Double check the three switches in the ball lock area are working consistently. May need adjusting.

I played one this weekend that did the same thing. I can't tell you how to fix it but i imagine shanetastic is right!

Mine has been occasionally doing this and I'm fighting it too. I've done a lot of searching on RGP and what most people report is switch #3 in the lock trough (the top one) getting triggered. When this happens the machine ejects all the balls. It could be getting triggered from misadjustment, a bad diode, or a short, etc. Other people report problems with the stand up targets at the ramp because they are in the same row and column as the lock switches. They take a beating and if a stand up is tweaked, bent, and causing a short, it can cause phantom switch triggers that eject the balls. Finally, look overall for shorts, solder splash, or gimpy wiring.

Every time I think I get mine fixed, the problem seems to eventually crop up again. I haven't been able to reproduce it consistently so I haven't been able to find the root cause of it. I hope to get a chance to dig into it again soon.

I had the same issue with mine, Shane and Stangbat are exactly right with their diagnosis. I spent over a month continually troubleshooting and adjusting these switches thinking I had it fixed only for the issue to show up again a few days later. I finally got fed up and just replaced all the switches and diodes and haven't had a problem since.

Hope you get it fixed!

Thanks for the update, soren. Mine has been acting fine lately but if it acts up again I'll have to double check the first switch and make sure it is not being opened and closed.