Apple iMac G5 bootup problem

September 4, 2008 12:41 PM

Apple iMac G5 (4 years old) dies during bootup

I have a 4 year-old iMac G5 20in with OSX 10.5 Leopard installed which ran fine - although increasingly slow - until this morning, since when every bootup fails. After the initial ping, grey logo, blue screen, and while the pinwheel runs, power is suddenly and inexplicably cut. I have reset the SMU and exchanged the backup battery without it making any difference. As far as I can tell, the capacitors are not cooked. In verbose mode, the screen tells me everything appears to be loading adequately, up to Login Windows Application Started.

Strangely, after several attempts, the bootup got a little further (to the next blue screen) before dying, and eventually, next time, completed the bootup. On completed bootup, the machine clock had reset to January 1st, 2000 - perhaps because of the backup battery exchange.

I've looked at the related issues described in the metafilter threads dated July 14th, 2006 and December 26th, 2007. My problem is similar but different in that the machine doesn't hang but "dies": It sounds like a really sudden power loss rather than an "intentional" power-down. I'm out of (extended) warranty and my machine has undergone a previous repairs of logic board (which failure manifested as bootup problems) under warranty.

On running TechTool DeLuxe 3.1.1 (which isn't fully tested for compatibility with OSX 10.5) it shows HD, VideoRAM, Drive Hardware & Format Check passing OK but it then hangs on the Directory Scan, with the mouse pointer also disappearing...?

I'll definitely go and get DiskWarrior, but even that may have problems seeing that the power suddenly cuts out during bootup? I do have a second iMac though which I could try to use via Firewire cable as described before.

Has anyone out there got a likely spot diagnosis, given the unusual behaviour?

posted by Wilder to computers & internet (9 comments total)

Have you tried booting from the install disk and then running Disc Utility or the Hardware Test?
posted by Thorzdad at 12:52 PM on September 4, 2008

I doubt this is realted, but the laptop I spilled Diet Coke on exhibited this behavior -- it would pretend to start booting, but would then simply fail at some point and shut down.

In my case it was the power supply; fortunately I was still able to pull the drive, stick it in an enclosure and recover the data.
posted by crickets at 1:31 PM on September 4, 2008

Ignore DiskWarrior -- in my experience it's not a terribly useful tool. Instead, boot the iMac G5 into target disk mode, connect it to the live iMac via Firewire, and use the functioning iMac to run Disk Utility on the (potentially) troubled drive. Check both the file system and the file permissions.

If that fails, try the Apple Hardware test and see if any of the components are bad.
posted by -1 at 2:47 PM on September 4, 2008

This happened to me once and the problem was that the vents were blocked by dust and the shutdowns were occuring because the thing was overheating.

This was all diagnosed at the Apple Store and they blew out all the dust and voila, everything was cured!

I've done some of my own dust cleanings on the thing since then and it's worked well just with some compressed air into the ducts. The worst blockage was in the duct on the back right behind the desk stand. It was quite clogged. Also, pay attention to the air ducts on the bottom of the case.
posted by tdogboy at 3:19 PM on September 4, 2008

Agreed. The fact that the power is just cutting off, and that it seems to be happening at more-or-less but not exactly the same time in the boot sequence makes me think it's an overheating issue.

I think the automatic fan regulation doesn't kick in until the firmware loads, so you may not be able to listen for the fan going nuts just before the shutdown -- I imagine that at the beginning of the boot sequence, the fan goes at 100% anyway. But it's worth a listen.

On my PowerBook, which occasionally overheats and immediately goes to sleep, the fan still blasts for a second or two after sleep before it cuts out entirely. When your computer dies, does the fan keep going? How about the lights on the box itself -- do they cut out, too?

-1: DiskWarrior has frigging saved my ass numerous times... I agree that it's probably not going to help out a whole lot in this situation, but it can definitely fix drives with broken directories that Disk Utility wants nothing to do with.
posted by DLWM at 5:04 PM on September 4, 2008

-1 writes "Ignore DiskWarrior -- in my experience it's not a terribly useful tool."

The 500+ gb of data I rescued for a friend from an otherwise toasted G5 tower disagrees with you. It's damn useful, but sounds to me as if it isn't useful in this specific situation. My money's on the overheating - especially if Wilder has a cat. Cat + computer = cat hair felt-coated heatsink, no matter how religiously you clean up after your cat.
posted by caution live frogs at 9:51 PM on September 4, 2008

Was this one of the issues you've already researched? Because I had a very similar problem (immediate power cut) and this was apparently the issue. It hasn't happened since I took my machine to an Apple store and got the power supply replaced. I was a few days out of warranty (of course) but they did it for free anyway. I'd check your EMC number as it explains in the article, then see if you can get them to swap out your power supply.

Apologies if you've already seen this one and it's not the case. Mine instantly died like yours, though -- sounded like someone had flicked a switch.

Good luck!
posted by theredpen at 5:56 AM on September 5, 2008

Seconding theredpen. Mine is in the shop right now having the power supply replaced. It too was past the warranty and extension date but the person I spoke with at Customer Relations kindly amended my file so the repair would be covered.
posted by lunaazul at 2:11 PM on September 5, 2008

Thanks guys - I have to confess it was me, not wilder (my partner) , that this happened to. I was so freaked at the time that I didn't realise it was her login under which I was describing my problem.

As indicated, TechTool stalled/didn't complete it's job and this required another manual reboot, following which rebooting succeeded on the third try (I didn't dare repeat running TechTool). I have had the machine running without shutdown since (i.e. 4 days ago).

Capacitors didn't look to be the problem to me, at least on the basis of a visual inspection. I'm waiting for DiskWarrior to come through the letterbox today. DiskUtility found a few things (hundreds of "unexpected ACLs" under permissions check) and repaired them but I'm not sure whether it will make a difference. In my line of business ACL stands for anterior cruciate ligament (if it snaps, your knee is f***ed), but I'm sure the acronym means something else here.

The dust clogging/overheating/fan issue sounds intriguing and creditable. Next time the machine is shut down I'll explore this avenue. It would indeed explain both the slightly irregular shutdown points as well as the very sudden power loss. I have to say we don't have a pet, but I do take your point, tdogboy and TWLM.

I checked the EMC Number but mine isn't from the 2056 series of machines, so is unlikely to be affected by this known issue (thanks for the link though - I hadn't come across it before on the Apple site ...). Thanks for flagging it up, theredpen & lunaazul.
posted by kairab at 1:37 AM on September 8, 2008