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TABLE OF CONTENTS
-TROUBLESHOOTING & REPAIR SECTION-
Troubleshooting & Repair Section.......................................................................................Section F
How to Use Troubleshooting Guide............................................................................................F-2
PC Board Troubleshooting Procedures and Replacement.........................................................F-3
Troubleshooting Guide................................................................................................................F-4
Test Procedures ........................................................................................................................F-20
Input Power Factor Capacitor Voltage Check and Discharge Procedure..........................F-20
ARC Start Trigger Circuit Test.............................................................................................F-22
Power Board Test ...............................................................................................................F-25
Input Contactor Test...........................................................................................................F-28
Pilot Transformer Test.........................................................................................................F-32
Feed-Thru PC Board Test...................................................................................................F-34
Protection PC Board Test...................................................................................................F-38
Main Transformer Test ........................................................................................................F-41
Control Transformer (T5) Voltage Test ................................................................................F-44
Control Board Test..............................................................................................................F-47
Static SCR Test...................................................................................................................F-51
Active SCR Test..................................................................................................................F-54
Oscilloscope Waveforms ..........................................................................................................F-58
Normal Open Circuit Voltage Waveform (DC Stick Mode).................................................F-58
Normal Open Circuit Voltage Waveform (AC Stick Mode) .................................................F-59
Normal Open Circuit Voltage Waveform (DC TIG Mode) ...................................................F-60
Normal Open Circuit Voltage Waveform (AC TIG Mode)....................................................F-61
Typical Output Voltage Waveform – Machine Loaded (DC TIG Mode) ..............................F-62
AC TIG Mode (Balanced Waveform) ..................................................................................F-63
Abnormal Open Circuit Voltage – (DC TIG Mode, One
Output SCR Not Functioning).......................................................................................F-64
Abnormal Open Circuit Voltage – (AC TIG Mode, One
Output SCR Not Functioning).......................................................................................F-65
Replacement Procedures..........................................................................................................F-66
Control PC Board Removal and Replacement...................................................................F-66
Power PC Board Removal and Replacement ....................................................................F-68
Input Contactor (C1) Removal and Replacement ..............................................................F-70
Fan Motor and Blade Removal and Replacement.............................................................F-73
Output Rectifier Removal and Replacement......................................................................F-75
SCR Removal and Replacement........................................................................................F-78
Rest after Repair .......................................................................................................................F-84
Section F-1 Section F-1
SQUARE WAVE TIG 355