Re: Monitor Discharging

OK, I've read the entire thread now and it's time for my 2 cents worth.

For quite a few reasons, the discharge path must be to the outer surface (the
aquadag coating) of the tube. Since this is connected to the metal monitor
chassis, THAT'S where you discharge to, the chassis.

When you have a high voltage breaking down an air gap to form an arc you end
up with a brief high current with a very fast risetime. Due to inductance in
any wiring this current passes through you will have a momentary voltage drop
in the wiring. And the high current pulse will generate a magnetic field that
will induce this pulse into any close conductors. This is a very small-scale
and very localized version of the EMP pulses generated by nuclear bombs.

If you are discharging back to the power cord ground you will have quite a bit
of inductance in the return path and will briefly drop several hundred volts
across what you would normally think of as a low resistance path. This will
also induce surge currents into other lines along the path. The risk of
damaging solid-state electronics via this practice is unacceptably high. And
that assumes that you don't have a bad connection somewhere that would make
the pulses even worse.

The moral? Discharge ONLY to the immediate ground point of the CRT, the
monitor chassis itself. You could discharge to the aquadag coating, but the
chassis is safer since it connects to a larger area of the coating. Arcing
directly to the coating could damage it.

saint wrote:

> I had understood, and I am uncertain if this applies equally to vector and
> raster monitors (meaning I hope I'm on topic! :) ) that when discharging a
> monitor quickly, you go from annode to monitor chassis. I believe in fact
> someone was quite adamant that you *not* go from annode to a ground in the
> wall.
>
> I ran across this site that takes completely the opposite point of view:
> http://www3.50megs.com/todd1814/capkit/capkit.htm
>
> It also goes on that discharging to the chassis is a good way to fry your
> PCB.
>
> Anyone in the know care to comment? Is this web site correct, or grossly
> in error?
>
> Thanks!
>
> --- saint

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