Troubleshooting & repair – Lincoln Electric POWER MIG 255 SVM144-B User Manual

Page 63

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POWER MIG 255

TROUBLESHOOTING & REPAIR

F-25

F-25

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8. Use a commercial SCR tester or con-

struct the tester circuit shown in Figure
F.8. One 6-volt lantern battery can be
used. R1 and R2 resistor values are
±10%. Set voltmeter scale low, at
approximately 0-5 volts or 5-10 volts.

a. Test the voltage level of the battery.

Short leads (A) and (C). Close
switch SW-1. Battery voltage
should be 4.5 volts or higher. If
lower, replace the battery.

FIGURE F.8 — SCR TESTER CIRCUIT

AND SCR CONNECTIONS.

6. Disconnect leads X2 and X3 (braided

copper strap) from the negative capaci-
tor bank buss bar using a 1/2 in. open
end wrench. See Figure F.7.

FIGURE F.7 — LOCATION OF

LEADS X2 AND X3.

7. Separate leads X2 and X3 from the

negative capacitor bank buss bar. Be
sure there is no electrical contact.

NOTE: DO NOT DISASSEMBLE THE SCR
RECTIFIER HEAT SINK ASSEMBLY.

ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)

NEGATIVE

CAPACITOR

BANK BUSS

BAR

LEADS X2 AND X3

CONNECTION

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