Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 123

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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.
TROUBLESHOOTING AND REPAIR
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
50V
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
CH1
0 volts
2ms
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