double and triple check your connectors. I believe there is a connector on the right side of the driver board where the power comes in. I had the IDC connections on that go bad, and it caused problems because the whole machine would lose its 5V. I finally discovered it when I had the Kahr board installed, and the sound reset, but the game was still running (MPU didn't lose its 5V). I had replaced all the caps, rectifiers, modded the board for higher 5V, etc. Came down to the simple IDC connectors that seemed good, but apparently were not. Just re-pin them if there are any questions about them...

Jeff