IMA 474
DC-400
Page 21
TROUBLE
CAUSE
WHAT DO DO
A. Input contactor (CR1) chatters.
1. Faulty input contactor (CR1).
1. Repair or replace.
2. Low line voltage.
2. Check input power.
B. Machine input contactor does
1. Supply line fuse blown.
1. Replace if blown - look for reason
not operate.
first.
2. Contactor power circuit dead.
2. Check control transformer T2 and
associated leads.
3. Broken power lead.
3. Check input voltage at contactor.
4. Wrong input voltage.
4. Check voltage against instructions.
5. Open input contactor coil.
5. Replace coil.
6. Power “l/0” switch (S1)
6. Replace switch.
not closing.
C. Machine input contactor
1. Trigger circuit between #2 and
1. Make sure trigger circuit is being
operates, but no output when
#4 leads is not being closed.
closed.
trying to weld.
2. Electrode or work lead loose or
2. Repair connection.
broken.
3. Open main transformer (T1)
3. Repair.
primary or secondary circuit.
4. Defective Control PC Board.
4. Replace. See Procedure for
Replacing PC Boards.
(Amber thermal protection light is
5. Primary or secondary
5. Check for overheating; make
on)
thermostats open.
sure fan is operating and there is
no obstruction to free air flow.
D. Machine has minimum output
1. Terminals 75, 76 or 77
1. Check 75, 76 or 77 for ground to
and no control.
grounded to positive output.
positive output circuit. Nearly zero
ohms to ground indicates a
grounded circuit. A value greater
than a few thousand ohms is
normal. Self-restoring fuses on PC
Board automatically reset within a
few seconds after ground is
cleared.
E. Machine has high output or
1. Terminals 75, 76 or 77
1. Check 75, 76 or 77 for ground to
pulsing output and no control.
grounded to negative output.
negative output circuit. Nearly zero
ohms to ground indicates a
grounded circuit. A value greater
than a few thousand ohms is
normal. Self-restoring fuses on PC
Board automatically reset within a
few seconds after ground is
cleared.
F. Machine has low output and
1. OUTPUT CONTROL “LOCAL-
1. Check position of switch.
no control.
REMOTE” switch (S2) in
wrong position.
2. OUTPUT CONTROL switch
2. Check switch and replace if faulty.
faulty.
3. Open in feedback circuitry.
3. Check wiring and control PC Board
wiring harness plugs.
4. Faulty Control PC Board.
4. Replace. See Procedure for
Replacing PC Boards.
5. OUTPUT control potentiometer
5. Check and replace potentiometer if
circuit open (lead 75).
faulty. Check wiring of lead #75.
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