My computer has a tumor.

Dear Lazyweb, my iMac (Core 2 Duo) keeps locking up. Both screens will go black, and music will keep playing for almost a minute, then the machine becomes unpingable, sometimes continuing to play the last half-second of music in a loop.

Drive passes fsck fine. "Remember" (a front end to memtest) isn't complaining about my RAM. No crash log that I can see.

I can't tell what causes the hang, but it's been happening a few times a day, even when the machine is idle with no screen savers running.

Suggestions on what to check?

I think it might be out of warranty now, since the last time I took it in to the Apple store, they caught on to the fact that I had upgraded the drive to 2TB and wagged their finger at me.

Update: Well now it won't boot at all, with nothing plugged in, or from external USB, so I guess it's "genius" time. I'm assuming it's the video card, which they replaced a year ago. Here's hoping it doesn't take them three weeks like it did last time...

Update 2: Apple has decided that this machine is a lemon, and (with only a couple months left on Applecare) they're giving me a new one for free! So that's cool. They're also letting me upgrade it by paying the difference between the price of the one they were going to give me, and the next model up, so that's cool too. The bad news is, this might take another two weeks (it goes through the online Apple store).

Tags: , , ,

52 Responses:

  1. LafinJack says:

    ...I had upgraded the drive to 2GB and wagged their finger at me.


    • jwz says:

      Upgrading the drive in an iMac involves removing the screen and pretty much disassembling the thing down to the bare metal first, so it's kind of a warranty-voiding process.

      • Jon Lennox says:

        I think it was the "2 GB Drive" that inspired the "what". I presume you meant 2 TB.

        • LafinJack says:

          Nope, I assumed it was either a 2TB drive or an extra 2GB of RAM. I was whatting at how they would be able to tell (presumably at a glance) that someone had done a basic upgrad to their computer. For a place that made the super-cool dropdown motherboard towers and was one of the first to do super-easy removable keyboard upgrades, Apple sure is going backwards on this one.

          • Actually, from what I can tell Apple oscillates wildly every couple of years. Take the iMac G5s for example: The first two generations were really easy to take apart and upgrade the RAM and HD. Then they added the iSight and rearranged everything so that it's basically a huge PITA to get to the HD. You can also look at the iBook G4 (insanely hard to replace the HD) -> non-unibody white Macbook (insanely easy to replace RAM and HD) -> unibody white Macbook (have to remove the whole bottom to get to the RAM/HD/battery). I honestly don't know if there is any rhyme or reason to this cyclical madness, but I'd love to hear about it from anyone on the inside ...

            • Lun Esex says:

              It may be that engineering does something cool that makes it really easy to upgrade part of your Mac, and then Sales hears about it and screams "What?? You made it easier to upgrade than to buy a whole new computer?? Don't do that!" so for the next rev they're chastened and make it harder again. (Repeat.)

              Or maybe it's linked to the cycle of leaves of absence that Steve Jobs has taken...

            • Taking off the bottom of a Unibody Macbook is really easy. I'd rather have to spend 5 minutes removing screws every time I replace the hard drive/RAM (I do this, what, once a year max?) if it means a more robust product.

            • Art Delano says:

              The RAM is accessible through a knockout panel on every generation of the slab iMacs I've dealt with. The hard drives have usually only been accessible through air vents using laproscopic instruments, though.

  2. rodpaddock says:

    If you are running music in itunes I would look if you are running coverflow. iTunes has a bad memory leak in it which could be the problem. Change iTunes to list mode. I would look at the memory that iTunes is consuming.

  3. Well, usually long shot, but the install disc does have diagnostics that exercise more than the memory and filesystem. But if it's out of warranty and it's not those subsystems, it looks like time to pay the Apple Genius piper or get a new mac.

  4. Saying its a "Core 2 Duo" iMac is kinda hopelessly unspecific (There are 5 different generations of them!). The model identifier may be helpful here - Applications -> Utilities -> System Information -> Hardware; the Model Identifier field on the right hand side, which will look something like iMac7,1

    However, I still have no clue. This looks like it could be a 'Fun'* problem to track down.

