Lincoln Electric RED-D-ARC DX450 Service Manual page 99

F-55
OUTPUT RECTIFIER BRIDGE TEST (continued)
7. Check for grounds by placing one of the ohm-
meter probes on a clean, unpainted metal sur-
face of the machine. Touch the other probe to
each of the five rectifier terminals. The resis-
tance to chassis ground from each terminal
should be very high, 500,000 (500K) ohms
minimum. If the resistance reading is less than
specified, the rectifier is grounded and should
be replaced.
8. If using a diode checker or a multimeter with
diode check functionality, read and understand
the instructions that accompany your test
equipment.
9. If using an analog ohmmeter, the forward bias
test will indicate low resistance and the reverse
bias test will indicate high resistance. Precise
ohm values for this test will vary depending on
the test equipment used.
W4/W5
W2/W3
W1/W6
TROUBLESHOOTING AND REPAIR
FIGURE F.11 - SHUNT/RECTIFIER LEADS
POSITIVE
NEGATIVE
NOTE: A digital Ohmmeter is not recommended
for this test. A typical digital Ohmmeter
does not provide enough voltage or current
flow to reliably test the diodes used in this
rectifier.
10. Test all of the diode groups per the Table F.2.
11. When the test is complete, reconnect all leads.
12. Perform the Case Cover Replacement
Procedure.
TOP
CENTER
BOTTOM
CHOPPER BOARD
DX450
F-55
OUTPUT
RECTIFIER
BRIDGE