Troubleshooting & repair – Lincoln Electric POWER MIG 255 SVM144-B User Manual
Page 71
POWER MIG 255
TROUBLESHOOTING & REPAIR
F-33
F-33
0 VOLTS
20.0 V
5 ms
MACHINE LOADED TO 220 AMPS AT 22 VDC
ABNORMAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED
ONE OUTPUT SCR NOT FUNCTIONING
This is NOT a typical DC output voltage
waveform. One output SCR is not function-
ing. Note the increased ripple content. One
SCR gate was disconnected to simulate an
open or non-functioning output SCR. Each
vertical division represents 20 volts and
each horizontal division represents 5 mil-
liseconds in time. The machine was loaded
with a resistance grid bank.
NOTE: Scope probes connected at machine
output terminals: (+) probe to electrode, (-)
probe to work.
Volts/Div . . . . . . . . . . . . . . . . . . 20 V/Div
Horizontal Sweep . . . . . . . . . . 5 ms/Div
Coupling . . . . . . . . . . . . . . . . . . . . . . DC
Trigger . . . . . . . . . . . . . . . . . . . . Internal
SCOPE SETTINGS