This is crazy. Mine was intermittently throwing two balls just recently. When I pulled the glass, I ended up noticing the trough kicker was pretty slow (the shaft was pretty sticky and it just wouldn't return very fast). I went ahead a cleaned that kicker not really thinking it was a big issue. At the same time, I had done a bunch of stuff like cleaning all the optos all over the game, checking the trough switches in switch test, etc and now game seems to be working ok. Apparently as this thread seems to prove, that kicker has to get back down before the CPU kicks another ball. I've had optos that seemed crazy dirty but we're still working ok so this idea with the ball kicker is great knowledge. Great thread!