The "board" in Steve's welder is a real oddball
There is a 24V control transformer that powers part of it. This allows some functions. The motor speed control circuits and motor are actually powered by the main welder output---the same power that feeds the gun/ the weld
So with the welder powered on, the 24V transformer goes to a bridge rectifier on the board and provides control voltage. When you pull the trigger, the larger relay feeds 120V AC to the big main transformer, which comes alive, goes to the main welder rectifier, and provides unfiltered DC to the welding gun AND BACK TO THE BOARD to the speed control, then back out to the feed motor.
One problem with trying to decipher these things is that there seems to be a "number" of variations likely made by several/ many small manufacturers in "whatever third world" these come from. I did finally find a diagram "in Russian."
And of course I did not have the rest of the welder to troubleshoot it as a unit.
