NetNews Usenet Archive 1992 #20/NN_1992_20.iso/spool/comp/sys/mac/hardware/16756

Text File | 1992-09-09 | 1.6 KB | 35 lines

Newsgroups: comp.sys.mac.hardware
Path: sparky!uunet!gatech!news.byu.edu!ux1!fcom.cc.utah.edu!news
From: [e-mail] (James Kleimeyer)
Subject: Flupping Plus
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: University of Utah Computer Center
Date: Wed, 9 Sep 92 17:17:54 GMT
Lines: 24


O.K.- Here's the deal:

Recently, our Plus here in the lab went bad. Upon flipping the power
switch, I got the trademark 'flup..flup..flup' sound of an overvoltage
situation. I had Pina's book at home, so I figured I'd try to fix the
thing myself. The first thing I did was check the analog-to-logic board
connection, along with the solder joints. Everything seemed O.K.. Next, I
swapped the logic board of the bad Plus with my own at home. the logic
board worked fine, so I assumed the problem to be in the analog board. I
checked R56, the voltage adjustment pot. Nothing. I then replaced the
capacitors C3, C24, C25, C26, C29, C30, and C31. Nothing. Then I took out
and tested CR1, CR5, CR20, and CR21. All of these tested fine. I tested
Q8, the 'crowbar' SCR, and it was O.K.. Still, 'flup..flup..flup...' So,
in a fit of desperation, I replaced U1, the LM 324N op-amp.
'Flup..flup..flup...' What in Hell do I do now? Did I overlook something
really stupid? If someone could e-mail me post haste (as we need the Mac
badly here) with any suggestions, I would be greatly appreciative. Thank
you.
--
James Kleimeyer
FFF Research Center, Dept. of Chemistry
University of Utah    SLC, UT 84112
[phone]   [e-mail]  (NeXT Mail)