Re: Monitor Discharging

On Thu, 9 Dec 1999 09:31:43 -0500 (EST), you 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!

He has no idea what he's talking about:

"Because discharging a monitor involves removing the electrons stored
in it, we need somewhere to put them."

You can stop reading after that sentence alone.

The CRT is simply acting like a capacitor. One side of the capacitor
is the metallic paint coating the inside of the tube. The other side
is the metallic paint coating the outside of the tube. The dielectric
is the glass.

The anode (where the cap is attached) is connected to the inside
coating, and the spring that runs across the CRT and then attached to
the chassis is how contact is made with the outside coating.

To discharge the tube you simply need to "short" the capacitor. Since
the spring across the CRT is attached directly to the chassis, the
best way to discharge the tube is to short the anode to the chassis.

Some HV units use a voltage divider from the anode to gnd, with a tap
that is used for the focus voltage. This would discharge the tube
within a few minutes of powering off. I don't remember which is
which, but I'm pretty sure the WG's do have the voltage divider. (But
don't take *my* word for it, discharge the tube!)

On a dry static day, a CRT just sitting on a bench can build up a
pretty decent charge, so be careful in those circumstances.

A CRT discharge hurts, but it won't kill you. (Unless you're wearing
a pace maker, or some type of heart monitoring device that allows a
low resistance path directly to the heart.)

There was a jock in my high school electronics class that would show
off by discharging picture tubes "through his body". Yup, he's
probably at home right now (twenty years later, beer in one hand),
saying to his wife:

"Remember when I used to discharge picture tubes through my body?
That was pretty funny huh?"

"Uh huh. Now do ya think you could pick up those dirty socks and take
them into the bedroom?"

-Zonn
Received on Thu Dec 9 13:04:54 1999