Welder User Manual

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POWER MIG 255
Section F-1 Section F-1
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
Main Transformer Test ..........................................................................................F-11
Rectifier Diode Bridge Test...................................................................................F-15
Static SCR Rectifier Assembly Test .....................................................................F-19
Active SCR Rectifier Assembly Test.....................................................................F-23
Wire Drive Motor and Tachometer Feedback Test...............................................F-27
Oscilloscope Waveforms
Normal Open Circuit Voltage Waveform ..............................................................F-31
Typical Output Voltage Waveform - Machine Loaded..........................................F-32
Abnormal Output Voltage Waveform - Machine Loaded One Output SCR Not Functioning ............. F-33
Abnormal Open Circuit Voltage Output Capacitor Bank Not Functioning...........F-34
Typical SCR Gate Voltage Waveform ...................................................................F-35
Replacement Procedures
Control PC Board Removal and Replacement.....................................................F-37
Wire Drive Assembly Removal and Replacement................................................F-41
SCR Output Rectifier Removal and Replacement ...............................................F-45
Capacitor Bank Removal and Replacement ........................................................F-49
Main Transformer and Output Choke Removal and Replacement ......................F-51
Fan Motor and Fan Removal and Replacement ..................................................F-55
Retest After Repair......................................................................................................F-57