I have a Stern Stars that I am having display issues with. What it does: When powered on, it boots up properly, with the proper flashes, then goes into attract mode. I can then coin up and play a full game with no issues. The problem is I have no displays. I discovered earlier today that if I complete the test switch circuit, the displays come on. SO, I turned the machine off, jumped the test switch, and the game came up normally, attract mode, coined up, played a game, but now the displays are on. What has been done to this point: the displays are all brand new Uno boards from Pinitech, the rectifier board has been rebuilt. SO, with all low voltage displays, F2 fuse has been removed as high voltage is no longer needed. The battery looks ok, but tomorrow, I am going to remove it altogether.....it will later be replaced with NVRAM. Any ideas? Thanks.

It's the original MPU. When I got it, the wires had been cut off of the test switch.....the switch itself is bad. I unplugged the J3 connector and the game booted up fine, just no displays. I will try swapping the chips to see if I get anything different. I have a friend that likely has a couple extra MPUs, but from different games. I may put one of those in place just to see if the displays works with a different board. So, question......if i get something different with a different board, can I swap the U10/U11 chips from that board, or are those game specific?

Update: I swapped U10 and U11 and it wouldn't boot up.....I only got 1 flash on the MPU and it was very weak. In looking at the chips as I removed/swapped them, 10 looked like a new chip and 11 looked like an old chip. So is U11 my problem? Thanks.

Fixed: both PIA chips were bad. Not sure how I was getting good flashes on the MPU, but regardless, replaced both PIAs and all is well! Thank you all for the help!