Lincoln Electric SVM169-A service manual 50 V/Div

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F-37 TROUBLESHOOTING & REPAIR F-37

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.

•Perform High Frequency Disable Procedure.

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50 V

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

Note: Scope probes connected at machine

output terminals: (+) probe to electrode, (–) probe to work.

0 V

2 ms

SCOPE SETTINGS

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

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PRECISION TIG 185