19 Oct
1998
19 Oct
'98
4:33 p.m.
Date sent: Sun, 18 Oct 1998 19:24:46 +0100 (BST)
Send reply to: classiccmp(a)u.washington.edu
From: ard(a)p850ug1.demon.co.uk (Tony Duell)
To: "Discussion re-collecting of classic computers"
<classiccmp(a)u.washington.edu>
Subject: Re: 128k Mac Schematic needed
<<SNIP>>
Anyway, to get back the other original problem. Sounds
like the PSU is
tripping. The Mac+ PSU (and the 128 one is similar, I think) is horrible.
It has to have the right dummy loads on both the 5V line and the 12V line
for it to power up. IT takes the regulation sense voltage from the 12V
line. And the chopper heatsink is live (don't ask...).
But my first reaction would be to test (using an ESR meter) or replace
all the electrolytics in the PSU section (lower half of the analogue
board, below the connector that goes to the logic board), especially
those near the logic board connector.
-tony
Thanks. I'll fire up the Ungar and start swapping. I shoulda thought of that -- I
know old electrolytics can go bad, especially in less-than-ideal storage. My
guess is that they were on the edge when I got it, and that one time was
enough to weaken them to the point of failure.
Paul Braun
NerdWare -- The History of the PC and the Nerds who brought it to you.
nerdware(a)laidbak.com
www.laidbak.com/nerdware