Lincoln Electric IM474 IDEALARC DC-400 - Manual (Page 32)

E-7 TROUBLESHOOTING E-7
IDEALARC® DC-400
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact your
Local Lincoln Authorized Field Service Facility for technical troubleshooting assistance before you proceed.
CAUTION
REMOTE CONTROL CHECK
Disconnect the remote output control and connect an
ohmmeter across 75 to 76 and rotate the rheostat in
the remote control. The resistance reading should go
from zero to 10K ohms. Repeat with ohmmeter
across 75 and 76 with same results. Connect ohm-
meter across 75 and 77. The reading should be 10K
ohms. A lower reading will indicate a shorted or par-
tially shorted rheostat. A very high reading will indi-
cate an open rheostat. In either of the last two cases,
replace rheostat. Check cable for any physical dam-
age.
POWER RECTIFIER BRIDGE ASSEMBLY
CHECKING PROCEDURE
1. Bridge and Device Isolation (See the instruc-
tion manual parts list for the exact location.)
Disconnect the following leads from the bridge,
shown in Diagram 1:
a) Unplug P3 (G1, G2, G3 and 204) from the
Control PC Board.
b) Unplug P5 from the Snubber PC Board.
c) Secondary leads X1, X2, and X3 from the
anodes of the SCRʼs and cathodes of the
diodes.
d) Disconnect positive bridge lead from shunt and
positive capacitor bank lead and from lug with
triple 204 leads.
e) Perform the following steps 2 and 3. If diodes
and SCRʼs are not shorted, bridge test is com-
pleted. If any device appears shorted, discon-
nect the cathode lead of each diode (4 total)
and repeat Steps 2 and 3.
2. Power Diode Test
a) Establish the polarity of the ohmmeter leads
and set to X10 scale.
b) Connect the ohmmeter positive lead to anode
and negative lead to cathode.
c) Reverse the leads of the ohmmeter from
Step b.
d) A shorted diode will indicate zero or an equally
low resistance in both directions. An open
diode will have an infinite or high resistance in
both directions and a good diode will have a
low resistance in Step b and Step a much high-
er resistance in Step c.
3. Power Silicon Controlled Rectifier Test
a) Connect the ohmmeter (set to m X10 scale)
leads to the anode and cathode.
b) Reverse the leads of the ohmmeter from Step
a.
c) A shorted SCR will indicate zero or an equally
low resistance in one or both directions.
d) Establish the polarity of the ohmmeter.
Connect the positive lead to the gate and the
negative lead to the cathode.
e) An open gate circuit will have an infinite or high
resistance. A good gate circuit will read a low
resistance, but not zero ohms. If gate circuit
reads zero ohms, check gate harness for
shorts between gate leads and 204 before
replacing SCR.
ELECTRIC SHOCK can kill.
• Have an electrician install and ser-
vice this equipment.
• Turn the input power off at the fuse
box before working on equipment.
• Do not touch electrically hot parts.
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WARNING