[archaica]

I've got an odd problem with an iMac G5 (rev.C) and wondered whether anyone else here knows about it.

It started with occasional freezes. My first thought was to check the hard drive, so I booted off the install CD and did a Verify Disk in Disk Utility. It reported some problems it couldn't repair. The next day it couldn't get past the gray screen with Apple logo when booting (fan going full blast too). It all seemed like hard drive death, which didn't surprise me much since it's about 4 years old now.

So I got a new SATA drive, opened up the machine, and put in the new drive. Everything seemed fine for about 12 hours, then the same thing happened - machine seizing up, then only getting partway when booting. Hardware Test seized up when checking the new hard drive.

I took the new drive out again and put it in an external case and hooked it up to a different machine. Checked it with Disk Utility and all was fine. Suspicious now, I took the old drive and put it into a different iMac (G5 rev.B). It booted fine, and ran with no problems.

So I'm wondering, is there some other problem that would make it look like the hard drive is going bad?

Thanks for any suggestions.

[reader50]

The G5 iMacs got hit by the bad-capacitors problem, mostly affecting the power supplies. The symptoms are usually unexpected shutdowns though, rather than freezes.

Boot into Apple Hardware Test, do the RAM tests. A RAM stick gone bad will cause all manner of problems.

[seanc]

A revision C iMac with bad capacitors?

Rev A was guaranteed, some B had bad caps, but I've not heard of rev C having many problems.

I agree with the RAM theory though.

When the iMac freezes, do the fans get noisy?

[chipchen]

I would second the bad capacitors... open it up again... check for leaking/blown capacitors... basically, iMac G5s are like xbox RROD... it's not a matter of it it will die, but when...

[imitchellg5]

Power supply is toast.

[archaica]

Thanks all. RAM tested OK, and swapping in a new DIMM didn't help, but when I took out the power supply, two of the caps had a slight bulge. I also didn't realize the bad capacitors hit rev C, but it looks like that must be it.

[P]

The bulging caps come from the liquid electrolyte in the cap boiling over into a gas as temperatures rise, moving it away from where it was supposed to be and leaking out into the outer can or out on the motherboard. This happens with heat, and high load makes the cap hotter. This has always happened, to some extent, but it has become much more frequent in recent years. The main problem is that power reqs grew quickly in the early ears of this decade, and power supplies grew to compensate. In this race to reach capacity, reliability was left behind and we are only now beginning to catch up with the transition to solid state caps.

The specific bad batch - the "capacitor plague" that affected Dell and Apple among many others - came from a bad formulation of the electrolyte, where one manufacturer allegedly stole a formula that was still in development, thinking it was done. If you have one of these capacitors, it WILL fail sooner or later. It affects many Rev. A iMac G5 (but not all) and some Rev. B just at the beginning of the run. Rev C is not affected, but can of course die as well just as any other piece of electronics - especially if the venting has been less than optimal so the computer has run hot.

[seanc]

Indeed heat will kill a capacitor.

I would suggest you need to be looking at a new power supply, unless you're proficient with electronics.

I've still not managed to revive my Rev A, although something else is wrong with that after having replaced the capacitors, I've still got no power.