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From: myers@hpfcdj.HP.COM (Bob Myers)
Newsgroups: comp.sys.apple
Subject: Re: Weird monitor problem
Message-ID: <11270008@hpfcdj.HP.COM>
Date: 21 Jun 89 22:10:24 GMT
References: <2869@wpi.wpi.edu>
Organization: Hewlett Packard -- Fort Collins, CO
Lines: 36

>A friend of mine has taken to beating his Apple IIGS RGB monitor.  After about
>an hour of use, something inside it starts this incredibly annoying
>high-pitched whine.  Whacking the monitor will fix it for about ten minutes,
>but the noise soon returns.  After a certain point, nothing will stop the
>noise, and my friend has to poweroff for at least an hour.

>Any ideas what is causing this?

This is almost undoubtedly one of the magnetics in the horizontal deflection
circuit - probably the flyback transformer - vibrating at the horizontal
sweep frequency.  This sort of thing happens quite often, and usually
flybacks and the like are varnished, potted in epoxy, or otherwise secured
to prevent it (it's really the ferrite core vibrating in its mounting, or
the two halves of the core vibrating, etc.).  The horizontal linearity
coil is also a likely culprit.

You can confirm the problem by touching the flyback with an *insulated*
rod (a plastic rod is ideal, or touch it with the eraser end of a wooden
pencil), and listening for a change in the sound - or maybe even a cessation 
of the noise. (NOTE: The insides of monitors are dangerous places to be - there
are some particularly nasty voltages to be found here, esp. around the
deflection circuits and flyback.  DO NOT do this unless you're confident
you know what you're doing!!!!)

If you can confirm which part is "singing", try fastening it down a little
better by using some RTV adhesive or HV "corona dope".  (Whatever you use
should be suitable for high voltage and moderately high-temperature
environments.  I've used RTV with some success for quite a while.)  Pay
particular attention to the core mounting and any gaps between core pieces.

Hope this helps!


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
myers%hpfcla@hplabs.hp.com               |  sentient life-form on this planet.