Abnormal Open Circuit Voltage-Dc Tig Mode-One Output Scr Not Functioning - Lincoln Electric SQUARE WAVE SVM141-A Service Manual

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ABNORMAL OPEN CIRCUIT VOLTAGE - DC TIG MODE
HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.
• Perform all voltage and waveform checks with high frequency circuit OFF.
• Perform High Frequency Disable Procedure.
TROUBLESHOOTING & REPAIR
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
50 V
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 dis-
connected to simulate an open or non-
functioning output SCR.
each vertical division represents 50
volts and that each horizontal division
represents 2 milliseconds in time.
NOTE: Scope probes connected at
machine output terminals: (+) probe to
electrode, (–) probe to work.
SCOPE SETTINGS
Volts/Div....................50 V/Div.
Horizontal Sweep .....2 ms/Div.
Coupling.............................DC
Trigger.........................Internal
SQUARE WAVE TIG 275
0 V
2 ms
Note that
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