My Firepower has an issue where the Player 1-2 scoring works great, but Player 3-4 are very erratic, with scores jumping all over the place as you play. In Display Test, the Credits/Ball in Play and P1 and P2 displays all test fine, but P3 and P4 count up as 0-1-0-1-0-1-6-7-8-9, which appears to me as though either all 6 of the first digits are bad, or digits 2-5 are bad with the original 0-1 being correct. It's hard to know which at this point.

I've replaced the associated PIA and re-pinned all the MPU connectors with no change in behavior. The display system is a brand-new Rottendog, which the previous owner installed in an attempt to resolve this problem.

I'm leaning toward swapping out the 74154 decoder. Anyone ever seen this sort of behavior? Does that sound like a likely culprit?

Dave

OK, thanks. That will save me some work on swapping the decoder. The same issue existed with the original Williams Master Display board so I'm tending to think it's not the Rottendog. I guess I'll meter all the display connectors for continuity and re-pin those on the display-side with crimp replacements from Great Plains if I can get them. I also have a probe so I can check for the outputs and inputs too. There's no other connectors in the harness - it runs direct from the Master back to the MPU.

Well, no luck so far. The logic probe shows all 8 outputs at the PIA pulsing, with the 8 inputs on, I believe it was IC13, also pulsing. No way of telling what the data is with a probe, of course, but at least I don't believe there are any open connections. As I mentioned, all of the MPU connectors have been re-pinned with trifurcons and I have new connectors on the way from Great Plains for the BCD inputs to the Master Display board. I'm going to keep poking at this as I'd like to have a spare, good MPU and I can use the troubleshooting experience, but I'm also side-stepping the issue with a new MPU from Kohout.

Any other suggestions are welcome!

Dave

Closing the loop here for future forum searches- the issue was indeed with the 74154. I pulled it and replaced it with a cannibalized chip from a broken Alien Poker MPU. Bingo! Scoring is now working properly. Thanks for all the help and suggestions!

Yeah, I don't understand enough of that system to comprehend what does what, but beyond the PIA and the displays themselves there wasn't much else left. Had the 74154 not worked, I would have been down to swapping the connectors on the display side, since I had already rebuilt the MPU side.

I also ordered a new Kohout MPU for it, which I'll go ahead and use anyway, keeping this one as a spare.