Lincoln Electric IDEALARC R3R 500-I Operating Manual page 20

I. REMOTE CONTROL CHECK
The remote control Amphenol pin assignments are: pin C-75, pin
B-76, and pin A-77. Disconnect the remote field control and
connect an ohmmeter across 75 and 76 and rotate the rheostat in
the remote control. The resistance reading should go from zero to
10K ohms. Repeat with triplet across 77 and 76 with same results.
Connect ohmmeter across 75 and 77. The reading should be 10K
ohms. A lower reading will indicate a shorted or partially shorted
rheostat. A very high reading will indicate an open rheostat. In
either of the last two cases, replace rheostat. Check cable for any
physical damage.
J. POWER RECTIFIER BRIDGE ASSEMBLY
CHECKING PROCEDURE
CAUTION
The rectifier bridge tests outlined below will identify the
most common effects found in power diodes or power
silicon controlled rectifiers. If a bridge problem still exists
after test, please call a Lincoln Field Service Shop. Further
evaluation of diodes or silicon controlled rectifiers may
require laboratory equipment.
1. DEVICE ISOLATION (see the instruction manual Parts List
for the exact location)
Disconnect the following leads from the bridge, shown in
Diagram 1:
a. Wiring harness gate leads (G1, G2, G3) from the gate
lead terminals on the Control PC board.
b. AC leads X1, X2 and X3 from the anodes of the SCR's
and cathodes of the diodes.
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c. The 220, 221 and 223 leads from the Snubber PC board.
d. Lead 220 that connects to the latching resistor (R3).
e. The cathode of each diode (4 total).
2. POWER DIODE TEST
a. Establish the polarity of the ohmmeter leads and set to
b. Connect the ohmmeter positive lead to anode and
c. Reverse the leads of the ohmmeter from Step b.
d. A shorted diode will indicate zero or an equally low
K. POWER SILICON CONTROLLED RECTIFIER
TEST
The SCR must be mounted in the heat sink when making this test.
a. Connect the ohmmeter (set to the X10 scale) leads to
b. Reverse the leads of the ohmmeter from Step a.
c. A shorted SCR will indicate zero or an equally low
d. Establish the polarity of the ohmmeter. Connect the
e. An open gate circuit will have an infinite or high
Idealarc R3R 500-I & 600-I
X10 scale.
negative lead to the cathode.
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 a much
higher resistance in Step c.
the anode and cathode.
resistance in one or both directions.
positive lead to the gate and the negative lead to the
cathode.
resistance. A good gate circuit will read a low resistance,
but not zero ohms.
IM 6000