Re: burned and crashy

["Roger Johnstone" <rojaws@mac.com>]

In article <r7IB7.29107$6y3.1354522@sjcpnn01.usenetserver.com>, 
warnken@mother.com wrote:

> I checked this ROM3 system out before I installed the cards.
> It ran fine.  I added a TWGS (upgraded to 12.5MHz), Ramfast,
> 4 meg RAM card.  I ran this setup for a while and it was stable.
> One day I turned it on and went downstairs to do something.  I
> came back about 20 minutes later to smell something acrid
> coming from the machine. There wasn't any smoke. just bad smell.
> I looked and couldn't locate a place that the smell was coming
> from, though it seemed to be in the middle of the cards rather
> than the outside slots.
>
> The cpu system tests good, the TWGS self test is good, the Ram
> card tests good.  I put a different Ramfast in.  I added a
> Floptical drive and a IOMEGA drive.  It boots from either to
> system 6.0.1, but is unstable. I added the high density
> controller card and drive.  It'll boot from that too, but
> is unstable.  I've booted from system 5x on the 3.5" drive.
> It's unstable.  Sometimes it crashes before it finishes booting.
> Sometimes I can do something with it before it crashes.  Any
> suggestion where to look?  Or is it easier to get another cpu
> and start over.
>
> Sandy

Something very similar happened to my IIgs a few years ago, fortunately I
was there to see it happen though. A tiny surface mount chip capacitor on
the _underside_ of the motherboard shorted and burnt up.

It started with a tiny stream of smoke coming from the top of my IIgs, I
immediately turned it off and opened it up. Close examination of the board
and the cards revealed no obvious source of the smoke, so I left the cards
out and turned it back on, with the top off of course. Immediately I could
see, through one of the holes the motherboard has in front of each slot, a
disturbingly bright orange glow reflecting off the shiny metal base pan! The
capacitor was a bypass from the +5V rail to ground, it had shorted and the
power supply was doing its best to clear the short by burning a hole through
my motherboard!

Fortunately no major damage was done, once I dug out the remains of the
capacitor and some of the charred board everything worked fine. It's missing
a bypass capacitor on slot 4 but since nothing's in that slot it doesn't
cause a problem. If a bypass/filter capacitor has gone on a slot that is in
use or in an important part of the board it could easily cause stability
problems.

Sandy, I suggest you remove the motherboard and have a look at the
underside. Fortunately the IIgs is very well designed, you can remove the
motherboard in about a minute with no tools.

--
Roger Johnstone, Invercargill, New Zealand

Apple II - Future Cop:LAPD - iMac Voodoo2 - Warcraft II
http://homepage.mac.com/rojaws
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As a computer, I find your faith in technology amusing