I checked the big transistor that was on the heat sink and it looks
fine. I took it out to test it, and also I checked in-circuit and
there are 130V across B-C and E-C while running (so I guess it's an
npn). There is also a capacitor with 20V on it and a capacitor with
130V on it.

Post a link to pictures of the unit. Check for an open (power)
resistor somewhere in the feedback loop.