Lincoln Electric SVM136-A service manual Figure F.16 SCR Tester Circuit and SCR Connections

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F-27 F-27

TROUBLESHOOTING & REPAIR

ACTIVE SCR TEST (continued)

FIGURE F.16 – SCR TESTER CIRCUIT AND SCR CONNECTIONS

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9.Construct the circuit shown in Figure F.16. One 6-volt lantern battery can be used., Set voltmeter scale low, at approximately 0-5 volts or 0-10 volts.

10.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.

11.Connect the tester to the SCR 1 as shown in Figure F.16.

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

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

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

12.Close switch SW-1.

NOTE: Switch SW-2 should be open.

13.Read meter for zero voltage.

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

14.Close or keep closed switch SW-1.

15.Close switch SW-2 for 2 seconds. Release and read 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 if there is no voltage when the switch is closed, the SCR is defective.

NOTE: Be sure the battery is function- ing properly. A low battery can affect the results of the test. Repeat Battery Test Procedure in Step 10 if needed.

16.Open switch SW-1.

17.Reconnect the tester leads. See Figure F.16.

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

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

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

18.Close switch SW-1.

19.Read 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.

20.Perform the Active Test Procedure outlined in Steps 11-19 for SCRs 2 and 3.

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

22.Replace all molex plugs onto the control board and snubber board. Reconnect posi- tive capacitor lead and small lead terminal.

23.Reconnect lead #204 to resistor R2.

IDEALARC CV-400