Lincoln Electric SVM169-A service manual Figure F.6 SCR Gate Locations

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F-27 TROUBLESHOOTING & REPAIR F-27

ACTIVE SCR TEST (continued)

	SCR2 CATHODE
SCR1 ANODE	SCR3 CATHODE
	SCR4 ANODE

SCR1 CATHODE/SCR2 ANODE

SCR3 ANODE/SCR4 CATHODE

PLUG J2

3		4
	SCR3		SCR4
	SCR1		SCR2
1		2

S24018-4 (INSERTION SIDE)

SCR GATE LEADS/TEST POINTS

FIGURE F.6 SCR GATE LOCATIONS

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6.Connect SCR into the test circuit as shown (A) lead to anode (C) lead to cathode and (G) lead to the gate.

7.Close switch SW-1 (switch SW-2 should open), voltmeter should read zero. If the voltmeter reads higher than zero the SCR is shorted.

8.With switch SW-1 closed, close switch SW-2 for two seconds and release. The voltmeter should read 3 to 6 volts before and after switch SW- 2 is released. If the voltmeter does not read, or reads only while SW-2 is depressed, the SCR or battery is defective (repeat Battery Test Procedure above).

9.Open switch SW-1, disconnect the gate lead (G) and reverse the (A) and

(C)leads on the SCR. Close switch SW-1. The voltmeter should read zero. If the voltage is higher than zero, the SCR is shorted.

10.Replace SCR Bridge Assembly if any SCRs do not pass the test in Step #3. See SCR Bridge

Assembly Removal and Replacement.

11.Replace plug J2 into the control board.

12.Replace the case wrap-around cover.

PRECISION TIG 185