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Nynax Level 1 (0 points)

I have a late 2009 iMac 27in and a couple hours ago the display glitched out with blue and red squares all over the screen and the computer completely froze. When I did a forced restart the computer booted up with five 1/2" thick sections of vertical blue bars, then at the point where it should leave the gray screen with the apple logo the screen remains gray and the blue bars are replaced with a pattern of tiny blue squares all accross the screen and seems frozen.


The computer does start in safe mode, however, but the 5 vertical bars remain on the screen. What is odd is when I drop the resolution those 5 bars become 4 and change their physical location on the screen. I've done a disk utility check and it said everything was ok...I don't know what to do.


a couple months ago an issue came up where the screen would shut off if the computer got too hot...maybe its just the video card connection is loose? is there a way I can fix that?



I'm very scared right now, this is my only computer and I have NO money. I need to find some kind of DIY solution.

iMac (27-inch Late 2009), Mac OS X (10.7.4)
  • Nynax Level 1 (0 points)

    Just did another test with an external monitor....those vertical bars appear there too....something is really wrong with my video card isn't there :/

  • rkaufmann87 Level 9 (55,223 points)

    I would guess the video card has failed. I'd recommend running Apple Hardware Test in Extended Mode 2-3 times in succession. If the system reports errors then you have confirmed it's hardware and will need to take it in for repair or get the machine replaced. You can find the link to how to run AHT at:



    Good Luck.

  • Nynax Level 1 (0 points)

    Ok, I've tried running the AHT...but the monitor doesnt stay on long enough for me to see the results because of the overheating issue I mentioned...and hooking up an external doesn't work for the AHT of course.


    I expected this thing to last a few more years...I'm prolly going PC after this.

  • MichelPM Level 6 (11,368 points)

    If the iMac was getting too hot and overheating, this may have led to the GPU failing, obviously.

    Every so often, it is good to clear out all of the vents, slots  and ports of dust, lint and dirt. These do get clogged up over time and allow the iMac to get hotter and hotter.

    The GPU in the 27 inch models is a socketed, replaceable chip that needs no soldering skills to remove.

    There are DIY videos to show you how to tear down and reassemble you iMac, however, the issue is going to be procuring the replacement GPU. Apple and Apple Stores will not sell you one direct if you are not an authorized Apple repair center or Tech.

    If you an find an authorized Apple repair center that isn't Apple, you might be able to work out a way to buy this from the repair center if they can order it.

    If you find an alternate authorized Apple repair center, see how much they get for replacing the GPU.

    They may very well be cheaper than Apple's repair rates.

  • Nynax Level 1 (0 points)

    Any Idea what that specific chipset is called? seems to have a number of replacement parts you can order, but im not entirely sure what to look for. thank you for your help.

  • rkaufmann87 Level 9 (55,223 points)

    Look at the Tech Specs for your machine and note which graphics card is installed. You can find the TS on the box or by looking on Apples website. Once you know which card it has then you can begin your search.

  • MichelPM Level 6 (11,368 points)

    Hello Nynax,

    Not sure which model 27 inch iMac you have, but if it had the base 256 VRAM GPU, you can replace it with the same one or you can upgrade to the 512 VRAM GPU.

    I Just went to the WeLoveMacs website.

    They have a service parts section where you can pick the year and model of your iMac and you get a complete exploded view of all of the parts of the iMac that you can order, if they can get these parts.

    The standard 256 VRAM GPU is labelled.


    661-5314, ATI Radeon HD 4670 256MB




    512 MB VRAM GPU is labelled.


    661-5315, ATI Radeon HD 4850 512MB.


    Let me know what these will costs if they can get these as I may try a DIY tear down, myself, in the future, and  upgrade my GPU to the 512 VRAM version. I currently have the 256 VRAM GPU in my iMac, now.

    My 3-year extended AppleCare just ran out as of this coming Fri.

  • MichelPM Level 6 (11,368 points)

    I Did a search on the WeLoveMacs site for the GPU and pricing.


    They are selling the parts for full pricing!

    The 512 VRAM GPU is $300

    The 256 VRAM GPU is $349


    Now that you know the type of video card and its part number for your 2009 iMac, I would suggest doing a general Google search to see of these cards can be had for cheaper.

    I did a quick Google search and already came up with a site that sells this for cheaper.



    So search the web for the best price for these GPUs.

    Best of luck to you!

  • MichelPM Level 6 (11,368 points)

    I Found yet another site that has the 512 VRAM GPU even cheaper, plus this site has videos showing how to tear down your iMac.


  • Nynax Level 1 (0 points)

    Thanks for finding those! that is a big help!



    Tho i wonder, this thing is almost 3.5 years old now.... should I just look into getting a new PC?

  • philsurmac Level 1 (0 points)

    Hi there,



    I've just baked it in oven and it works



    What have I done :



    - heat the oven at 180 degrees (celcius) for 15 mn

    - Put my HD 4850 for 6 mn (3 mn on one side, 3 mn on the other one)

    - the HD was in an aluminium sheet, carefully lied on a plate

    - I removed everything from the GPU (papers, rubbers, thermal paste)



    Now everything is working back... hope it will last

  • zollicri Level 1 (0 points)

    Hello, I've got the exact same issue with HD 4860 512MB.

    Prior to buy a new one, I'll give a shot baking it!

    Please could you be more specific regarding what parts you baked? Once you removed the thermal paste did you put it back? After the baking did you apply pressure on any component (I've read a post about appling light pressure on specific parts after baking)? Thanks!

    PS did it last?

  • philsurmac Level 1 (0 points)

    Hi there sorry to make you wait.


    I removed the thermal paste, the small black foam and other tapes that I found there and there, anything easy to remove. I baked only the square graphic card, all the rest cooling metallic part were removed.


    I bought some thermal paste (artic silver MX2 or something on amazon) to put a new one back, which I think is the thing to do. You could use the old paste, squeeze it and reforming it, but I'd suggest to put a new one quickly : it might be the quality of the paste which killed the card, who knows...


    Me I didnt apply any pressure no, and as for today (1,5 month later), everything is still fine, on BOTH baked graphic card for my both iMacs

  • zollicri Level 1 (0 points)

    Today I baked mine following the same above procedure..... so far so good.

    My only addition was to set the  graphic card on a small pedestal done with balls of aluminum foil.


    Anyone have a good method to keep the IMac cooler?

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