ESAB EPP-400 Manuel D'instructions page 296

section 6
6.3.5 fuses f1 and f2 blown
problem
Fuses F1 and F2 blown.
6.3.6 intermittent, interrupted or partial operation
problem
Works OK at 250A or less- Over current
– Faulty Left Side
possible cause
Process controller ignites pilot arc too
soon after providing the "Contactor
On" signal
Faulty negative (Electrode) output cable
shorting to earth ground.
Shorted freewheeling diode.
One or more shorted diode rectifiers
(D13-D18) on "POS Plate".
One or more shorted diode rectifiers
(D7-D12) on "NEG Plate".
possible cause
Loose or unplugged connector at left
PWM / Drive PCB (PCB2)
Faulty left PWM / Drive PCB
Check voltage between P5-1 and P5-
2 at the left PWM / Drive PCB (PCB2).
Should be 20V AC. Between P5-1 and
P5-3 should be 40V AC. If not the control
transformer (T5) is faulty.
296
troubleshootinG
action
Process controller must allow at least
300MS to lapse between the applica-
tion of the "Contactor On" signal and
the ignition of the pilot arc. Fix process
controller logic and replace diodes.
Repair cable
Replace shorted freewheeling diode
and F1-F2
Replace all diode rectifiers on the "POS
Plate".
Replace all diode rectifiers on the "NEG
Plate".
action
Secure connector
Replace right PWM / Drive PCB P/N
38030
Replace control transformer T5