I found a solution - though I'm not exactly sure why it worked.
I did an erase-and-install of Panther (someone at 'fritter suggested downgrading to Panther, saying "iMac G3s don't like anything higher than that." That wasn't my experience, but I figured what the heck).
Since I did that, it's like a new machine - rock-solid. It boots up properly every time, wakes from sleep, warm restarts okay, and boots properly after being unplugged for a little while.
So my conclusion is that the problem is/was one of three things:
(1) Tiger didn't like the RAM and Panther is more tolerant;
(2) Panther is somehow more tolerant of a wonky PMU;
(3) Some combination of the above affected the firmware update I did to prepare for OS X, and for some reason Panther is more tolerant of whatever's going on in OF than Tiger.
(4) Something strange happened with the original Tiger install and/or update to 10.4.11 and associated updates, that perhaps corrupted some System caches or kernel caches.
I would be inclined to think it was number 2, except a messed up PMU would, I imagine, cause problems with any OS X version; and because I was very careful when resetting it, and even removed the battery and let the mobo sit for awhile before doing so to make sure it worked (I put the battery in before actually pressing the button, as Apple prescribes for this model).
It's very strange though, because no matter what the problem is, the difference is so black-and-white - not only would Tiger crash, but it would shut the computer down, while on the other hand Panther is totally stable, without even a hint of any problems.
The other strange thing: Panther runs much, much faster. Usually on these 350-500MHz G3 machines (iMacs and iBooks), Tiger is about as fast as Panther.
Oh well, who knows - the end result is that this iMac is now running great!
M
I did an erase-and-install of Panther (someone at 'fritter suggested downgrading to Panther, saying "iMac G3s don't like anything higher than that." That wasn't my experience, but I figured what the heck).
Since I did that, it's like a new machine - rock-solid. It boots up properly every time, wakes from sleep, warm restarts okay, and boots properly after being unplugged for a little while.
So my conclusion is that the problem is/was one of three things:
(1) Tiger didn't like the RAM and Panther is more tolerant;
(2) Panther is somehow more tolerant of a wonky PMU;
(3) Some combination of the above affected the firmware update I did to prepare for OS X, and for some reason Panther is more tolerant of whatever's going on in OF than Tiger.
(4) Something strange happened with the original Tiger install and/or update to 10.4.11 and associated updates, that perhaps corrupted some System caches or kernel caches.
I would be inclined to think it was number 2, except a messed up PMU would, I imagine, cause problems with any OS X version; and because I was very careful when resetting it, and even removed the battery and let the mobo sit for awhile before doing so to make sure it worked (I put the battery in before actually pressing the button, as Apple prescribes for this model).
It's very strange though, because no matter what the problem is, the difference is so black-and-white - not only would Tiger crash, but it would shut the computer down, while on the other hand Panther is totally stable, without even a hint of any problems.
The other strange thing: Panther runs much, much faster. Usually on these 350-500MHz G3 machines (iMacs and iBooks), Tiger is about as fast as Panther.
Oh well, who knows - the end result is that this iMac is now running great!
M