Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!ames!uhccux!patten
From: patten@uhccux.uhcc.hawaii.edu (Brian Patten)
Newsgroups: comp.sys.mac.hardware
Subject: Dead Mac+ Logic Board
Summary: I found the bad chip. Now what?
Message-ID: <7101@uhccux.uhcc.hawaii.edu>
Date: 27 Mar 90 21:10:49 GMT
Reply-To: patten@uhccux.UUCP (Brian Patten)
Distribution: usa
Organization: University of Hawaii
Lines: 37

I'll quickly summarize my problem:

I have a Mac Plus whose logic board decided to fail.  The local
Apple dealer "tested" it and said the board was bad.  I asked them
exactly what was wrong and they said they couldn't tell me.  A new board,
with labor, is $450.  No way!

When I got the machine home, I decided to remove my 1 meg SIMMS and put them
in safer storage until I decided what to do.  While looking over the logic
board, I noticed that one of the chips near the CPU was discolored and had a 
bubble on the top, near the middle of the chip.  The chip has a dark brown,
burnwed look to it, and I could barely read the numbers.

Okay, now for the questions:

1)  The chip calls itself MMI 341-0519-A 747418.  It has printed on the
board beside it the name "CAS".  It is copyrighted to Apple 85,86.
Can I get one of these chips?

2)  Is this burned chip the cause, or the symptom?  Did something else
fail and throw lots of current through this poor chip, or is this truely
the reason for the failure?

3)  If I try to replace this chip, what kinds of things should I take
precautions against to protect the rest of the board?  I have never
attempted something like this.


Advice on this problem is very much appreciated.  I might also add that
on trying to power up the machine, all I get is a screen with alternating
black and white vertical bars.  The machine does nothing else.


Brian M. Patten
Institute for Astronomy
University of Hawaii
patten@hubble.ifa.hawaii.edu