Lincoln Electric PRECISION TIG SVM186-A Service Manual page 41

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TABLE OF CONTENTS - TROUBLESHOOTING AND REPAIR
Troubleshooting and Repair.............................................................................................................................F-1
How to Use Troubleshooting Guide .......................................................................................................F-2
PC Board Troubleshooting Procedures and Replacement ....................................................................F-3
Troubleshooting Guide ...........................................................................................................................F-4
Test Procedures
High Frequency Circuit Disable Procedure ..........................................................................................F-15
T1 Transformer Test .............................................................................................................................F-17
Static SCR Test ....................................................................................................................................F-21
Active SCR Test ...................................................................................................................................F-25
Oscilloscope Waveforms
Normal Open Circuit Voltage Waveform-AC TIG Mode .......................................................................F-29
Normal Open Circuit Voltage Waveform-DC TIG Mode.......................................................................F-30
Normal Open Circuit Voltage Waveform-AC Stick Mode .....................................................................F-31
Normal Open Circuit Voltage Waveform-DC Stick Mode .....................................................................F-32
Typical Output Voltage Waveform-Machine Loaded AC TIG Mode .....................................................F-33
Typical Output Voltage Waveform-Machine Loaded DC TIG Mode.....................................................F-34
Typical Output Voltage Waveform-Machine Loaded AC Stick Mode ...................................................F-35
Typical Output Voltage Waveform-Machine Loaded DC Stick Mode...................................................F-36
Abnormal Open Circuit Voltage-DC TIG Mode One SCR not Functioning ..........................................F-37
Replacement Procedures
SCR Bridge Assembly Removal and Replacement .............................................................................F-39
Polarity Switch Removal and Replacement .........................................................................................F-45
High Voltage Transformer Removal and Replacement........................................................................F-49
Main Transformer and Output Choke Removal and Replacement ......................................................F-53
Retest after Repair......................................................................................................................................F-55
PRECISION TIG® 225
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