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#25077 - 02/19/13 11:31 AM Troubleshooting 21" iMac
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
A friend of mine has a 21" iMac, I believe the Late 2011 model (iMac 12,1--not 100% sure about that, it could be the previous model). This Mac has an intermittent problem which, so far, the techs have not been able to diagnose: intermittently, without warning, it will simply freeze.

It doesn't lose power, or kernel panic--it just locks up hard. This strikes me as most likely a hardware problem. Anyone have any experience with this kind of issue? What should I tell him? Service techs have found nothing wrong--as with all electronics, it seems to have an innate fear of test equipment. My friend has ruled out noisy power (it does it in two different houses), hard drive (surface scan OK, drive is still spinning when freezes occur), bad RAM (he swapped all the RAM for known-good, though I'd expect bad RAM to kernel panic). Anything else I can suggest to him before he takes it out back and shoots it?
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#25078 - 02/19/13 11:36 AM Re: Troubleshooting 21" iMac [Re: tacit]
artie505 Online


Registered: 08/04/09
Has he ever had Activity Monitor > All Processes running on his desktop when the iMac froze?
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#25079 - 02/19/13 02:51 PM Re: Troubleshooting 21" iMac [Re: tacit]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
Intermittent hard freezes can be tricky to hunt down.

Have you tried looping Apple Hardware Test? It may be able to identify the problem. (or it may freeze too, or it may freeze on the same component test every time, or it may run without incident)

Is it still freezing hard when booting off a known good OS (of the same version)?
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#25081 - 02/19/13 03:46 PM Re: Troubleshooting 21" iMac [Re: tacit]
alternaut Offline

Moderator

Registered: 08/04/09
Some of the standard things to try/look into are listed in Joe Kissel's recent Mac troubleshooting: How to handle freezes and crashes. Somehow I don't think that applies here, but it won't hurt to have the list at hand and check the most likely possibilities like hardware test, peripherals, RAM.

I assume that nothing was learned from relevant Console logs? Are the same apps involved in the freezes, or running when they occur? Unfortunately, Artie's suggestion may only be useful when AM's window is visible (including any critical processes) when the freeze occurs.
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#25087 - 02/20/13 10:43 AM Re: Troubleshooting 21" iMac [Re: alternaut]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
I don't know if he's tried Activity Monitor or not. It's something to suggest.

The hardware test will also intermittently freeze, without revealing anything useful (eg, it doesn't freeze at the same place every time). It freezes on a known good OS X 10.6 and 10.7 install, so it's definitively not the operating system.

Nothing in the logs when it freezes--not surprising, really, because it freezes so hard it doesn't seem to have time to write anything. It'd be a lot more useful if it would panic rather than freezing!
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#25089 - 02/20/13 03:21 PM Re: Troubleshooting 21" iMac [Re: tacit]
dkmarsh Offline
Moderator

Registered: 08/04/09

Has he tried a different keyboard or mouse?
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#25105 - 02/21/13 12:05 PM Re: Troubleshooting 21" iMac [Re: dkmarsh]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Good question! I know he's used a different mouse. Dunno about keyboard. I'll have to ask him next time I see him.

It's frustrating troubleshooting intermittent problems. Even more frustrating when the computer isn't in front of me. smile
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#25106 - 02/21/13 12:30 PM Re: Troubleshooting 21" iMac [Re: tacit]
artie505 Online


Registered: 08/04/09
Has he tried running with all peripherals that can be unplugged unplugged?
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#25122 - 02/22/13 02:59 PM Re: Troubleshooting 21" iMac [Re: artie505]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Yep. Ir'll freeze with all the peripherals unplugged.
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#25123 - 02/22/13 03:19 PM Re: Troubleshooting 21" iMac [Re: tacit]
alternaut Offline

Moderator

Registered: 08/04/09
It looks more and more like your initial suspicion could be correct: a hardware problem. You mentioned the HD looked OK, but there's also the HD hookup, although that's less likely to cause problems. That said & FWIW, I have had hard lockups like you describe (or sometimes things would progressively lockup, while it seemed like some apps were still running OK until you put them frontmost) when booted from an external FireWire drive. Since the disk kept spinning I figured it was a FW port issue, transiently bad contacts, you name it. I couldn't get out without a hard shutdown, and never figured exactly what it was, as the drive stopped doing it and behaves normally now (knocks on wood...).
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#25156 - 02/25/13 08:30 PM Re: Troubleshooting 21" iMac [Re: alternaut]
tacit Offline


Registered: 08/03/09
Loc: Portland, Oregon, USA
Okay, so I talked to my friend yesterday, and we discussed some additional troubleshooting ideas.

My initial suspicions were confirmed: the random freezing happens on a known-good operating system, with a known-good keyboard and mouse, and with nothing else connected. He enabled SSH to see if he could SSH in when the computer froze (that would rule out a simple user interface freeze or a defective keyboard/mouse), and when it freezes, nada. It drops off the network and becomes inaccessible to SSH, so it is in fact frozen to the core.

Also, he said that there's a spot on the back of the machine that becomes uncomfortably hot to the touch when it freezes. That, to me, screams logic board problem. At this point, I'm comfortable saying that it's a hardware issue and it's probably terminal, as the cost of a logic board replacement is likely more than the computer is worth.
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#25166 - 02/26/13 06:28 AM Re: Troubleshooting 21" iMac [Re: tacit]
alternaut Offline

Moderator

Registered: 08/04/09
iMacs have a cooling vent inlet below the location where the stand enters the iMac's body. This vent tends to clog up with dust and should be cleaned regularly (w/ compressed air) to improve ventilation. That may not help in this case, but is worth checking anyway, because impaired air flow may lead to overheating and thermal power cutouts manifesting as freezes.


Edited by alternaut (02/27/13 06:10 AM)
Edit Reason: Added additional explanation
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#25200 - 02/28/13 01:32 PM Re: Troubleshooting 21" iMac [Re: tacit]
Virtual1 Offline


Registered: 08/04/09
Loc: Iowa
sounds like it's time to RMC. Reduce to Minimum Configuration.

Not just peripherals. anything you can unplug. internal hard drives. internal cameras, even fans. I was told an interesting story recently from an apple service trainer, he carries this imac fan with him to training sessions. If that fan is attached to the computer, it jams up the internal SMC usb bus (where it communicates its RPMs and temperature) and prevents the computer from POSTing. I thought that was quite the interesting issue. I've never seen that specific issue before, but I've seem similar things. Optical drives are good at preventing ANY device from booting, for example, I've seen that numerous times. Things you wouldn't normally think are related, turn out to be connected in unexpected ways.
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