Bally Black Jack (Bally, 1978) problem with score count

[Pantaloon]

Hi,

I'm at the last stage of repairing my Bally Black Jack, but I've stumbled upon a problem I can't wrap my head around. Everything seems to work fine, but when playing the scores aren't added in a linear way.
The scores go up to about 58.000 like normal, but then immediately drop down to 24.000. When, after that, 40.000 is about to be reached again, the score goes back up to 60.000 and proceeds linear from then on. The same thing happens at 158.000. It happens a few more times as well, for smaller numbers.
It does this on all displays, no matter how many people are playing.
Has anyone had experience with this kind of malfunction or any idea what could be causing it?

Thanks in advance,
Pantaloon

 

[pinballdaveh]

many possible problems, cpu battery leaking or faulty,corrosion on the cpu board from leakage, faulty ic sockets, eproms not working properly,or rectifier/fuse board has corroded connections. if you cant check these yourself send the cpu to a expert for repair or evaluation,or replace cpu with the newer version.

 

[spalmer]

Sounds like a problem with U11 on the MPU board. U11 controls the score displays Try reseating it. Another thing that you can try is to switch U11 and U10 on the MPU baord and see if anything changes. BOth of these chips are interchangable. I have several machines with that same board. If needed, PM me. I would be willing to take a look at the board for you if you are willing to ship it.