Been working on my Bally Power Play game. When I got it it had a battery acid damaged original Bally -17 MPU. Thanks to Andrew over at barakandl I installed a modern MPU and the game is running great.

Flashback 25 years ago. Tom Callahan reached out and asked me if I would trial a new MPU he was working on called the Mutha Board. I was flattered and agreed to install one in my home Paragon game. Serial #4 came with Paragon Proms and worked as well as the original, later I used it in my sadly missed Fathom game where Mutha performed equally well as the original.

Yada Yada, 25+ years go by and I was clearing out of a storage locker I had been using, in a box labeled 'pinball parts' I came across Mutha board #4. I thought it would be a great tribute to Tom to put the board back in service. I also love old things that still work, like me. There was some modest battery leakage but only the battery holder was affected. I contacted Clive over at Coinop Cauldron and he sent me a set of proms. I also removed the batteries and added an NVRAM.
To my pleasant surprise the board booted and the game played nominally. The boards test LEDs had failed and no longer functioned but otherwise the game played great freeing up my B&I board for other projects.

This brings me to today, a few weeks ago the Mutha board failed. I noted an issue with the switch matrix where the switch in the row above would register at the same time. Roll over Switch 36 and 35 will show closed. This occurred across the entire row. I assumed that I2 and I3 of the matrix were shorted so I went through all the usual troubleshooting methods. After tearing up the cables I finally reinstalled the B&I board and the game worked fine. Whatever the problem was it was on the Muthaboard. I swapped PIAs, examined for shorts and nothing worked. Putting on my engineers cap again I decided the problem had to be with a bad input cap so I replaced the 330 pf input caps on the affected 'I' lines which fixed the switch problems. While I was at it I replaced the LEDs and now have working test indicators.

Which brings me to today. After replacing the caps a new problem, I was only getting 5 flashes which indicates a problem with the display interrupt. Sure enough a logic probe showed the DIG was locked on. I ohmed out the resistors and replaced the .1uf poly cap. The cap fixed the the DIG and now the board boots.
But now the displays come up flickering. That's usually a sign of a malfunctioning DIG. I replaced the cap again and put in a new 36K resistor and replaced the 555, but same result, flashing flickering displays.

Lots of smart people hear what do you think?
Pictures of Mutha below but my camera cannot properly capture the flashing displays.
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I will replace the noted caps and look closer at the blanking circuit. The game does go through the HSTD blank sequence properly so I'm skeptical that the blanking is the problem but I'm running out of things to check. Unfortunately, I have no way to measure frequency so I'm limited to making a judgement call to replace caps. Resistors are ohming out correctly.

I'm doing kitchen table repairs so it's possible I stressed some capacitors while laying the board down on the table to solder. C17 and C18 look like candidates to repair.

I have the B&I MPU in it now. It runs fine. Power Play is a -17 MPU all 6-digit displays
I replaced R21 with a new 36K 1% that I confirmed with my meter, same issue.
With original C16 555 was locked high. Replacing C16 with a new cap got the 555 running again and got my board booting past 5 flashes. Now It boots and runs fine but the displays are flashing. Reinstalling Andrews B&I board and the game runs nominally. So problem is definitely with the Muthaboard.

Update, finally fixed Mutha. I had tried replacing about all suspect parts to no avail. Then I backtracked. Capacitors C31-40 were supposed to be 390PF per the MPU schematic. On Tom's board, which is supposed to be a near exact reproduction, he used 470pf caps. Thinking it was an early mistake I outguessed his logic and replaced with the proper 390pf caps. Changing them back to Toms value of 470 fixed the problem. Go figure. must have something to do with how the 6802 scans the matrix.

Now I'm using the Mutha in my Skateball game I am restoring. Trying to understand how switches 1-5 and 9-13 are wired. I remember Tom telling me that he hardwired them to save on dip switches but I can't remember. Anyone out there have support documentation for this board that they are willing to share?

Thanks for all the past help.

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Wow thanks @quench! You wouldn't have a schematic would you? I'm intrigued about the freeplay relay. My original from 97 doesn't have that, or at least I think it doesn't.

So now I have another problem, I cant advance beyond self-test to set replays and game features. See this thread: https://pinside.com/pinball/forum/topic/bally-mutha-board-made-by-the-repair-connection-6802#post-8010458

Started doing this after I set a high score. I think I can fix it if there was a way to clear the memory settings. However with NVRAM installed I don't see a way to do that.

Of course, being a semi-retired senior citizen I have none of that equipment. I suppose I could get Clive over at COC to make this chip, but at this point I'm thinking it's no longer worth the effort or expense. What if I put my Power Play Roms back in??? I may be able to erase the scores from inside there. I'll try that, then it's time to admit I tried, throw in the towel, and order up a new Weebly BnI board.

Quench , This worked! With Power Play Roms installed I was able to get the game up and advance into bookkeeping setting. From inside there I advanced through and reset everything back to 0. Then I reinstalled Skateball Proms and was able to advance into the audit settings and set my replay score thresholds, and sound options.