ESAB EPP-400 Manuel D'instructions page 300

section 6
NEG Plate
Electrode Plate
troubleshooting pos plate
Location of Pos. Plate
Location of fuses F8 and F9
D25,26
Bus
Diode Rectifier
POS Plate
D27,28
Cathode
Leads
300
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.
2. If fuses F8 and/or F9 were open in the first step, make two
more ohmmeter readings.
A. Measure resistance between the NEG Plate and
BR "B" bus.
B. Measure between NEG Plate and BR "C" bus.
If resistance is 2 ohms or less in either case, replace all the
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.
2. If fuses F8 and/or F9 were open in the first step, make two
more ohmmeter readings.
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.
1. Visually inspect for ruptured or burned diodes. Replace
only those damaged.
2. Check resistance between Electrode Plate and the parallel
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.
Repeat procedure for D27 and D28. Replace only shorted
diodes.
troubleshootinG