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From: rpw3@redwood.UUCP (Rob Warnock)
Newsgroups: net.rumor
Subject: Re: Strobe lights -> crashes
Message-ID: <195@redwood.UUCP>
Date: Sun, 31-Mar-85 07:18:07 EST
Article-I.D.: redwood.195
Posted: Sun Mar 31 07:18:07 1985
Date-Received: Thu, 4-Apr-85 05:45:33 EST
References: <1185@ihuxi.UUCP>
Distribution: net
Organization: [Consultant], Foster City, CA
Lines: 37

+---------------
| I have a repeatable example of photographic strobes causing a computer
| to crash... Every time the photographer took a picture nearby, the micro
| would go belly-up, and have to be reset. The closest thing it had to an
| optical sensor was its EPROMS, and these were not erased by the flash...
| 	Chris Scussel | AT&T Bell Labs
+---------------

The base-collector junctions of transistors tend to be light-sensitive (go
look at how they build "photo-transistors"). It has been long known (but not
always publicized) that the transistors in the sense amplifiers of certain
EPROMs are especially light sensitive. It's not the ROM cell that's affected,
so the data is not erased (unless there's enough U/V, as with naked sunlight),
but read errors can happen. That's why the "paper" labels that are supplied
on preprogrammed EPROMs often have an aluminum-foil layer in them, to block
out light. Higher-frequency ("blue"er) light affects the EPROMS worse; hence
flourescent light is worse than incandescent.

I have seen (*blush* -- and been bitten by) this effect in prototypes,
when engineers get busy and don't put labels over the little "windows"
after erasing them.  It starts getting late in the day, someone turns
on the lights, and BOOM! CRASH!

It can also cause EPROMs to appear bad when freshly programmed, since if
you don't cover the window while programming them, PROM blasters which
use "adaptive programming" can get read errors during the programming
process (due to overhead lights), or during the "verify" step.

Moral: Cover your EPROM windows with OPAQUE labels, except when erasing.


Rob Warnock
Systems Architecture Consultant

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