Picked this 75amp up for cheap. Not alot of use, everything is very clean. It did weld when I first got it home but not well. The wire speed is all over the place. It 'stuttered' alot when you pull the trigger. Meaning the wire speed would stop-start-stop-start run steady for a short while then stop-start-stop-start. Same symptoms all through the range of the wire speed dial, a little worse mid-range. Settings 1-3 and 8-10 would allow longer constant speed run time Settings 4-7 had more stuttering. The Gas Valve pulled in as it should. I checked the liner & tip, changed wire. I went as ar as to remove the wire from the drive wheel and pull the trigger, the 'stuttering' continued.
I don't have a variable DC power supply so I removed the Speed Control from the circuit and connected the black wire to the rectifier where the speed controller's white wire is. The motor does not turn with 28VDC hitting it. Doesn't even get warm. I expected it to go full speed. Right? This tells me the motor is now dead?
I have been playing with the speed controller too but thats a different thread.
While I was troubleshooting this I ran into something I don't understand.
Why does the common wire from the speed control/drive motor terminate down stream of the rectifier and not to the same terminal as the common for the Gas valve? This is how the unit is wired.
Side Note: Double check me but I think the lower diagram doesn't match the top diagram.
Here's the diagram.