Canox Starpower / Miller XMT 300 welder: troubleshooting and repair

Troubleshooting and repairing this MIG welder for the second time, after a few months of commercial usage.
First repair was "easy", but this time there was much more damage.

I also go into a bit of detail on how these work internally and how I went about rigging it for lower power, safe(r) testing.

Audio quality is again appalling. Someday I'll learn how to record properly... maybe...

00:00 intro
02:07 initial probing, bridge rectifier + IGBT modules
04:23 suspicious IGBT
05:27 checking main PCB zeners
07:51 removed zeners
09:20 welder "theory of operation", partial schematics
24:47 testing film capacitor leakage
25:14 testing resonant tank
25:52 measuring main bulk capacitor ESR and ripple
26:15 testing gate drive signal and IGBT at low power
27:32 "Arc control" knob explanation
28:59 Closer look at the main PCB
33:07 final testing at 600V