deadly iMac (experts needed)

Discussion in 'iMac' started by moab, Sep 13, 2012.

  1. moab macrumors newbie

    Sep 13, 2012
    Hello Everyone,

    I hope someone here can help me solve what seems to be an insoluble problem.

    I have a 24" inch, 3.06 Ghz iMac 8,1 Intel Core 2 Duo from 2008.
    It always worked perfectly, except lately it started to have some issues with the audio, i.e. the volume would occasionally get stuck and neither the remote control nor the keys on the keyboard could turn it up or down. However it would work fine again after rebooting.

    Then, over the last days, worse symptoms would add to the sound issues. The screen started glitching, showing some pixelated patterns in bright colours, and the system would freeze, with the rainbow wheel keeping on spinning. Rebooting would again solve the problem but it would happen again after a while, making it impossible for me to work.

    As my 500 Gb hard disk was almost full and I had never updated the OS from Leopard, I thought cleaning things up might help so I decided to erase the whole disk and install Mountain Lion (from USB drive). So I did. The installation went OK, I got to the last stage where it says "you're now ready to use your computer" when it froze again. I rebooted and was able to see the Desktop, everything looking alright. But it froze again. I tried to reinstall the OS but this time it would just get stuck when launching the installer.

    Now it won't boot no matter what. Not in recovery mode, not from USB, not from DVD. Nothing. It gets stuck on the initial grey screen (with yellow glitchy stripes) with the Apple logo and the loading wheel blocked.
    I tried resetting the PRAM and the SMC, still nothing. I ran the Apple Hardware Test and it says there's no hardware problem, the Logic Board appears to be fine.

    Anyone experienced anything similar or has a clue on what can I do before bringing it to an Apple center? I can't afford replacing it or expensive repairs so I'd like to try all I can to fix it myself.

    Thanks a lot
  2. Joesg macrumors member

    Jun 4, 2012
    East Coast, USA
    One thing you could try is booting off an external drive. If that goes well, it might be a problem with corruption in your HDD. If not, it's likely a more serious internal problem.

    To be honest this really does sound like a logic board problem. I'm surprised it was able to pass the tests despite all that has been going wrong.
  3. twistedbydesign, Sep 13, 2012
    Last edited: Sep 13, 2012

    twistedbydesign macrumors member

    Oct 15, 2008
    Do you have the Nvidia 8800 GS? This was the card in my imac from that year. They have very high failure rates (though apparently not high enough for a recall).
    If this is the problem it IS possible to replace the card with an ATI 2600 pro. I read many conflicting reports on this, and it's definitely not an easy task. But i was able to do so just a few weeks ago and return my mac to working condition, although downgrading from 512mb to 256mb didn't thrill me.

    Finding a replacement card is also expensive (mine was about 350) and difficult. You may want to consider replacing the computer unless you are feeling adventurous enough to tear it apart. I wrote down everything I had to do to mine when I made the switch since I had never done it before and didn't want to mess anything up.

    If you do decide to try replacing the card I'll post a step by step on how I did it. I can also double check the model number of the card I got and where i got it so you know you are getting the right one. I know there a few similar ATI cards floating around out there and they won't all work
    I will say it was a fun learning experience (if you are a nerd like me) and my mac works like new now.

    If anyone else wants me to post a step by step on how to do this just let me know. My imac was a 2008 24 inch with the Nvidia GS8800 (8,1) and I replaced it with ATI Radeon 2600HD.

    I guess looking back I sort of highjacked your thread with my experience. I've just been meaning to post about this for a while this seemed like a good opportunity. I would not suggest this fix until you've gotten some more opinions and ruled out other possibilities such as bad memory, HDD etc. I'd hate for you to tear apart your mac and go through all the trouble if this isnt even your issue.
  4. moab thread starter macrumors newbie

    Sep 13, 2012
    Few updates: I somehow managed to boot and go past the initial grey screen. The fan is spinning fast and is loud, it sounds like the computer is about to take off. However I was able to launch the Mountain Lion installer from the USB drive and access Disk Utility. I did "repair disks" and it said everything was fine, so no problem with HDD. I also erased the disk again just in case and then reinstalled the OS. Installation went OK again and I got the "Installation succeeded" message, then it automatically restarted to complete the registration bit where you have to put your name and timezone etc but it got stuck again and the screen glitched.

    The OS should now be installed but when I reboot I still have the grey screen and can do nothing so clearly the problem hasn't been solved.

    @Joesg It sounds like a Logic Board issue to me as well but the test says it's working fine.

    @twistedbydesign Do you reckon a faulty graphic card might be the cause? I thought so too at first but then it's not just screen glitches, it's the whole system getting stuck, could it really be the graphic card interfering so much? Did you have similar problems or was yours just a screen problem?

