Lincoln Electric SVM129-B Switch Board Test, Figure F.11 Switch Board Resistance Test

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F-34 F-34

TROUBLESHOOTING & REPAIR

SWITCH BOARD TEST (continued)

FIGURE F.11 - SWITCH BOARD RESISTANCE TEST

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TEST PROCEDURE

NOTE: There are two switch boards. One is located on each side of the machine.

NOTE: The switch boards are designed to receive gate (turn-on) signals from the driver board (pulse transformer secondaries). The internal board circuitry processes the signals and outputs them to the FETs. The switch board cir- cuitry contains snubber circuitry to protect the FETs. This protection is supplemented by off- board resistors. The switch board design accom- modates the connection point(s) for the capaci- tor(s), main transformer primary windings, input rectifier, and reconnect switches.

1.Turn off Invertec STT and disconnect main AC input power to the machine.

2.Using the 5/16" nut driver, remove the case wraparound cover.

3.Perform the Input Filter Capacitor

Discharge Procedure. See the Maintenance section.

WARNING

ELECTRIC SHOCK can kill.

•Before continuing with the test procedure, perform the capacitor discharge procedure to avoid electric shock.

4.Disconnect all wiring harness leads (401/403, 1/8, 9, 12, 4/5, 402/404) from the switch board.

5.Fold the leads up so they do not interfere with the exposed terminals. See Figure F.11.

6.Using an analog ohmmeter, perform the resis- tance tests detailed in Table F.5 and shown in Figure F.11. If any test fails, replace both switch boards. See the Switch Board Removal and Replacement procedure.

7.If the switch boards appear to be burned or overheated, or if the machine was supplied by a 380 VAC or higher voltage supply when the failure occurred, replace the capacitors and the switch boards.

INVERTEC STT