Ross: Toll exchange mention - may recall.

>> True, but light is known to have funny effects without necessarily
>> erasing the device, witness the problems people have with windowed PICs
>> when they do not cover the window.

> Remember that we're talking about eproms here, not pic chips.

We found, as Olin did, and no doubt many others, that light affected
EPROM operation. A misbehaving program could be corrected by placing
even a sheet of paper between the fluorescent lights and the EPROM
window. These were probably 2716 single supply, just possibly the
older triple supply ones but probably not. Also maybe 2758 (which in
at least some brands just a 2716 with the "bad" half found on test
switched out. (You could see the same die size and arrangement through
the window).

The international telephone exchange in Auckland NZ had a sign
prohibiting camera flashes after somebody caused an 'outage' by using
a flash. In that case it was caused by the effect on an optical sensor
on the tape drives used to log call data - possibly an EOT (end of
tape) sensor.

At one stage we erased EPROMS on a brick window ledge using sunlight.
Remarkably effective. But the mortality rate was noticeable. By adding
an aluminum plate under the EPROMS or by inserting them in conductive
foam the mortality rate dropped to zero. Nice warm sunny conditions on
a dry smooth brick surface is apparently not an ideal antistatic
environment :-).


                Russell




                       Russell
--=20
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