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From: briand@tekig4.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Is my mac about to fry?
Message-ID: <1579@tekig4.TEK.COM>
Date: Tue, 16-Jun-87 14:28:15 EDT
Article-I.D.: tekig4.1579
Posted: Tue Jun 16 14:28:15 1987
Date-Received: Thu, 18-Jun-87 04:08:19 EDT
References: <403@oswego.UUCP>
Reply-To: briand@tekig4.UUCP (Brian Diehm)
Distribution: na
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 46

>I use a Mac 512Ke with Apple HD20 at home and with the recent warm weather
>it has developed a high-frequency (15-20 khz) "whine" after it has been
>on for awhile.  It only seems to happen on warm (over 75 degree) days
>after the computer has heated up.
>
>I've read a lot about power supply failures and I'm wondering if this is
>a prelude to a breakdown (I remember having a b/w tv years ago that did
>this for awhile before the flyback transformer went up in smoke...).

This all depends upon how sensitive your ears are at 15.5kHz :-)

Very probably all that is happening is that expansion is allowing components
in the flyback transformer to vibrate sympathetically. I've seen Macs that are
noisy straight out of the box, I had one that only made a low whine after it
warmed up for 30 minutes, and most are pretty silent. I have never heard one
so loud it sent me out of the room, but I've heard them annoying enough to
cause people to hold conversations elsewhere.

The way I've fixed a few of these is to stick toothpicks into the frame of the
flyback transformer wherever vibrations might start. For example, there is
often a frame wire around the ferrite core material, to physically hold the
core together. Sticking a toothpick between the frame wire and the core ferrite
in a few places (breaking off the unneeded end) seems to fix these right up.
Apparently the wood, being a flexible material, can absorb these vibrations.
You don't need to jam these in super-tight: if you're worried about breaking
something don't do it.

Also, putting RTV Silastic around the same locations can dampen the vibrations.
This is the vaseline-like goop they use to conduct heat between transistors and
their heat sinks: it conducts heat but is highly dielectric.

I would warn you to unplug the Mac and completely discharge the high-voltage
section before doing any of this, or you may find a new meaning of the Mac
term "alert!" Also, though I think this is a good thing to try first, I won't
be held responsible if your board later burns up - it could be that this is
simply not the problem.

As for how much you're looking at to repair, call your dealer and ask how much
a standard video board replacement costs. If it's too much, you might consider
buying AppleCare before you need it. I believe, but I don't know, that the
dealer's cost for a video board swap kit is about $80 - can anyone correct me?

-- 
-Brian Diehm     (SDA - Standard Disclaimers Apply)
Tektronix, Inc.
briand@tekig4.TEK.COM   or  {decvax,cae780,uw-beaver}!tektronix!tekig4!briand