Do I have a Graphics Card problem?

Discussion in 'iMac' started by PannaKO, Sep 12, 2014.

  1. PannaKO macrumors newbie

    Sep 12, 2014
    Please feel free to skim read if haven't the time to read it all, as a complete novice, I'd really appreciate your help.

    My screen started to flicker with colours and black blocks, it seemed to recover after a while, but flickered again and froze completely leaving background noise still playing, the mouse still movable, but the keyboard unresponsive (e.g. volume up/down).
    Now when I try to boot up, there's a chime, the grey screen, then the loading ticker appears, but freezes after a while. There's also some patterns that appear on the grey screen and when using alternative methods of booting up:


    - I tried Recovery Mode, but it freezes, so then I can't try Disk Utility or an OS re-install
    - Safe boot (+Verbose Mode) will also freeze (see results in images)
    - In Single User Mode, FSCK -FY eventually said 'volume appears to be OK'
    - An NVRAM reset just resulted in a louder chime when booting up :eek:


    For some reason my S/N (VM84539P0KM) didn't match the ones on the Apple website, but i believe to be a 24'' 2007 or 2008 Aluminium model that definitely shipped with OS X 10.5.
    I was running the latest version of Mavericks and installed the iTunes 11.4(?) update for the upcoming iOS 8 when the issue occurred.

    I hope you can advise me if it's as easy as taking off the glass screen, unplug old graphics card and plug in new one, as that's as far as my DIY skills go (if it is the Graphics Card) and ow much it's likely to cost if I go through Apple to repair it.

    I'm based in England and at the moment I'm quite far from an Apple Store and any Authorised Repairers so I'm yet to contact them to see if they have some kind of Collection service.
  2. MacVidCards Suspended

    Nov 17, 2008
    Hollywood, CA
    Looks like bad GPU to me, or one that is getting too hot.

    You need to figure out exactly which one you have, some have replaceable GPUs, some have replaceable Logic Boards.

    Ifixit is a good resource to learn what's inside
  3. Brian33 macrumors 6502a

    Apr 30, 2008
    USA (Virginia)
    You may have an iMac the same as or at least similar to mine. I have a 24" Early 2008 iMac (EMC 2211, model A1225), and it came with OS X 10.5 (Leopard): My machine at

    You should try to figure out the exact machine you have. I think I read somewhere that there's an "EMC number" on the bottom of the stand that can be used at to identify your iMac.

    It doesn't look like you've tried to boot the machine in any of these ways:

    (a) from the original CDs that came with the machine (mine are gray with white lettering)

    (b) from an external hard disk drive that has a compatible version of OS X installed (you could make a clone of another or a friend's Mac with Carbon Copy Cloner or Super Duper (cost a little $) or Disk Utility (free but harder to figure out)

    (c) from a USB flash drive/thumb drive with Lion, Mountain Lion, or maybe Mavericks

    so those might be an idea.

    However, I also guess it might be a graphics card problem. My particular machine came with either NVIDIA graphics (can't remember the exact model, but have turned out to be notoriously failure-prone) or ATI graphics like my ATI Radeon HD 2600 Pro (which have "screen freezing" problems for some people but as far as I know don't usually prevent the boot process).

    I do know that the graphics card on my model IS replaceable, unlike some later iMacs. Be aware, though, that it's not as easy "as easy as taking off the glass screen, unplug old graphics card and plug in new one." But it IS do-able, though. With little experience, I've successfully opened mine up and replaced the HDD and optical drive. It helps if you're a patient and methodical type of person. I used ifixit's guide and it was great (for my model,

    Oh, and inside there are some diagnostic LEDs that might help diagnose your problem (though I've never used them). This may help (though I still don't know what exact model you have):

    Good luck!
  4. PannaKO thread starter macrumors newbie

    Sep 12, 2014
    @MacVidCards - thanks for the reply, I think you're right, I forgot to use fan control during this summer :eek:. Although it's been very cool for over a month recently, it did feel particularly hot at the back of the iMac on the day it failed - I'm guessing graphics cards don't always give an indication that they're damaged before failure?

    @Brian33 - thanks for the detailed response!
    After much investigating, it turns out I do also have the 24" Early 2008, and the same NVIDIA GeForce 8800. I had no idea that's prone to failure (I'll be reading up more info about that), but it's good to know it's replaceable. Thanks for the iFixit article and other start up tips, I'll be giving those a try and will post the results.
  5. PannaKO thread starter macrumors newbie

    Sep 12, 2014
    After a lengthy communication process with Apple Customer Service, it turns out my iMac is now considered vintage :eek: :eek: so they didn't have the parts for it and it neither did my closest authorised repairers.
    Strangely, I couldn't find an iFixit article to replace the graphics card, coupled with the fact I got confused in finding the nvidia graphics card model that is also compatible with my iMac, I decided to just try and extract the contents of my hard drive when I'm ready and wait for the next new iMac release
  6. Brian33 macrumors 6502a

    Apr 30, 2008
    USA (Virginia)
    Huh, Vintage! Well, I suppose you'd be happy with a new iMac.

    In addition to the NVIDIA card, your current iMac will also take an ATI Radeon HD 2600 Pro graphics card, Apple part number is 661-4663. (That's what I have, although re-reading my post above makes it sound like I'm not sure, which isn't the case.) I wouldn't recommend putting another NVIDIA GeoForce 8800 in it anyway, since they were so prone to failure, but that part number is 661-4664, if you do want to search for one.

    Unfortunately, a quick web search only produced one Radeon card that claimed to be in stock, for $238:

    Sometimes they come up on eBay, but I didn't see any at the moment.

    Your plan may well be the best. It's rather a shame, because these machines are still very usable. Maybe you can pass yours on to someone who likes to tinker/repair, along with the above information.

  7. PannaKO thread starter macrumors newbie

    Sep 12, 2014
    Yes, after researching the GeForce 8800, I count myself very lucky to have gotten 5-6yrs out of it considering how badly I treated it (never adjusted the fans in the summers in an already hot and humid room). Thanks for the part number (never even thought about using a different compatible card :eek:) I think I'll keep an eye out for the Radeon 2600 for use before I can get a new iMac and then maybe pass it on fully working.

    You're right that it's a very tidy machine, which is probably why I never really considered buying a newer one until now!
    Some posts in this forum suggest selling an iMac after 2-3 years use, as they hold their value very well, and replacing it in a cycle resulting in a far lesser 'upgrade' outlay.
    I'll be looking for the best way to do this as it sounds easy and very practical.

    Thanks a lot for your guidance Brian33, you've been very helpful and informative, I really appreciate it.
    Hopefully the info in this thread will help someone in more ways than just diagnosing/replacing a problematic graphics card, although it's difficult to see someone being as naive as I have been, as you guys have helped me to now realise :eek: :D

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