Lincoln Electric COMMANDER 400 SVM133-B Service Manual page 98

F-44
STATIC SCR/DIODE RECTIFIER BRIDGE TEST (continued)
REMOVE
INSULATING PAINT
9. Remove the red insulating paint from the
heat sink test points. See Figure F.16.
NOTE: Do not disassemble the heat sink.
10. Measure the resistance from the anode to
the cathode of SCR A, using an analog
volt/ohmmeter (multimeter) set at R x 1000
scale. See Figure F.16.
a. Reverse the meter leads and measure the
resistance from the cathode to the anode
of SCR A. See Figure F.16.
b. If a low resistance is measured in either
meter polarity, SCR A is faulty. Replace
SCR A.
11. Test the resistance of SCR B and SCR C
using the same procedure described in Step
10.
12. Measure the resistance of diode DD from
anode (+probe) to cathode (-probe) using an
analog ohmmeter set at R x 1000 scale. The
resistance should be low. See Figure F.16.
a. Reverse the meter leads and measure the
resistance from cathode (+probe) to
anode (-probe) of diode DD. The resis-
tance should be high. See Figure F.16.
TROUBLESHOOTING & REPAIR
FIGURE F.16 – HEAT SINK AND SCR TEST POINTS
DIODE DD
COMMANDER 400
DIODES DA, DB, DC
b. If a low resistance is measured in both
meter polarities, diode DD is shorted.
Replace diode DD.
c. If a high resistance is measured in both
meter polarities, diode DD is open.
Replace diode DD.
13. Test diodes DA, DB and DC for proper oper-
ation using the same procedure described in
Step 12.
14. Reconnect all leads and molex plugs.
15. If this test did not identify the problem or to
further test the SCRs, go to the Active SCR
Test.
If the test is complete, connect plug J6 to the
control board and plug J30 to the snubber
board and reconnect lead #204B to resistor
R1. Replace the covers to the two boards.
Replace all case covers.
Cover Removal and Replacement proce-
dure.)
F-44
ANODE
CATHODE
(See the Case