Not to call victory too early but I think I found the problem…
So, I was going about trying what
@techknight suggested about poking at the board while it’s running. So, I took the front display bezel off and turned it on to find that as soon as the display finished initializing (the initial white screen went away, aka the computer took over control), it instantly went dark gray. I decided to mess with the voltage pots. Upon adjusting the pot labeled “V7”, it went away. I found that shorting any part of the pot to ground caused the display to go all gray again. The legs on it are a bit corroded so it’s probably a bad connection. For now, I’ve had it on for several minutes and the display looks perfect. If the issue comes back I’ll try to remove, clean under, and resolder the V7 pot, but it’s good for now!
Why don’t you give that a go
@mattia1071 and see if it fixes your issue!
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Edit: I've had it on for around 20 minutes now and there's no sign of the issue! I think this one may be fixed!