I've noticed on completion of a game the match number regularly ends with a one rather than a zero.
This does not stop the match from working though for example if my score ends with '90' and the match displays '91' it still pays a credit.
Now my original VFD score display showed this issue and I didn't bother much with it as I was planning on replacing the display.
I have now installed the RetroElectro Colour Classic displays and the problem still happens.
So I can rule out it being a display issue as the problem stayed when I swapped to a different VFD and when I installed my new displays.

I don't see how it could be a problem with the pins in the connector on the MPU else it would impact all displays not just the credit and match display.
It also can't be the D0 to D3 or blanking pin on the display plug else it would cause issues with the other digits on the credit display, likewise I don't think it can be the digit display pins.

Also when you first turn on the machine before a game is played it displays a zero in the ball count and some of the time it displays the match correctly with a zero in the right digit.

All I can think is there is something odd happening within the MPU, but I'm at a loss as to what that could be.
Does anyone else have an idea?
Below are a few photos showing '91' in the match when I had the VFDs installed, then a '31' on the match with my new display and it working correctly showing a '40' in the match.

Has anyone ever seen this before?

20230523_184656 (resized).jpg

20230523_185002 (resized).jpg

match 91 (resized).jpg

I pressed the reset button when setting the high scores for credits to get rid of the odd values in the RAM for that.
Do I also need to do that for the match?
If so how?

Repinning the digit enable connector for the display is worth I try, I will give that a go tomorrow.
If that doesn't work when my 1.5F supercap arrives and I remove the MPU from the machine to fit I will try removing U10, cleaning the pins and reseating it to see if that makes a difference.

Shame my Retro chip tester can't test 6820 chips, maybe its time I bit the bullet and bought myself a RIOT tester that also does these chips.

Yes my RTC can test the 5101, I do hope that is not the problem as mine was replaced at some point due to leaking battery damage, but was replaced with a lovely looking AMI purple ceramic and gold chip and I will be really sad if I have to replace it with a plastic one.

To test a 5101 RAM chip on my RCT you select chip 2101.
I tested it multiple times and it passed every time, so the problem is unlikely to be the RAM chip, unless its a weird timing issue, will try swapping around the 6820 chips and see what happens as I don't have anything that can test these chips yet.

5101 test 1 (resized).jpg

mpu (resized).jpg

Interesting, I have swapped around the PIAs and now I'm still getting a '1' in the zero position on the match, but now also sometimes having a '1' in the zero position on the score too. Will swap the PIAs back to the way they were and see if the issue goes away from the score.
If it does I'm going with a faulty PIA, if it doesn't its time to repin some more plugs

PXL_20230525_062751001 (resized).jpg

PXL_20230525_062815764 (resized).jpg

I swapped the PIAs back the original way around and so far have played 8 or 10 games and it has worked perfectly every time.
I won't yet call it solved, but it is looking like I might of just had bad contacts with the PIA in the socket and removing and reseating it a couple of times may of fixed it.

I'll update this again in a few more days if its still working correctly.
Thanks everyone for your help.