    Thanks so much for your replies so far guys.
  5. cforand1293 macrumors regular

    Jul 25, 2006
    There is a app that lets you increase and control your fan speed. I have seen imacs running videos get green lines across the screens. You can install this app to help but not fix the issue.

    worked for us, but still not a total fix
  6. harcosparky macrumors 68020

    Jan 14, 2008
    Maybe when he gets his computer fixed he can use that app.

    As his problem indicates he cannot boot the system.

    If he cannot boot, he cannot install apps! :)
  7. mackid1993 macrumors member

    Aug 16, 2009
    I would try booting into an OS X installer or something... that sounds suspiciously like a bad HDD.
  8. pinholestars macrumors member


    Oct 20, 2011
    It definitely sounds like a graphics card issue to me. If you're seeing weird pixels and patterns, it's the graphics card.
  9. moab thread starter macrumors newbie

    Sep 13, 2012
    @mackid1993 I tried to boot in an OSX installer both from USB and DVD but it won't work, it gets stuck. I think it's not a bad HDD as I don't really get the common symptoms for bad HDDs, plus I checked the status of the disk with Disk Utility and it appears to work just fine.

    @pinholestars What I'm wondering is whether a faulty graphics card can be responsible for such a big mess, it's not just weird pixels and patterns, it's the system freezing, the impossibility to boot etc. I hope it's just a graphics card thing as it would probably be the cheapest thing to fix but I'm not sure.

    Anyway, my card is NVIDIA GEFORCE 8800 GT, do you know if it's possible to change it and if so, how can I do that myself?

    Thanks all
  10. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
  11. twistedbydesign, Sep 13, 2012
    Last edited: Sep 13, 2012

    twistedbydesign macrumors member

    Oct 15, 2008
    My issue was just a sudden Freeze, then when I went to reboot it wouldn't get past the gray screen and there was a weird color pattern all over the screen. Like tiny colored rectangles. Hard to explain really. If you google it there might be some better pics.

    Since my issue was so sudden I cant really report on how the graphics card would affect the rest of the system. Mine was working fine, then I left for a week, and the day I got back it just kinda crapped out on me.

    When I get home tonight I'll post more info in the replacement card I got. As I said, it's a daunting task to replace it. But ill at least throw the info up and you can decide from there. Also, as i said, I'll post everything that I did and all the guides I used to help replace mine. I ended up using an ifixit guide for replacing graphics card in 20" imac. There were some differences than on my 24(which i noted) but overall it was a good guide that got me through it.

    My graphic card issue did make it unbootable. So it is definitely possible that this is what happened.
  12. moab thread starter macrumors newbie

    Sep 13, 2012
    Thanks a lot, I'm looking forward to see your replacement tutorial as after doing some research I'm more and more convinced is a graphics card issue so I'll need to replace it myself.

    By the way, I've found someone who experienced exactly the same thing, you can read about it here. My screen actually looks just like that:[​IMG]
  13. twistedbydesign macrumors member

    Oct 15, 2008
    Yeah That's definitely it. Since this is a pretty common issue with those Nvidia cards I'm going to make a whole new post for the tutorial. I wish I had taken pictures as I tore it apart. But I'll do what I can to post helpful links and whatnot.
    I'll start working on the the tutorial tonight. I'll still post info on the replacement card when I get home and post that up as soon as i can. Once the tutorial is up I will let you know.
  14. Bacci macrumors newbie

    Sep 11, 2012
    Although the graphics card could be the culprit, it sounds more like an intermittent power supply issue to me: hardware tests succeed although several components are failing.

    My 0.02$
  15. twistedbydesign macrumors member

    Oct 15, 2008
    Could be. I don't know much about that particular issue. Is there any way to test that? My gut says graphics card just because those cards are notorious for biting the dust. But as I stated before, I'd prefer that everything else is ruled out before suggesting buying a new card and replacing it.


    The product number of the ATI Radeon HD 2600 Pro card replacement is 661-4663. There are several different numbers out there and the cards look mostly the same to me. But this is the one i used so i know it works.

    I got mine from memory4less. I found sites that listed it cheaper but every one I tried said the item was out of stock AFTER i placed the order (It would say in stock on the site, but then I would get a notice saying it would ship when they got more in). This happened to me on 2 sites (ifixmaccomputers and cwioutlet). You might get lucky with another vender that advertises it cheap. But the one i ordered came with heat sync and everything. It was a drop in replacement.

