Today while working on the rack closet the welder died on me for no apparent reason. But, after power off it made a couple of noises and the fan ran for a moment.
For being a Chinese machine it actually looks quite good and neat on the inside. The boards have conformal coating and just a tad of flux residue on some pads. The only thing out of place was a blob of solder on a header instead of a jumper.
I made a couple of measurements, the high voltage section was fine but the control supply was totally dead, except for a brief moment when turning off the main switch. Traced back from that board until finding a small block with a forward converter (kinda odd, I expected a flyback). The only component with bad readings was the recovery diode. I swapped in an UF4007 and at the next flick it was alive again.
Of all the things that could go wrong with a welder on novice hands this was not expected.