Section TOC
Master TOC
TROUBLESHOOTING & REPAIR
STATIC SCR TEST (continued)
FIGURE F.17 – POWER PC BOARD PLUG LOCATIONS
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J1
SQUARE WAVE POWER
TEST PROCEDURE
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1.Remove the input power to the machine.
2.With the 5/16” nut driver, remove the machine case top and sides.
3.Perform the Input Power Factor Capacitor Voltage Check and Discharge procedure.
4.Remove the output welding cables from the machine.
5.Remove plug J1 from the power PC board. Refer to Figure F.17.
6.Place the polarity switch (S1) in a “DC” position.
7.Remove the red insulating paint from heat sink test points. See Figure F.18. DO NOT DISASSEMBLE THE HEAT SINKS.
8.With the 1/2” wrench, remove the choke lead from the negative plate (top).
9.With the analog ohmmeter, test the resis- tance from anode to cathode of SCR1. Reverse the meter leads and check from cathode to anode of SCR1.
A.If a low resistance is indicated in either direction, SCR1 is faulty. Replace the SCR.
10.Repeat Step 9 testing SCR2, SCR3, and SCR4.
To further check SCR functions, use an SCR tester and proceed to the Active SCR test.
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SQUARE WAVE TIG 355
