Light corrosion cleaned off the board, some components replaced, NVRam added. Works on cold boot but "crashes" after a while of being on, and on subsequent boots the R/W line of the 6502 is stuck. IRQ line is pusling and reset line starts out low, then goes high on boot. Would I be safe to assume the 6502 is toast, or could something else be causing the R/W line to be stuck?

My Ni-Wumpf MPU doesn't have issues booting, and I've done lots of work to the game so it isn't a problem with the power supply, connectors not being repinned, etc.

My game doesnt have a reset board

Got it, I will take a look, I vaguely remember my board having it but it's been a while since I've looked at the back side. I just read that section you linked, and it says that the chance of it being because of the resistor is slim. If the pullup resistor doesn't fix it, what else would you suggest? Is the pullup resistor a 1/4w?

Alright I think that pullup resistor solved the boot issue! It seems like it's booting consistently. Test 20, the memory test says the 5101 is bad, I tried saving settings for default high score and it wouldn't save. I tried starting a game but after it started I heard a coil continuously firing and it wouldnt get past the part where it's supposed to kick the balls out. Switch test reports 62 (left warbase hole) and 73 (10pt switches) are stuck, I dont remember the ni-Wumpf MPU doing that but its been a while. Displays are also a bit flickery

Fixed switch issues, both were due to stuck switches on the playfield. The Ni-Wumpf MPU switch test didnt tell me they were stuck . Game starts and works fine from the cursory test I did.

Displays are still occasionally flickery on some digits, and NVRam isnt working. I tried swapping in the original RAM that I desoldered and it didn't work either. Pics attached of the socket I added for the RAM. I checked continuity for the various input pins, some of the output pins, and also made sure there werent 2 pads under the socket itself bridged together. Im gonna keep continuity checking the output data and address lines

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Swapped in a 5101 from a parts board that I had, and memory test shows 99 which means the 5101 is working. That NVRam module must be bad :/ Now onto the displays flickering...

Yeah the pulsating is there which I expect but occasionally random digits in the 2nd and 4th player will flicker. I think it's likely a problem with Z24 or Z25. I used my probe and nothing appears to be stuck but I think I would need to break out the scope to know for sure (the scope I have that I don't know how to use lol).

Diode check on Z24 and Z25 is good, tried piggybacking a 7404 from a parts board onto Z24 and nothing changed. I noticed that Z26 also feeds digit 1 info to displays 2 and 4. Did diode test on Z26 and red lead on ground, black lead on pin 13 gave me a reading of 0.31, compared to 0.9 on the rest of the pins and all pins of Z25. I dunno if that means it's bad though considering pin 13 isn't used on Z26, so that could explain the different reading.

2 steps forward 1 step back... MPU stopped booting again. IRQ line stuck high, R/W line stuck high, Reset pin goes low for split second then high on boot which is correct. Clock signal from pin 37 is pulsing. Sync line is stuck low.

Here's my board as it currently sits with corrosion cleaned up. Nothing damaged on the backside. I might consider that reset modification but this is just a backup for my Ni-Wumpf MPU so depending on how hard it is I might just forget it. When your board stopped booting did the clock signal get disruped too, or only the CPU output?

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I went with the coin cell battery because I think the NVRam legs messed up the socket I installed. It was way too easy to pull chips out of the socket so I replaced the socket and went with regular 5101 ram. That was why my game kept saying the 5101 was bad, the legs weren't making good contact in the socket.

I did replace a couple of the components you circled and it didn't help. I ordered one of those MCP-130s from GPE, I'm gonna do the reset modification as you suggested.

The reset modification appears to have fixed my board not booting, thanks! Still having issues with the digits on player 2 and 4 flickering. Looks like every digit besides the far left digit is doing it. I suspect Z24 because it is a 7404 associated with digit strobing that feeds all but one digit of players 2 and 4.

Finished the reset mod and it helped the game boot once, but then it froze up and now wont boot again. Reset line is pulsing, r/w and irq lines are stuck on the 6502. I noticed after leaving it on for a while the 6502 was getting quite warm, probably as warm as the RIOT chips (which I know normally run warm). Is this normal or not? Also when it was running the 2nd and 4th player digits were flickering again so I suspect Z24 but I'll have to get to that later.

Changed the crystal and it appears to boot consistently now. Changed Z24 to fix the digits and it didn't help...

The digits only flicker on this MPU, I have a Ni-Wumpf MPU and it doesn't do it. I will have to check out power and ground on Z24 but I don't see why it wouldnt be

I see there's a cap (C31) connected to pin 14 of Z24 I could try changing or looking at. I have a parts board I can use to get Z25 and the cap, but it was robbed of the RIOT chips. Highly doubt it's a RIOT chip issue though as if a RIOT chip was failing I think I would have other way more drastic and visible issues.

Ok wiggling J3 caused other segements and digits to bug out so it is actually J3. Musta happened from me plugging and unplugging the original MPU for testing. Thought I was done repinning this game!!

Edit: repinning J3 didnt fix it AAAAAAAAh

Some of the fingers had copper exposed so I retinned all J3 fingers with a tiny bit of solder, then continuity checked every trace going into and coming out of Z25, and all traces leading to J3 fingers. No change. Last thing I can think of before I shelve it is to repin J2 as well.

Repinning J2 seemed to fix the displays then after I had it on for about 5 minutes the board froze up and stopped booting consistently again

Edit: displays arent fixed, game still boots inconsisently. Tried replacing Z2 Z3, no change.
When it did boot I still saw the displays bug out. I gave it my best effort but board repair is my weakest area and System 80 boards arent exactly noob friendly. Im shelving this for now. Hopefully in 6 months or a year I can bump this thread if I make headway.