Spehro Pefhany wrote:
Unfortunately, EPROM data are not designed to last for 20 years. It's
amazing to have lasted so long already. My first bet is the EPROM
losing contents. Unless you have a copy of the data somewhere, forget
it.

Reducing the supply voltage a bit (was it? or increasing?) might still
recover the data.
Yes.

....also had good experience with carefully cooling
the EPROMS during readout...

Erik.