ESAB Precision Plasmarc EPP-450 Manuel D'instructions page 50

section 6
NEG Plate
Electrode Plate
troubleshooting pos plate
Location of Pos. Plate
Location of fuses F8 and F9
troubleshooting electrode plate
Bus
Diode Rectifier
2. If fuses F8 and/or F9 were open in the first step, make two
A. Measure resistance between the NEG Plate and
POS Plate
B. Measure between NEG Plate and BR "C" bus.
If resistance is 2 ohms or less in either case, replace all the
2. If fuses F8 and/or F9 were open in the first step, make two
A. Measure resistance between the POS Plate and BR
"B" bus.
B. Measure between POS Plate and BR "C" bus.
If resistance is 2 ohms or less in either case, replace all the
diodes on the POS Plate.
Cathode Leads
2. Check resistance between Electrode Plate and the parallel
Repeat procedure for D27 and D28. Replace only shorted
diodes.
blocking diodes d25, d26, d27 and d-28
50
troubleshootinG
1. Check ohms between NEG Plate and BR " A" Bus. A reading
of 2 ohms or less indicates one or more shorted diodes.
Replace all Diodes on NEG Plate.
more ohmmeter readings.
BR "B" bus.
diodes on the NEG Plate.
1. Check ohms between POS Plate and BR " A" Bus. A reading
of 2 ohms or less indicates one or more shorted diodes.
Replace all Diodes on POS Plate.
more ohmmeter readings.
1. Visually inspect for ruptured or burned diodes. Replace
only those damaged.
pig tails (cathode leads) of D25 and D26. If reading is 2
ohms or less, disconnect leads from bus and check each
diode. Replace only shorted diodes.