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From: gould@physics.usc.edu (Christopher Gould)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Monitor problem
Summary: It's your walls
Keywords: 60 Hz magnetic fields
Message-ID: <20478@usc.edu>
Date: 12 Oct 89 15:36:43 GMT
Expires: 12 Oct 89 15:36:43 GMT
References: <1954@cunixc.cc.columbia.edu>
Reply-To: gould@physics.usc.edu (Christopher Gould)
Followup-To: comp.sys.ibm.pc
Distribution: usa
Organization: University of Southern California, Los Angeles, CA
Lines: 27

In article <1954@cunixc.cc.columbia.edu>
stone@cunixb.cc.columbia.edu (Glenn Stone) writes:
	>Advice on this monitor problem would be appreciated.  The text
	>undulates back & forth.  It only sways a few mm, but it's
	>visually disturbing.  I tried swapping the monitor (IBM
	>enhanced color display) and also swapping the EGA card; it
	>still does it.  It's actually quite nauseating to watch.

Your problem is that the power lines carrying 60 Hz 120 V which run
inside of your walls, generate magnetic fields which are not negligible
when current is carried.  It's a sad fact of life these days that most
(dare I say all?) monitors are _not_ magnetically shielded.

The oscillation you are seeing is at the beat frequency between the 60 Hz
wall power and the vertical sweep frequency (which is nominally 60 Hz).
If you look carefully for awhile you should be able to see this beat
frequency change (and perhaps even reverse) since the lines are only
guaranteed to be 60 Hz _on_average_, and not instantaneously.

The solution is to simply move your machine to a different location so
that it is not so near to these current carrying wires in your wall.

Either that or rip up your walls and move the wires.
_________________

Christopher M. Gould - Univ of Southern Calif - Dept of Physics   (213)743-8521
Internet: gould@usc.edu    Bitnet: gould@uscvm    UUCP: uunet!usc!physics!gould