Sounds like the barrel rectifier at position CR5 on the analog board is
going bad. Tech book I have here says its a MR824 rectifier. I had to
look up the position and the part number in a book I have (Dead Mac
Scrolls), but I have done this repair on a few Mac Pluses (same analog
board as the 128 and 512), and they had similar symptoms. They had the
Chirping noise, as well as the right side of the screen would move in and
out (which would appear that everything is shifted left like you
describe).
Notes from the book. Original rectifier is a GI854, R-SI, 600V, 3A... and
they recommend replacing it with a MR824, R-SI, 400V, 5A to avoid having
the problem come back. The rectifier is kind of top center of the analog
board.
The analog board from those Macs was notoriously flaky. Lots of under
rated parts that burned out easily. Probably Apple worst power supplies.
Ironically, the 2nd worst are the CRT iMacs that brought back that same
style computer. And ironically, the iMacs are bad for the same reason,
under rated components that burned out from normal use. You would think
Apple would have been more careful the 2nd time around :-)
BTW: While you are in there working on the analog board, check and
possibly resolder joint J4 on the main cable on the center of the board.
Its pin 1 on the cable. That joint was bad on I think EVERY Mac Plus I
worked on. So there is a pretty good bet that even if you aren't having
problems with yours now, you will in the future. The solder would split
off the board causing the cable to lose connection, causing the video to
blink out. Smacking the side of the case would cause it to restore
temporarily... its the only time I've had a computer company give me an
official "repair" of "whack the side of the case" =:-O
-chris
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Received on Thu Apr 29 2004 - 14:52:46 BST