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F-33

TROUBLESHOOTING AND REPAIR

F-33

ABNORMAL OUTPUT VOLTAGE WAVEFORM - MACHINE LOADED ONE OUTPUT SCR NOT FUNCTIONING

0 VOLTS

20.0 V

5 ms

 

MACHINE LOADED TO 220 AMPS AT 22 VDC

 

 

SCOPE SETTINGS

 

 

 

 

This is NOT a typical DC output voltage

 

 

waveform. One output SCR is not function-

Volts/Div

20 V/Div

ing. Note the increased ripple content. One

 

 

SCR gate was disconnected to simulate an

Horizontal Sweep

5 ms/Div

open or non-functioning output SCR. Each

 

 

vertical division represents 20 volts and

Coupling

. . . . DC

each horizontal division represents 5 mil-

 

 

liseconds in time. The machine was loaded

Trigger

. Internal

with a resistance grid bank.

 

 

NOTE: Scope probes connected at machine

 

 

output terminals: (+) probe to electrode, (-)

 

 

probe to work.

 

 

 

 

 

POWER MIG 255C

Page 73
Image 73
Lincoln Electric SVM170-A service manual Machine Loaded to 220 Amps AT 22 VDC Scope Settings