    (*Yes, 'Fun', not fun)

    • jwz says:

      Model Name: iMac
      Model Identifier: iMac8,1
      Processor Name: Intel Core 2 Duo
      Processor Speed: 3.06 GHz
      Number Of Processors: 1
      Total Number Of Cores: 2
      L2 Cache: 6 MB
      Memory: 4 GB
      Bus Speed: 1.07 GHz
      Boot ROM Version: IM81.00C1.B00
      SMC Version (system): 1.30f1

      • Joe Shaw says:

        I have the same iMac and a similar problem. For me, the screen doesn't go dark and the UI continues to update, but any interaction with the UI beachballs for a minute or so before it locks up entirely.

        Anyway, I was able to track it down to downloading multiple things simultaneously inside iTunes causing (most of) the lockups. Apparently lots of other people have the same issue:

        So if you are downloading podcasts onto the machine, that's a pretty likely culprit. I doubt there is a fix coming from Apple.

        • Joe Shaw says:

          Oh, by the way, since the multiple downloads setting is completely unintuitive to find: go to the Downloads tab -- which is only visible if you're actually downloading something like a podcast or iTunes update -- and uncheck the "Allow simultaneous downloads" at the bottom.

  5. Ray Greenwell says:

    Make appointment at genius bar. Tell them your imac locks up and it might be your video card.

    For them it will refuse to freeze for an abnormally long time. Finally it does, and they say "yeah maybe the video card".

    You leave it overnight, and get everything back in working order for $350. It's like buying your original video card stand-alone, only now it's 3 years later when it should be $35.

    ...That worked for me, anyway.

  6. Hagus says:

    Send me a system profiler report (I guess you can see this email address i just typed in?). That contains enough logs to at least make a wild stab. It's obviously not a panic, so I would guess a gfx hang. Logs plz.

  7. I'd look into a software issue, mac os x memory manager never ceased to amaze me with its incompetence.

    Downgrading itunes could help. I always live new itunes versions as a risky bets.

    Turning COMPLETELY off swap also could help (it's all about *commenting out* dynamic_pager calls in /etc/rc)

    You can check for low memory situations maybe by running a vm_stat redirected into a temp file until it crashes and see if there was still memory or if it was running out.

    If not memory... device driver? Do you plugged anything new recently? how about kernel logs?

    And it could alway be a ram SLIGHTLY out of place. Never happened to me on a mac, but I've seen rams pass memory tests and still be a tiny bit out of place. Could the imac have received *bumps*, have been moved, recently?

    • jwz says:

      It actually crashed once while I was running the memory tester (but then not again) and I had quit all apps, so no iTunes. No new hardware, machine hasn't moved in months. I don't see anything unusual in the logs, but who knows.

  8. Peter says:

    My older (iMac6,1) iMac had a bad video card which I was able to buy from some website and replace. It would hang fairly often but it also got video update anomalies. Replacing it was kind of a hassle, but so is replacing the hard drive.

  9. Dunno how much this applies to the Intel-based iMacs, but where I work we've had plenty of our old iMac G5s die off in the past couple years. Of those there are two broad categories:
    1) Hard drive died
    2) Something on the motherboard let go after being run at a high temperature for the past 5-6 years
    I realize that's not very helpful, but I tend not to investigate too much when a 5-year-old computer dies at my place of employment. For iMacs experiencing problem (1) I've had good luck running them off of an external USB hard drive (Firewire would be fine too, I'm sure).

    Anyways, here's a couple things worth trying:
    1a) Install something that can give you more details about the SMART status of the drive. smartmontools from macports is what I use. I'm sure there's something else as well. Just because it fsck's ok doesn't mean it isn't hosed.

    1b) Even if SMART checks out, it might be worth cloning the FS onto a FW or USB disk and running from it. See if the freezing goes away.
    2) Watch temperatures. Maybe one of the fans has let go or one of the sensors has died and is being interpreted as always always running cool.

    Sorry for the rambling. Hope something there might help.

