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From: sb@pro-generic.cts.com (Stephen Brown)
Newsgroups: comp.sys.apple
Subject: Re: Weird monitor problem
Message-ID: <8906220856.AA13194@crash.cts.com>
Date: 22 Jun 89 05:59:55 GMT
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Network Comment: to #2587 by pnet01!crash!purdue.edu!mailrus!ulowell!m2c!wpi!dseah

For about the first 6 months, my monitor did exactly the same thing. It would
be on for a while and all would be well. Then after an hour it would whine
annoyingly until (a) it was given a few good whacks, or (b) until it felt
better, or (c) until the relative positions of the planets pleased it again.
Then all would be well again.

I WAS going to take it in to my local (?) freindly (?) Apple dealer, but the
problem went away by itself.  I suspect that it was either the PC-board, the
flyback transformer core, or the horizontal output transistor that was
vibrating in response to the 15,750hz horizontal-oscillator signal which
causes the electron beam to do a horizontal dance across the picture tube
screen.  

In TV sets, the actual offending vibrating piece may be difficult to pinpoint,
but its in there somewhere. I don't know whether the heat (and thermal
expansion) causes something to be the right shape/size to resonate, but it
would make sense.  Unfortunately, hard to trace, and the act of moving the
monitor might be enough to cure it.... I don't know.

Stephen Brown
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