Lincoln Electric DC-655 service manual Figure F.17 Heat Sink Test Points Anode Cathode

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F-40 F-40

TROUBLESHOOTING & REPAIR

ACTIVE SCR TEST (continued)

FIGURE F.17 – HEAT SINK TEST POINTS

ANODE

CATHODE

	SW1	R2
+	V	R1
			SW2
6 VOLT	A		R1 = 4 ohms/10 watts
		G	R2 = 3 ohms/10 watts
LANTERN	SCR
BATTERY
	UNDER	C
	TEST

To test SCRs construct the circuit outlined above. Resistor values are plus or minus ten precent. The voltmeter scale should be low, approximately 0-5 or 0-10 volts DC.

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4.Construct the circuit shown in Figure F.17. One 6-volt lantern battery can be used. Set the voltmeter scale low, at approximately 0- 5 volts or 0-10 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 bat- tery.

5.Connect the Tester to SCR 1 as shown in Figure F.17.

a.Connect Tester lead (A) to the anode.

b.Connect Tester lead (C) to the cathode.

c.Connect Tester lead (G) to the gate.

6.Close switch SW-1.

NOTE: Switch SW-2 should be open.

7.Read the meter for zero voltage.

a.If the voltage reading is higher than zero, the SCR is shorted.

8.Close or keep closed switch SW-1.

9.Close switch SW-2 for 2 seconds and release and read the meter.

a.If the voltage is 3-6 volts while the switch is closed and after the switch is open, the SCR is functioning.

b.If the voltage is 3-6 volts only when the switch is closed or there is no voltage when the switch is closed, the SCR is defective.

NOTE: Be sure the battery is functioning properly. A low battery can affect the results of the test. Repeat the battery test procedure in Step 4 if needed.

10.Open switch SW-1.

11.Reconnect the Tester leads. See Figure F.17.

a.Connect Tester lead (A) to the cathode.

b.Connect Tester lead (C) to the anode.

c.Disconnect Test lead (G) from the gate.

12.Close switch SW-1.

13.Read the meter for zero voltage.

a.If the voltage is zero, the SCR is func- tioning.

b.If the voltage is higher than zero, the SCR is shorted.

14.Perform the Active Test Procedure outlined in Steps 5-13 for SCRs 2-6.

15.Replace all SCR assemblies that do not pass the above tests.

16.Plug J9 onto the thermal fan/snubber board and plug J5 into the firing board.

IDEALARC DC-655