Lincoln Electric SVM118-A service manual Abnormal Open Circuit Voltage AC TIG Mode

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F-65 F-65

TROUBLESHOOTING & REPAIR

ABNORMAL OPEN CIRCUIT VOLTAGE – AC TIG MODE

ONE OUTPUT SCR NOT FUNCTIONING

CAUTION

HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.

•Perform all voltage and waveform checks with high frequency circuit OFF.

CH1

0 volts

50 volts 2 ms

This is NOT the typical AC output voltage waveform. One output SCR is not functioning. Note the “gap” in the waveform. One SCR gate was disconnected to simulate an open or non-functioning output SCR. Each vertical division represents 50 volts and each horizontal division repre- sents 2 milliseconds in time.

Note: Scope probes connected at

machine output terminals: (+) probe to electrode terminal, (-) probe to work terminal.

SCOPE SETTINGS

Volts/Div	50V/Div.
Horizontal Sweep	2 ms/Div.
Coupling	DC
Trigger	Internal

SQUARE WAVE TIG 355