I’ve been able to revive some pretty ratty looking, assumed out of commission carts for most of my time gaming. A couple years back, attacked a Batman and Robin Genesia cart and Banjo-Tooie with some brasso, q-tips etc, and after a little work they played perfectly.
The other day I snagged a boxed Killer Instinct Gold for like 10 bucks. Looked in pretty good shape…of course it won’t boot for anything! I’ve only had this happen one other time with a Kirby Superstar Snes cart.
A Sonic 1 cart I bought used. I’m not sure I ever got it working. I tried to clean it up as best as I could, even tested continuity (was good), but still couldn’t make it work. Dumping it several times with a Retrode gave me a different file every time, so I don’t think it’s bit rot.
i picked up a genesis copy of road rash forever ago - ive tried alcohol, brasso and so much, it just never boots. not a big deal with the mega everdrive about, but still sucks.
Had a few that have needed mass cleaning (recently a copy of Duck Tales on Gameboy that had a BLACK PCB from what looked like a coca-cola spill), but nothing that’s refused to boot.
I have a copy of Batman on Famicom that simply wont run, as well as a copy of Final Lap Twin on PC Engine that refuses to start after any sort of cleaning. Not sure what the hell is up with either one of those.
I work about 10-12 hours a week working with my friend that owns a retro game store and I’ve cleaned and tested hundreds of games. I have had a couple I couldn’t get to work, most were ruined by having soda spilled all over them. However, Gauntlet 4 still drove me crazy because the copy was in mint condition and only booted up once. I could never get that game to work for some freakin reason.