  10. Lun Esex says:

    Did you also set everything in the Energy Saver control panel to never take effect? Even with that and the screensaver turned off, there may still be a "dim screen" process running that can't be 100% killed via the GUI. It's more for laptops than desktops, but it might still be there as be part of some requirement to get a certain Energy Star rating.

    Try reproducing the problem after booting from your System Restore DVD or an external disk, to isolate the problem from your internal drive and the OS installed on it.

    Have you checked Apple's support forums? They've actually had recalls on defective iMac video cards a couple times. Yours could be one of the affected models, so they wouldn't charge you for an out of warranty repair.

  11. crazybutable says:

    A friend of mine has seen similar lockups and hangs due to firewire problems. Switched everything over to USB and they went away. Probably it was only one device that was failing but he got sick of trying to figure out which one.

  12. Joshuag says:

    I would consider running DiskWarrior.

    My old iMac experienced crashes like that which presaged a complete death of the hard drive, even though my experience over decades of hardware ownership to that point led me to suspect every other cause besides the disk.

    Also, take a look in ~/Library/InputManagers and see if there are any little nasties residing in there. Some developers unaccountably abuse cocoa's text input extension mechanism, and misbehaving inputmanagers can definitely lock your shit hard.

  13. Jay Parser says:

    That line wasn't introduced until April 2008. If you bought the 3 year warranty, it is highly likely it's still covered. Drop the serial number into to find out. It is highly unlikely Apple would have voided your warranty in the repair incident.

    That particular iMac line has been very reliable. Of all the comments, only flaky Firewire cabling sounds at all plausible. (Somehow FW can grayscreen of death a mac with a single fart) A dead fan leading to overheating might also apply, but usually that's preceded by screaming fans.

    This is very likely to be some logic board retardation, and it's not going to be worth your time to fuss with looking at memory or the HDD. (Disk Utility/fsck would probably be reporting HFS+ corruption if the drive was wonking out, and that doesn't seem to be the case).

    Let Apple retail or a Mac shop run their diagnostics on it so you can get a repair moving before the warranty expires. The shop diagnostics are much better than the ones that come with the machine.

    A more DIY option would be to place another Mac in Firewire Target mode (hold T at boot), connect it to the dying mac with a FW cable, and boot the dying mac off of that known-good Mac. (hold Option at boot, choose the remote drive) If it holds up for a day or two, the hardware's good and you need to build a new OSX image for the dying mac.

    • jwz says:

      I believe the machine is still under warranty, I'm just worried that they're going to deny it because of the drive, since they noticed it last time. If they start going down their usual "let's replace everything until something works" script while I'm not under warranty, it could end up costing enough that buying a new computer makes more sense.

      They replaced the logic board and GPU on this machine in July when it started having thermal freakouts.

      That took them three weeks, which was awesome.

      • Jon Konrath says:

        What estimate did they give you before the three weeks? I'm curious because I just brought my 2010 MBP in Thursday with random freakouts similar to yours and they quoted 5-7 days, and the idea of clomping away on this 2007-era MacBook not-pro for the rest of April is freaking me out.

      • Jay Parser says:

        They will be very unlikely to deny it. If they were to deny it or if the warranty is expired then yes, it's time to dump this lemon and move on. A flat rate depot repair (and I use that term loosely) could go up to something like $700. The iMac might continue to function properly as a mini-Displayport slave display, or it might make a lovely sound hitting the bottom of the dumpster.

        There is no good reason for the prior issue to have taken weeks to resolve. Questions should begin at 7 days, open bitching at 10.

  14. Tyler says:

    Reinstall OS X. I can predict your response.

    • jwz says:

      I would certainly do that, if I had any evidence that this was a software problem and not a hardware problem. Without diagnostics suggesting that reinstalling might be more effective than, say, prayer, your suggestion is asinine. Thanks, though!

      • gryazi says:

        People are harfing about clean images; was the USB boot of diverse origin or an identical backup? If the latter, you might want to add "let it sit booted from the install CD see how long it takes to lock up" to your list of dead chickens to wave.

