PMU Crash fixed

[Clark Martin]

I recently acquired a 400MHz iMac.  It was working fine up to the 
point I ran the OS X installer on it, at which point it says it needs 
a firmware update.  Problem is (and it's a known problem), you need 
the update BEFORE you get the warning.  It mangles the Power 
Management Unit (PMU).  Well in attempting to fix it the PMU crashed. 
This is a state where the computer powers on goes through the boot 
process for about 6 seconds then shuts down.  Well I read numerous 
web pages covering it with similar but different ways to fix it. 
None of which worked.  Well a couple of hours after the last round of 
trying I went over and hit the power button.  And it booted.  Well 
prior to this when it was working I'd managed to download the 
firmware update and install OS 9 (which is required for the updater). 
It booted into 9 and I ran the updater.  One thing worried me, the 
firmware update process includes shutting down the computer.  I went 
ahead with it, not knowing if it WOULD boot up but it did.  After 
that it booted okay with the exception that a couple of times it 
video came up distorted, kind of like it was using the wrong driver 
for the video hardware.  But it was clear enough that I could control 
the computer and a shutdown and startup cleared the problem.

The point of this is that if you run into this problem I would 
strongly suggest keep trying.  The only thing I can say I did 
different the last time was the delay from one startup attempt to the 
next.

If you are having this problem do a Google search on "imac pmu reset".
BTW before anyone suggests it, the PRAM battery was and is good.
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
--
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