    I will say, it was kinda hard for me to justify spending so much on such an old graphics card (~$350). But at the same time, my mac works great and it was still cheaper than getting a new computer.
  16. moab thread starter macrumors newbie

    Sep 13, 2012
    Yeah I'd much rather avoid tearing my computer apart and spend money on a graphics card without even being sure that is the real issue but I wouldn't know how to test intermittent power supplies. Anyone has a clue?

    @twistedbydesign I read of many people who replaced the card several times and it only worked for days, in some cases minutes, to then crash again. So I'm wondering whether I should just avoid NVIDIA 8800 cards at all or if maybe the newer stocks had the issue fixed? You say your ATI Radeon works just fine even if only 256mb? I do a lot of design work so I'm not sure 256mb could handle it, do you know of any 512mb cards that are still compatible with iMac 3.06GHz early 2008 (A1225)?

    Thanks for your help everyone
  17. twistedbydesign, Sep 13, 2012
    Last edited: Sep 13, 2012

    twistedbydesign macrumors member

    Oct 15, 2008
    the 256 is the only one i can vouch for. If you do a lot of design work you might be better of just gettin a new computer. Depends on how intense the stuff you do is.
    I also read many ppl say that replacing with another Nvidia card didnt last long.

    I guess the other option would be to set the imac aside and hope they decide to do a recall. I thought about that before as well. But who knows if and when that could happen. There may be other 512 cards out there, but i didn't research too heavily. I just went with what seemed the most reliable and the most likely to work.

    If it's any consolation, my room mate and I have done some pretty track heavy recording on an imac 256mb ATI and the only error we ever got was that the HDD was spinning to slow on occasion. I dunno how much garageband and multi track recording stacks up with the design work you do. But the card did seem fine for that.

    Another thing to consider, is that mine was the Nvidia GS8800. You said yours was the GT. I don't know if that means there might be a different connection. The ATI card i mentioned worked for me, but since yours is a higher end imac, there may be some sort of difference. That is worth researching as well before you make any purchases/decisions.
  18. moab thread starter macrumors newbie

    Sep 13, 2012
    Ok good, then I'll try install the ATI Radeon after I read your tutorial
  19. twistedbydesign macrumors member

    Oct 15, 2008
    Hey moab,
    I just started working on the guide. Since I did this a few weeks ago and I used other resources, it will be more of a list of tips and advice with a link to the ifixit guide that I used. The guide is for a 20 inch imac, but it was close enough for me to follow and figure out the subtle differences. I'll still make the guide as thorough as I can and I'll let you know once I post it. I think it will definitely save you some head aches.

    Here's a link to the guide I used, just so you have an idea of what you are in for:
  20. moab thread starter macrumors newbie

    Sep 13, 2012
    Amazing! Thanks a lot for this, really appreciated.
  21. twistedbydesign macrumors member

    Oct 15, 2008
    Ok. I posted the guide up. Just go to my profile and look up my recent threads or posts. I don't post a lot on this forum so it shouldnt be hard to find. If you cant find it or if It gets moved or deleted for violating any sort of rules I'll just PM it to you.
  22. moab thread starter macrumors newbie

    Sep 13, 2012
    Great job, it's a fantastic guide, thank you very very much.
    I see some people say those ATI have conflicts with Mountain Lion, which is the system I'm planning to use so I'll do some more research about it before replacing it.
    I'll let you know how it goes.
  23. twistedbydesign macrumors member

    Oct 15, 2008

    No problem. I've been browsing to find info on the ATI issue but I cant find any reports of it. I'll keep looking. I'm happy with snow leopard but I might wanna try Mountain lion down the road. So it'd be nice to know if there would be any issues.


    Also, I would like to look into exactly which Nvidia card you have. As I stated before. Mine was the Nvidia 8800 GS. You are saying yours was the GT. I don't know if this means the connections will be different at all. If so there might be a different ATI card that you should use. I think they are the same card, but if i find out anything different I'll let you know.


    Ok, not trying to second guess you here. But i'm pretty sure your card IS a GS and not a GT:

    I think they are basically the same card. but the GT is in some other configuration. So the ATI that I listed should work for you.
  24. moab thread starter macrumors newbie

    Sep 13, 2012
    When I run the Apple Hardware Test, in the Hardware Profile Section it says I have a NVIDIA GeForce 8800 GT, not GS. Strange thing is, when I google my card (the GT one) I only get results for PC cards. Also, when I check online the serial number of my iMac to get the specs, it says my model has the GS on it. I'm starting to think there probably is no difference between GT and GS.

    My exact model is the one you can see here. It also differs from yours in that is a 3.06GHz, not a 2.8.
  25. twistedbydesign macrumors member

    Oct 15, 2008
    Yeah. seems the cards are so close that the letter changes are somewhat arbitrary. Either way. the ati should drop right in.

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