On Fri, 6 Nov 1998, Steven Keller wrote:

> Is it possible for an EPROM (16C63) to check out as blank, program, and
> verify correctly but not be fully erased?

Yes. I let them sun themselves one hour every 5 to 10 erase/program cycles
to avoid it. When I did not do that I did see strange things after a few
cycles (no pattern). I used 54JW, 711JW and 508JW. By the time I moved to
711 and 508 I already used my one hour sunbath method and never saw
strange effects again.

I suppose that an incmoplete erasure leves some charges that can migrate
back and forth after a while. I have also designed & built my own 54
programmer and wrote the soft for it so I did a lot of checking on erase
patterns, what is erased first etc. There is almost no pattern, you can't
guarantee that the fuses are erased last (on a 54JW), and in general, just
leave them in there long enough ;(

Peter