I'm putting this here for future reference, for when I forget or hopefully it will help somebody else out.

The other day I blew another driver board, I have no idea why, this one just went. It was an AMP-0029. I really didn't want to pay for it though there is a AMP-0034 on E-bay for $1311. I had an AMP-0040 that had blown several years ago that I was going to send out for repair, but never got around to.

I pulled the AMP-0029 and the AMP-0040 apart and started checking things. First thing I noticed was that the resistance from the B+ to the B- terminal on one board was 10 times higher than the good boards still in the machine, and that there was a dead short on the other board. The B+/B- runs through 6 transistors, Toshiba pn GTK45735. One board had 3 transistors with massive resistance, and the other board had two with a dead short. Simply put, took 2 good ones off of one board, and replaced the two with a dead short. Back up and running in a couple of hours.

Now I have no idea if this is a common problem, or if it would have worked on the board with the very high resistance, but it saved a bunch of money and downtime.

what company did you find the transistors? I have the same exact problem.

I had another board that was toasted on hand to scavenge from, Google your brains out, there were places selling them.

As a follow up, I quit that hell hole shortly after, I know they lost a board about 3 months later, I don't know if it was the same one though. I'm sure this isn't how they all go out, but free vs $1800, it was worth a shot and kept the machine going.