Lincoln Electric SVM118-A service manual 50V/Div

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F-64 F-64

TROUBLESHOOTING & REPAIR

ABNORMAL OPEN CIRCUIT VOLTAGE – DC 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 DC (+) 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