[sebhc] CRT flashover [was Good news, bad news -- Robin succeeds]

[Lee Hart]

From: "Barry Watzman" <Watzman at neo.rr.com>
>> Bottom line:  The problem was caused by arcing inside the CRT from
>> "crap" (could be microscopic, invisible crap) that was initially
>> present inside a new CRT.

Robin England wrote:
> My father ran a consumer electronics repair company for many years
> and they recognised it as the cause of problems when TV sets started
> to use digital ICs. Inexplicable problems where serial EEPROMs would
> suddenly lose configuration data etc... As far as I know the devices
> were not permanently damaged in those cases though.

Heath was actually rather brave (or ignorant) to put a computer in the
same box with a CRT, without any of the usual shielding around the CRT.
The CRT, flyback transformer, and associated high voltage wiring can
cause corona, arcing, and electric fields that wreck havoc on sensitive
circuitry.

I remember using EPROMs in my H89 without bothering to put a sticker
over the window. They mysteriously got erased. Running in the dark, I
could see the dim blue glow and hear the faint hiss of corona around the
flyback transformer, which is right next to the EPROMs. It turns out the
corona was producing ultraviolet light, which was slowly erasing the
EPROMs!

The disk drives were the most sensitive to CRT noise. 80-track
double-sided drives were the worst offenders. Heath finally came out
with the H88-9 kit to totally enclose the disk drive in a steel box,
which was carefully bypassed and grounded to keep CRT noise out of it.
-- 
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
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