I'm working on an MPU on a Bally Speakeasy that's got me stumped. I've got everything working now but when I play a game, there are two switches (14 & 26) that when activated, it just keeps activating the switch, adding the points and never stops, even once the ball hits the trough switch. I checked the diodes and the cap on the switches and they are good. Just to make sure it was the board I swapped in an Altek MPU and everything worked fine.

In switch test, both switches act as they should and don't keep activating like they do during a game.

The connectors at J2 and J3 have been repinned. I also went over all the diodes and resistors off from J2 and they look good. I swapped U10 and U11 but that made no difference. I also swapped in a working 6800 at U9 but no change.

Any ideas what could be causing this?

If I unplug J2 once the game starts non-stop scoring, it keeps on going. I dug thru the switch area of the MPU and couldn't find any bad resistors, caps or diodes. All traces look good as well.

I don't have much in the way of test equipment. A DMM and logic probe is the best I've got. If the 555 timer was at fault, wouldn't more than just these 2 switches be causing issues?

Is there any chance the dip switch banks could cause any weird issues like this? The reason I ask is that I've set the dip switches to make the game 3 balls per play (dips 31 and 32 to Off). When I start a game, it will say 3 balls to play and as soon as a switch is hit, it will move to 2 balls to play. Then when the 1st ball drains, it will stay at 2 balls to play until the first switch is hit, then it will say 1 ball to play and when that second ball drains, it ends the game.

If I set the dips to 2 balls per play, it ends the game after 1 ball. So something is causing the MPU to think the game is over 1 ball short then what it's set to.

I probably should have mentioned that this is a Stern MPU-200 with (2) 2732 roms. With help from Schudel5 tonight, we determined that the second 5101 at U13 was causing the problem. The Bally code is supposed to ignore the chip at U13 on a MPU-200 but after removing it, the ball count worked properly and switches 14 and 26 are no longer causing the game to go into a never ending adding of points. Thanks!