Hey NM,

I just went through this with my TZ like 2 days ago! Strange how these things run in cycles. Anyway before I did anything I checked the 5v to computer, with both flippers pressed it dipped down to like 4.6v and even less. It was intermittent, but happened every time once the game warmed up. I also checked the voltage out of C5 and BR2. You can do this with a meter which I highly recommend before replacing. Also I went through the transformer connections and the connections to the driver board.

Here is a good debug guide:
http://www.pinwiki.com/wiki/index.php?title=Williams_WPC#Game_resets

So I know my C5 was bad from my tests, I replaced that and went ahead and replaced BR2 (cost me $30.00 in parts). Problem solved.

I've now got a strange hum from the speakers (faint but you can hear it and I know I did not have that before). I'm thinking this could be the power transistor on the driver board or caps on the sound card but I'll have to tackle that on another day.

Good luck!

For repair's I personally feel spending the extra time to fix it with the original spec'ed parts are ideal. I've found the Williams and Bally engineering in the DMD era machines are solid, and with parts still accessible it makes me feel better about the repair. I've repaired a lot of machines this way and I've not had to go back and repair it again
Hope you find your problem.