        Also, as I understand it Firewire has that whole "universal DMA" risk going on, so this would be why a flaky Firewire device would be good at bringing down the machine.

        [But I'm still going to bet it manages to be the graphics drivers for some reason, since the open-source Radeon driver happens to have found a way to reproduce the same symptoms on some other hardware I've got here. Convergent bug evolution? Or since your card's got discrete VRAM, is there a way to test the VRAM?]

  15. Sam says:

    Sounds exactly like what my iMac was doing whenever Chrome tried to load WebGL. Go here:

    If your computer freezes again, you know that is the issue. You can disable webgl on about:flags I believe.

  16. I'll give it 95% odds on bad RAM. If the machine has two DIMMs, try swapping them. Memtest can't check the RAM that the kernel already has wired down, but swapping the DIMMs will move the bad bit(s) to a different location in the physical memory map. If the symptoms change, you know you're on the right track. (memtest may not be able to create the exact conditions that cause the RAM to fail.)

    If it only has one DIMM, buy a new one. It's the quickest and cheapest blind fix most likely to work.

    • jwz says:

      Swapped dimms, then ran with only A then only B. Still crashed. Also with all USB devices unplugged.

  17. Graphics card and/or drivers. I had essentially the same symptoms on various Linux boxen (including the half second audio loop) and in every case it was triggered by the video card. In some instances, it was fixed by upgrading the drivers. In others, by replacing the card. Given that Apple have control of the hardware, it's probably not the driver in this instance.

  18. phuzz says:

    It's unlikely, but this set of symptoms could be an overheating issue, possibly in the video card.
    No sodding idea how you'd check component temperatures on a mac though :(

  19. jrishel says:

    I'm with phuzz, check the temperature. try this app:

  20. James C. says:

    “It’s naht a toomah.”

    Screen blank makes me strongly suspect video, and maybe partly overheating. If you can’t get them to accept it under warranty, you can try one thing before you dumpster it: hair dryer on various components to see which one makes it freak out. If you get a positive sign, replace that one thing. If that doesn’t cure the problem, then throw if off the roof it before it becomes a money sink.

  21. Nate Orenstam says:

    good day... your symptoms match my own with an imac g5, except for the sound continuing to play after screens go black. i could find nothing in the logs that indicated a problem. i was seeing this in a fairly hot environment (80+ degrees, in the heart of a west coast summer) and it appears to have been entirely temperature related, as when I moved the machine to a cooler room it resumed working normally. best of luck.

  22. Patrick says:

    Yeah, jumping on the video card bandwagon - that's how my 24" 3ghz C2D died. Random lockups followed eventually by a kernel panic on boot. By then it's definitive and Apple should replace it if you're still under warranty. The general belief is that Magnuson-Moss prohibits manufacturers from voiding warrantees for upgrading user serviceable components unless if they slap a sticker on it saying your warranty is void when you break the sticker. Me, I've never been so sure of that but it sure sounds good.

    Do you have another machine that you could VNC over to the iMac with? As I remember, everything was up (at least briefly) after the video locked up, so I could at least sometimes ssh over to shut it down politely.

    • jwz says:

      When screen went blank, ssh stayed up for 15 seconds. Disk continued gronking for another 45 sec or so. But it's well and truly dead now!

    • Patrick says:

      (in fact, digging in to's descriptions, mine was an iMac8,1 as well. With the NV8800GS GPU, yeah?)

  23. lowellk says:

    Jamie, did you install the 2TB drive yourself? I want to upgrade my HD as well, but would prefer to hire someone to do it for me. I'm lazy lazy lazy.

    • jwz says:

      I did. It was straightforward but took several hours of dis/re-assembly with many fine opportunities to fuck up badly. Skill level moderate.

  24. Ed says:


    Have you tried a SMC reset? See:

  25. Harri Viertola says:

    Check for bulging electolytic capasitors on the main board and also on the videocard. I have no experience on Macs, but usually flaky PC-hardware can be repaired by swapping all of the electrolytic capasitors even if only one of them has tell-tale signs of fluids escaping.