Lincoln Electric PRECISION TIG SVM186-A Service Manual page 77

F-37
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 AND REPAIR
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
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 discon-
nected 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.....................50V/Div.
Horizontal Sweep .....2 ms/Div.
Coupling.............................DC
Trigger.........................Internal
PRECISION TIG® 225
2ms
Note that
F-37
50 volts
0 volts