Help With A MIG Welder That Stopped Working

Thread Starter


Joined Mar 16, 2021
I'm trying to help someone get an old MIG welder working. He used it a month ago and it worked properly. He went to use it a couple days ago and it doesn't work. When the power switch is turned on the cooling fan runs but there is no power to the solid state relay that controls the transformer the gas solenoid or the wire feed motor. I went over all the connections inside the welder and they all look good. There is a transformer that supplies power to the circuit board its putting out 28 volts. I measured the voltage at both ends of the large capacitor and there is 30.8 volts DC. I'm assuming there is a problem with the board. The trigger is pulled on the welding lead the circuit board should send power to the gas solenoid the transformer relay and the feed motor but nothing happens. The cooling fan gets its power from the circuit board and it works. The unit runs off 220 volts AC.

I verified the wiring and the trigger switch are good right to the connector on the circuit board. There is what looks like a thermal safety switch above the fan and it is good. The transformer relay and the feed motor are controlled by potentiometers on the front of the welder and they both check out okay.

Any help would be greatly appreciated.
Thanks!! Terry
Some pics of the board:

The two orange wires connected with spade connectors at the lower left are power in from the transformer.





The grey and black wires with the pen marks below on the left of the connector go to the trigger.
The black and white wires that connect to the board with spade connectors are for the feed motor.
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