alarm Check ListType of Alarm Possible Cause Remedy Action
UL Working Channel PLL 1
- UL PLL circuit is faulty - Replace UL PA module
DL Working Channel PLL 1
- DL PLL circuit is faulty - Replace DL PA module
DL Output Power Low
- Downlink output signal is below Power Low Threshold (DL out)
- Weak/No DL signal received
- Low gain setting for DLPA
- Adjust Power Low Threshold (DL out) to a suitable value
- Ensure BTS is transmitting
- Reduce Master ATT (DL) to increase output power
DL Input Power Overload
- DL Input power levelexceeds threshold value
- DL input power too strong
- Reduce input power level
- Adjust DL Input Power Overload Threshold value
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Alarm Check ListType of Alarm Possible Cause Remedy Action
Chassis Lock/Door Open
- Chassis door is open
- Micro switch has drycontact
-Close chassis door
- Ensure micro switch is notobstructed.
Master/Slave Unit Link - No connection betweenMaster and Slave unit
- Check cable connection between Masterand Slave unit.
External - One or more of externalalarms are triggered
- Clear external alarms
The End
Thank youThank you
Basic Troubleshooting Skill ObjectiveTopicsIntroductionFault CategoryTest ToolsTechniquesTechniquesTechniquesFault SymptomsFault SymptomsFault SymptomsDownlink PA TestUplink PA TestPower Supply Unit TestRemote Connection FailureRemote Connection FailureRemote Connection FailureRemote Connection FailureRemote Connection FailureRemote Connection FailureSafety PrecautionsComponent Layout (RA-2100)ALARMS CHECK LISTAlarm Check ListAlarm Check ListAlarm Check ListAlarm Check ListThe End