Have you tried a completely separate 12v supply, like a wall wart, plugged into the service outlet, to power the inverter? Sounds like the inverter might be backfeeding noise onto the 12v line which would more than likely effect the optos.

I'm glad the adapter idea worked. I'm wondering if it would still work if you plugged the adapter into the service outlet and not the wall. I would think it should still work.

You can always wire an opto relay to power up the AC adapter when the game is turned on. If I were to get a Tron Pro someday, I would probably run a separate inverter for each color, have an opto relay on each AC adapter that powers each color, and have each relay triggered by some insert lamp on the playfield, like the light cycle insert for each ramp entrance. Not sure if those flash or not so it might be a little distracting.

Looks great though! Make me want a Tron Pro now! (was never a big fan of the light tubes on the LE - call me crazy)