Path: utzoo!mnetor!uunet!husc6!bloom-beacon!mit-eddie!uw-beaver!tektronix!reed!kamath
From: kamath@reed.UUCP (Sean Kamath)
Newsgroups: comp.sys.apple
Subject: Re: Cooling fans
Message-ID: <9004@reed.UUCP>
Date: 23 Apr 88 23:39:39 GMT
References: <2889@charon.unm.edu>
Reply-To: kamath@reed.UUCP (Sean Kamath)
Organization: Reed College, Portland OR
Lines: 30

In article <2889@charon.unm.edu> cs2531bn@unmc.UUCP (Lazlo Nibble) writes:
>Even with the top off and a 5" fan constantly blowing over the motherboard, I
>was getting erratic heat-related problems, like random characters popping up in
>Applewriter.  Having the thing in a top-off configuration for three years
>hasn't exactly kept the thing clean inside either.
>
>Lazlo Nibble (cs2531bn@charon.unm.edu)

I know that with three cards and no fan, I was getting the same thing.  Then
with a fan and five cards, if I left in on overnight, weird chars.  Except
that it was always '?''s.  Aha!  I said to myself, what does this mean?

It means you have a bad 74LS245 chip on the motherboard.  Also, if may be on
the 80 column card.  THis chip is a tri-state bus buffer, and when it get's
warm, it sometimes doesn't go high-Z, I guess.  In anycase, make sure you
have a TI chip there, not some singapore sling.  I have succesfully left my
//e on for days, six cards and all, with only this change, with out a
problem (yeah, I have a fan. I ain't stupid".

SO: Check those 74LS245s,just to the left of the 80column card hole.  SHould
be next to an 74S109 (*not LS109.  If it's a LS109, it shouldn't be working
*at all*).

Sean Kamath

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