An Atari Lynx II that won’t load any games and shows INSERT GAME, fixed by cleaning the cartridge contacts and, crucially, the console’s cart slot.
A leaky Amiga A501 half meg expansion caught in time: battery removed, alkaline leak neutralised with vinegar, and a test with early 90s cover disk demos.
A 3DO FZ-1 bought as working had an intermittent fault. Leaking power stage capacitors were the cause, and replacing them exposed a failed regulator and blown fuse.
The smashed Mega CD works, but it looks awful. I strip it down, sand and polish the rust off the shielding, fix the bezel, rebuild it and play some discs.
A filthy PC Engine CoreGrafx PI-PD6 pad gets a full teardown, a soapy wash (no alcohol near the conductive pads), contact cleaner and careful reassembly.