Bruce,
Bit further on this, FWIW, my first shotgun repair attempt (simply replacing the IGBT's), lasted about 5 seconds before blowing up, since I did not check that I had pwm drive, before enabling the HV (SMPS-101 lessons here)
I bit the bullet, and read up to understand how inverters/SMPS work. Poking around I found that GDT had shorted/opened I don't remember.
Replacing that transformer brought back the PWM, and the thing started working again, with new transistors
The welder is/was quite advanced for a early 90's design, with a very high duty cycle. Specifically stated 8KVA generator minimum, my bad..
The "6KVA" chinese honda that did the damage, essentially almost stalled at that time...
anyway, I don't qualify for even 2nd group above, ha...
nick