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  • BruceNichols Level 1 Level 1 (0 points)
    I just posted another message before seeing this thread. I'm having the same problem. The more graphic intensive the program - Google Earth expecially - the more noticeable the disruption. In Google Earth large areas of the display and sometimes the whole window are corrupted. It seems like this is a major ongoing issue for Mac. I hope Apple address it soon.
  • blooumpy Level 1 Level 1 (0 points)
    Just contributing with my findings.

    This started happening to my wife's iMac about 2 years ago for we but we've been living with it, and the use of smcfancontrol has sort of mitigated the problem. Due to the recent summer heat, the crashing became too frequently and so I decdide to do something more drastic about it.

    I took the thing apart, clean out all the dust (which I've done in the past), cleaned and as well replaced the thermal grease for both the cpu and gpu with some fresh Artic Silver 5, what a HUGE difference it has made temperature wise.

    Now I have the temperature factor is pretty much under control, even under heavy load, so far I can't get the CPU temperature higher than 52 degrees C - and it now idles at 32 degrees. It used to idle at about 49-50 degrees C and under load i've seen it as high as 79 before crashing. This is with all the fans set to about 2500rpm, I'm sure i can lower the temperatures even more if I max out fan speed.

    However, the problem IS still happening, although much less frequent. The horizontal lines still appear but if I drag stuff around it'll wipe them away almost right away whereas they used to "hang around" for a bit. The machine has hung once while I was working it hard, but I'm guessing the frequent crashing (every 1/2 hour) will go away now making the machine at least usable.

    I'm concluding CPU or GPU temperature is a factor but is definitely not the root cause, at least in my case. I guessing it's bad video ram.

    But who knows... I'll post an update as time passes.
  • binnaeus Level 1 Level 1 (0 points)

    Another victim of the graphics card issue here. I've seen the lines, the triangles, the extra 'stars' twinkling on top of the default starry wallpaper. I've had my share of system freezes and the rest of this.

    As a temporary relief, I removed all the ATI kexts from the extensions folder and installed the fan control. All this made the computer semi-usable. The colorful points all over the screen are still there, especially with dark backgrounds, but at least no system freezes that require a reset or any large graphic distortions are appearing now. But this also caused me to lose a lot of functionality. I would especially like to regain some ability to play DVDs (even if not with perfect quality), to be able to use Preview, Pages, Keynote and a few other applications which now launch as blank white unusable screens that have no content of any kind, at least none that I could see or edit. Especially for that last bit, I'm hoping to regain at least minimal access to use them perhaps by changing some settings somewhere, for instance with Preview, I know the computer can still display photos, because Safari and Firefox for example can do that, but I'm guessing that one or more of the kexts I've thrown away was needed for that. If someone knows a workaround for this particular issue I would truly appreciate it, and I hope your suggestion doesn't involve going back to Tiger or running the computer under safe boot. Thanks.
  • kfuse Level 1 Level 1 (0 points)
    I'm having exact same issue (especially with graphic intensive apps e.g. Google Earth, iMovie and several other 3D apps I use). I first thought the problem was old graphic card on my 2006 MacBookPro, but recently bought brand new 27" iMac shows the exact same symptom. Cooling the CPU reduce the frequency of the event, but I too feel something more major going on.
  • Ian Cheong Level 1 Level 1 (30 points)
    binnaeus wrote:
    ...If someone knows a workaround for this particular issue I would truly appreciate it, and I hope your suggestion doesn't involve going back to Tiger or running the computer under safe boot. Thanks.

    To date the origin of the problem is unclear and therefore there is no universal "fix". My problem has recurred after several months and I'm curious enough to try to find the root cause.

    To clarify the origin of a problem, it is necessary to be systematic. (For details: <>) A safe boot is not a solution, it is a diagnostic step which eliminates most software issues. If a safe boot fixes the problem, the ultimate solution is an "archive and install". If a safe boot does not fix a problem, it is likely a hardware problem or perhaps a core OS problem and one can go to Apple/dealer with that confidence. There is a recall for MacBook Pros with a certain Nvidia GPU. <>
  • Ian Cheong Level 1 Level 1 (30 points)
    It may be there is a combination of:
    - poor ATI graphics driver
    - heat problems
    - Apple underclocking the GPU

    Safe boot apparently does not load the ATI driver (with some resulting loss of functionality).

    So the various fixes can all help:
    - reinstalling ATI drivers
    - sucking out dust; turning up fan speed (smcfancontrol); replacing thermal paste
    - tweaking GPU clock speed

    Further information if you want a long read....
  • Ian Cheong Level 1 Level 1 (30 points)
    In the end, my problem still reliably disappears on safe boot. It suggests that a possible hardware/thermal problem causes corruption of code or NVRAM, which then results in corruption of more system resources (eg prefs files) and the more fatal problem of freeze/crashes.

    An archive/install of OS PLUS zap PRAM appears to solve the software part of the problem. Cleaning out dust +/- running smcfancontrol is worthwhile.
  • Ian Cheong Level 1 Level 1 (30 points)
    Latest recipe which seems to clean up the horizontal line bugs for me which appear on login (still testing):

    1. restart
    2. zap PRAM while restarting (<cmd-opt-P-R>)
    3. restart in single user mode (<cmd-S> while restarting)
    4. run applejack (not sure if it is preinstalled, if not download from htp:// - run at least options 3,4,5. 1 and 2 take a lot longer and recommended if you have lots of time. When asked if you want to clean caches and prefs in specific user accounts, say Y and clean out any user accounts having problems
    5. restart after finishing applejack
    6. zap PRAM while restarting
  • Dave13 Level 1 Level 1 (25 points)

    Just to add another voice...

    White iMac Late 2006, OS 10.4.11: horizontal lines started to appear after about 2 years, but now also frequent freezes.

    Downloaded smcFanControl v 1.23 but it refuses to run on 'unsupported machine'

    Message was edited by: Dave13
    Sorry, my mistake, smcFanControl v 2.2.2 now installed
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