Lincoln Electric PRECISION TIG 185 SVM169-A Service Manual page 75

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.
____________________________________________________________________
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.
TROUBLESHOOTING & REPAIR
ONE OUTPUT SCR NOT FUNCTIONING
CAUTION
50 V
PRECISION TIG 185
2 ms
SCOPE SETTINGS
Volts/Div. ...............................50 V/Div.
Horizontal Sweep .................2 ms/Div.
Coupling .........................................DC
Trigger .....................................Internal
F-37
0 V