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TROUBLESHOOTING & REPAIR
F-28 F-28
SQUARE WAVE TIG 275
STATIC SCR TEST (continued)
3. Using an analog ohmmeter, test the resis-
tance from anode to cathode of SCR1.
Reverse the meter leads and check from
cathode to anode of SCR1. See Figure F.5.
If a low resistance is indicated in either
direction, SCR1 is faulty. Replace the SCR
Bridge Assembly. See
SCR Bridge
Assembly Removal and Replacement.
4. Repeat Step #3 testing SCR2, SCR3 and
SCR4.
5. To further check the SCR’s functions, use an
SCR tester and proceed to the
Active SCR
Test.
NOTE: Also check diode D1.
6. Replace plug J1 on the control board.
7. Replace the case top and left side.
FIGURE F.5 – SCR TEST POINTS
