Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 124

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ABNORMAL OPEN CIRCUIT VOLTAGE - AC 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 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
CH1
0 volts
2ms
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