I just spent a few hours bringing back a Bally MPU from battery damage hell. Worked through various issues, but is booting to six flashes on the bench. The game is not quite ready for the board set yet, but soon I will finish assembling everything.
I have a Stern 100 MPU that I have never been able to figure out, so I broke it out after my Bally repair. The LED is locked on. But, some things I do know is U9 is running (or trying to run) because I have traffic signals on my data and address lines, if I reset the U9 by grounding pin 40, the traffic signals stop. There is clocking for pins 3 & 37, but it is at a different rate than my Bally MPU.
The LED is high from the R107 pullup resistor. It never gets a low signal from U11 and the CA2 line.
I don't know the Stern board and if it is a 100% copy of the Bally? This board has U2 and U7. It doesn't appear that any other chips were in the U1 or U6 sockets (if you look at U10, you can see how the board color originally looked).
I'm wondering if the MPU clocking is off. Someone did some hacky repair around U15. I have not looked at this board yet with my scope, but wanted to run this past everyone while I find more time to look at this board.
I would just like to get this board to boot to the first or second flash. I would like to use it to test 6800s and basic tests on 6820s.