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From: lpb@cbnewsi.ATT.COM (louis.p.barbuscio)
Newsgroups: comp.periphs,comp.sys.ibm.pc
Subject: Re: Strange monitor problem (glow forming on monitor)
Message-ID: <1337@cbnewsi.ATT.COM>
Date: 1 Dec 89 15:36:23 GMT
References: <7592@cognos.UUCP>
Reply-To: lpb@cbnewsi.ATT.COM (louis.p.barbuscio,ho,)
Organization: AT&T Bell Laboratories
Lines: 37

It does sound like degausing would help.  Basically Cathode Ray Tubes
consist of an electron beam aimed at a phosphor screen and focused and
deflected by electro magnetic coils wrapped around the neck of the
tube.  All these magnetic fields sometimes have the effect of magnetizing
things in the vicinity of the screen which results in the kind of haloing
or shadowing you are experiencing. The way to get rid of this is simnply
to take a large coil of wire and connect some AC power to it and move it
around the screen like a divining rod (The coil is referred to as a degausing
coil and you can probably get a commercially made one from Radio Shack).
You might get the same affect by taking one of those plug/transformer
power adapters, like the ones used for battery adapters, plug it into
an extension cord and wave it around the screen.  The trick is to slowly
increase the distance between the screen and the coil.   Sudden movements
have the effect of leaving the spot magnetized.

Finally, it should be noted that most (if not all) modern Color TV's
and I suspect PC monitors have built in degausing coils that operate
every time the monitor is powered up.  It's a cheap circuit (2 turns
of wire around the face of the tube and a timed pulse of AC while the
power supply is getting up to speed.  Of course if you never turn the
monitor off it never operates.  Or it may be inoperative in your monitor.
You can check for the presence of a working built in degausing coil by 
doing the following:
    1: Take a small permanent magnet (the kind you use to stick things
       on your refigerator) put it against a spot near the edge of your
       PC screen.  You will notice that when you take it away a spot
       remains on the screen.

    2: Power down the monitor and turn it on again, if the monitor has
       its own degausing coil the spot will be gone.  If not, well it's
       time to find the AC adapter for your kids SONY Walkmen and start
       doing the degausing boogie.
_____________________________________________________________________________
Lou Barbuscio, AT&T Bell Labs, Holmdel NJ, lpb@cbnewsi 201-949-7687 
Disclaimer:                           |  "Happy the man whose mouth (or
After 34 years I'm not sure if I speak|   keyboard) brings him no grief "
for the company or it speaks for me.  |                 Sirach 14:1


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