This is NOT the typical DC open circuit voltage
waveform. One output SCR is not functioning.
Note the “gap” in the waveform. One SCR gate
is disconnected to simulate an open or non-
functioning output SCR. Each vertical division
represents 20 volts and each horizontal division
represents 2 milliseconds in time.

Note: Scope probes connected at machine out-
put terminals: (+) probe to positive terminal, (-)
probe to negative high inductance terminal.

SCOPE SETTINGS

Volts/Div.....................20V/Div.
Horizontal Sweep.....2 ms/Div.
Coupling ............................DC
Trigger .........................Internal

ABNORMAL OPEN CIRCUIT VOLTAGE WAVEFORM

CONSTANT VOLTAGE MIG

ONE OUTPUT SCR NOT FUNCTIONING

0 volts

2 ms

20 volts