old(ish) computers for sale

Those are entirely too common, in my experience. The most bizarre thing I've seen along these lines, however, was the light-emitting EPROM. One day I noticed that: 1) My Apple ][ was acting somewhat flaky. 2) The 80-column video card, a Videx Videoterm, was getting rather warmer than usual. 3) There was light coming from the video card. I put the card on an extender, and determined that the source of light was the firmware EPROM! There was an arc between two of the bond wires. The EPROM was a 2708 EPROM, which you will recall used three power supplies, +5, +12, and -5V. Amazingly, the EPROM was still completely functional, as the 80-column card was working fine. But it was pulling the Apple's 12V supply down to about 8V, which was causing other things to flake out. I replaced the EPROM, and unfortunately I didn't think to save the arcing one. Just at a guess, I'd imagine that the spectra of light emitted by the arc probably included enough short-wave UV that the EPROM would eventually have erased itself.