14 Replies Latest reply: Feb 8, 2013 11:46 AM by l3c
l3c Level 1 (0 points)

iMac 20" (Late 2008)

2.66GHz Intel Core 2 Duo


ATI Radeon HD 2600 Pro 256MB

OS X 10.8.2


I am having a few issues with the iMac, it seems every couple of days the iMac will just radomly freeze up. Being a computer engineer and knowing the iMac was out of date i thought it was because it was getting to hot so I stripped it down and cleaned out the inside and the fans. This did not cure the problem as it just froze a few minutes ago.


When the iMac locks up sometimes the screen is still showing what I was doing but I cannot move or do anything, one time I have had a white screen and most of the time its is a dark blue. When I reset the Mac it works perfectly fine and boots up nice and quick, also it is not hot at all.


When this happens there is normally only 2-3 programs open (Chrome, iTunes and maybe Skype), also when it freezes sometimes the music is still playing in the background and then that will stop about 30 seconds after.


Is there anything else I can do to solve this problem or a check I can do to see what is causing it?

iMac, OS X Mountain Lion (10.8.2)
  • a brody Level 9 (65,360 points)

    Have you run the hardware test that came with the computer?

  • l3c Level 1 (0 points)

    Hi, how do I do that?

  • l3c Level 1 (0 points)

    dont worry i got it.


    thanks i will do that and let you know.

  • l3c Level 1 (0 points)



    Over the last few days I have still not been able to get in to AHT, so I have now replaced the thermal paste on the CPU and the GPU which still has not seemed to cure the problem. I swapped the RAM over a while ago and this problem never occured before that, I am now considering swapping it back over for the old RAM to see if that changes anything.


    I will let you know if it works.

  • a brody Level 9 (65,360 points)

    Thermal paste is one of those rock and a hard place problems.   Too much, you give it too much insulation. Too little, and it overheats on its own.  It is best to let an authorized service technician do a thermal paste application if you aren't one yourself, as only they know the exact amount that will qualify for the equipment.

  • l3c Level 1 (0 points)

    Luckily I work in a PC repair shop and repair PCs and Macs all day long so I have an idea what I am doing.


    As I said the thermal paste didnt cure the problem but everything else is still working perfectly normnal, I have swapped the RAM to another two 2GB DDR2 peices which has again not cured the problem as it froze on me the other night. (I put it to sleep and it would not come of sleep mode, it just had a black screen)


    I am now moving on to my last idea of doing a complete clean install of OS X Mountain Lion.


    I am pretty sure it is something really simple as I never had this problem before I upgraded the OS or the RAM.


    I will let you know what happens.

  • MichelPM Level 6 (10,595 points)

    Is the RAM to Apple's specs?

    Macs are very picky about RAM and just can't use any ole' PC RAM.

    Here are the proper RAM specs for your model iMac.


    6.0 GB (Actual) 4.0 GB (Apple)
    Memory Slots2 - 200-pin PC2-6400 (800MHz) DDR2 SO-DIMM


    Reliable Mac RAM can be purchased cheaply from online Mac RAM vendors Crucial memory or OWC (aka macsales).

    This maybe your issue.

  • MichelPM Level 6 (10,595 points)

    Another concern

    4 GBs of RAM in your iMac is enough to run OS X alone, by itself.

    Every new iteration of OS X uses more CPU, GPU, RAM and hard drive resources.

    OS X needs to have a working minimum RAM amount of between 2-4 GBs to do its thing smoothly, quickly and efficiently.

    Start running additonal apps atop or along with OSX and your iMac slows in performance and may, on occasion, crash.

    Since you like leaving applications running in the background, I would recommend installing the additonal 2 GBs of RAM to bring your iMac to a max. of 6 GBs of RAM.

    This should help you with some of your issues if it isn't hardware related.

  • l3c Level 1 (0 points)

    So are you saying my iMac will support 6GB of RAM.


    I am sure the RAM I am using is compatible because else it wouldn't boot, right?


    I'm at work at the moment so when I get home I will give you the specific details of the RAM. When I got the RAM I made sure that it was compatible.


    We will see...

  • MichelPM Level 6 (10,595 points)

    Tthe RAM has to be to the exact specs.

    No variation.

    And no, if the RAM spec is close, it may indeed boot up, but the Mac could exhibit issues right away or may have issues that could happen over say a few days to a week.

    If your IMac is crashing, it maybe that the RAM is not quite be the proper specs.

    Crucial memory and OWC have the proper and reliable RAM for Macs.

    If you bought this RAM locally at some electronics or computer store, I can almost guarantee it's not proper spec'd RAM.

  • MichelPM Level 6 (10,595 points)

    And yes, OWC has determined that your model iMac can take 6 GBs of RAM.

    OWC tests every new Mac that comes out to see if they can take more RAM than Apple recommends.

    Some, but not all Mac models can take an amount of additional RAM over what has been tested by Apple.

  • l3c Level 1 (0 points)

    I got the RAM from my work and i made aure that it was exactly the same make and speed as the ones that were already installed.


    What i will do is put the very original RAM back in and see how that goes.

  • a brody Level 9 (65,360 points)

    Getting the exact speed is not necessarily sufficient.  Timing has to be exact.  That's often not fully published.   Only vendors that sell RAM by Mac model name & vintage are known to give you the correct specs*:  http://www.macmaps.com/badram.html  OWC (macsales.com) is one of them.

  • l3c Level 1 (0 points)

    I have now place the original RAM back in to the iMac which it seemed to like for a bit until it froze up again, but with this RAM it lasts a lot longer than it usually did.


    I have now done a complete clean instal of OS X Mountain Lion and put back in 2x2GB of DDR2 6400S RAM and it froze on the first day(today).


    The only other option I can think of is to change the HDD.


    Another thing aswell it is warm at the top of the Mac which makes me think either the HDD is getting hot or the Logicboard is as I have cleaned the whole thing out before.


    Also for the first time it froze but I could still move the mouse but could not click on anything, I have seen a lot of people on the forums with this issue. Hope that helps.