A Strange Variation on the iMac G3 Problem

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tmtomh's picture
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Joined: Dec 20 2003
Posts: 568

Hi all,

I'm familiar with all the woes that afflict iMac G3s, but I have a situation that's a variation on the theme, so I'm hoping for some help, or at least some perspective.

The basics:

- iMac G3 slot-loader; 350MHz upgraded to 450MHz via a mobo from a 450MHz unit whose PSU died.

- I upgraded the mobo, added RAM, updated the firmware, installed OS X Tiger, and swapped in a larger HD. Somewhere relatively late in that process, the machine became unstable, often shutting itself down right after startup, and when trying to wake from sleep. The original 350MHz mobo sometimes had wake-from sleep problems, but these never included a shut-down; and with a 400MHz mobo swapped in, the machine had some video corruption (not from the analogue circuitry but from the mobo itself), BUT it ran like a tank otherwise, always waking from sleep and always starting up properly.

- Back to the current situation with the 450MHz mobo - here's the really weird part: I can always get it to start up properly if I zap the PRAM. The PRAM battery is good though, reading 3.57V on my volt meter. I've also reset the PMU via the mobo CUDA button.

- I've swapped HDs in and out, swapped all the RAM (modules and slots), checked, adjusted, and replaced the internal power button (sometimes they tend to get stuck), swapped keyboards, and tried running without a PRAM battery installed. The situation is always the same though - 9 times out of 10 the unit will not start up properly unless I zap the PRAM; 9 times out of 10 it will turn itself off when I try to wake it from sleep; and if it does wake from sleep properly once, it will not do it a second time.

- The common behavior when it shuts down - whether upon startup or upon trying to wake from sleep - is that the HD does not spin up when it is supposed to. So when I turn on the computer, the HD does its initial spin-up, then the grey Apple appears, but then right when the little "spinning gear" should appear and the HD should start loading the OS, the screen gets a darker shade of grey and the computer shuts down. Similarly, when I try to wake it from sleep, the pulsing amber light changes to solid green (as it should), but the HD doesn't spin up, and then the whole machine shuts down.

Any ideas WTF is going on here?

I would chalk it up to the PAV/analogue circuitry problem - but the fact that I can always startup the computer by zapping the PRAM, and that the HD seems to be involved (and keep in mind it's the same with two different HDs), makes me wonder if there's something else going on that I'm missing.

Could it be a hopeless crashed PMU? Is there any possibility that the IDE cable could be to blame? I realize I'm grasping at straws here, but before I give up and part this thing out.
TIA!

Best,
Matt

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Hawaii Cruiser's picture
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Joined: Jan 20 2005
Posts: 1434
I'd probably go back to OS9,

I'd probably go back to OS9, see if the problems persist there. Have you tried starting up from an OS9 CD? Back in OS9, rerun the firmware updates:
http://docs.info.apple.com/article.html?artnum=58174

Or, possibly a bad CD/DVD drive? I don't remember how the jumpers are supposed to be set on the CRT iMac hard drives--master, cs?

I personally, wouldn't go beyond Panther on a CRT iMac.

tmtomh's picture
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Joined: Dec 20 2003
Posts: 568
Thanks for the response, Hawa

Thanks for the response, Hawaii Cruiser. That's good advice.

You've got me thinking that it's firmware-related. Either the firmware update didn't "take" properly, or, more likely, that the updated firmware is just buggy.

I'll try installing OS9 and re-applying the update (if possible). Thanks!

Best,
Matt

tmtomh's picture
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Joined: Dec 20 2003
Posts: 568
WOW - Problem Solved

Well, Hawaii Cruiser, one of your suggestions seems to have done the trick.

I did a fresh installation of Panther, and now the iMac is once again solid as a rock! It starts up properly, restarts fine, starts up fine after being unplugged, and wakes from sleep properly over and over again!

Strange - clearly Tiger doesn't like this machine.

It's also a LOT faster now - which is strange because on similar machines (350MHz iMacs, and 500MHz iBooks), I've found that Panther isn't much faster than Tiger. Perhaps there was some glitch with the Tiger installation, or perhaps Tiger had some problem with the RAM that Panther doesn't?

At any rate, it's running like a champ now.

M