On Friday, August 17, 2012 11:05:29 AM UTC-7, Slater wrote:

Is it possible to damage an EPROM by exposing it to UV light
for too long? What if a portion of the EPROM stays unprogrammed
('FF') and the chip goes through some program-erase cycles?
The unprogrammed area should fail sooner or later, shouldn't it?

I used only sunlight (Phoenix, AZ, 32N latitute, sky probably 90% clear), and for EPROMS written with all 0s, over 90% of the bits would erase in a day, 100% in 2 days, so I'd erase for 3-5 days. One summer I left a couple of EPROMs outside for a couple of months straight, and they all worked when I wrote all 0s to them, and the programming didn't take longer than for my other EPROMs, according to the programming method described in a TI data book, where a short programming pulse was used while the normal 5V supply went to 6V and the byte was tested after each write.