My Time Fantasy (WMS System 7) has been trouble-free for over 2 years now; original MPU with zero battery damage and no Scanbe sockets. I rebuilt the 40-pin interconnect and power supply in 2019. The game ROM is custom to support an added feature using a relay to turn on a UV light to react with a custom playfield, but even that was proven stable for an entire show weekend in March 2020. No issues then; game has been played a few hours/mo at home between Mar2020 and this past weekend.
So this weekend I turned it on and played some games, then left it on... after a while I noticed the displays were out. Power cycled and they came back but the game had lost its mind: scrambled info on displays, no attract mode, no audit mode, etc. Further investigation revealed the MPU diagnostic display digit saying either "0" or "gibberish" or nothing at all every time I turned on the game. Displays would rarely if ever even flicker, random sounds would play or lock, etc. Just a whole range of random haunted weirdness.
To cut my rambling down: I wondered if my custom ROM had flaked out so I put the original one back in, but the symptoms were little changed. If I removed the driver board, the MPU would appear to stably boot to the "Zero Digit blink" (which traditionally points fingers at the driver board)... but not *consistently*. Still, I swapped driver boards with another game which confirmed the driver board was NOT the issue.
Finally I realized the MPU had a socketed CPU chip and I just happened to have a spare 6808... swapped the spare chip in and everything went back to normal. Put the original one back in and the game freaks out.
So, Yay... BUT! Thus far in my pinball tech "career" of 7 years, every chip failure I've experienced has generally traced to a direct cause-effect relationship. I.e., something (mechanical or already-stressed electric part failure; boneheaded troubleshooting fallout, etc) happened that caused a cascading failure at the chip. I never had a chip - much less a 40-year proven CPU! - just "die while sitting".
Now I realize that nothing lasts forever, and maybe that 40-year-old CPU chip finally just somehow "wore out" (It was an AMI brand which I understand might have been on borrowed time anyway)... but part of me isn't willing to think this is actually fixed.
How often does old, proven, otherwise reliable silicon "just die"? FWIW I've inspected the boards and connectors and there truly isn't anything obvious lurking. But I'd like to be at ease!