24" iMac Screen Freezes since 10.6.3 update - pls help!

SWMASTER - thanks for this full screen of nonsense - I'm sure it fits the bill if you're an f'n physicist. My imac crashes. It gets a white screen. Sometimes twice a day... and I need an f'n degree in computer science to fix it?!

Why can't apple release a kext patch or an update to fix this prevelant crash with a single click? Because they don't want to it seems.

I followed the instructions for rolling back the kernel drivers midway through this thread, and everything worked out okay; until my iMac started re-experiencing random white screens during use. Yesterday I rolled back the kernel drivers after finding out my wife had let Apple update the software (I'm assuming that meant replacing the 10.6.2 kernels), only this time when rebooting, the screen went white, and stayed that way for about 6-7 minutes, with each moment of progress taking an age. When the desktop was finally there in full, I couldn't move the mouse 1-2mm without a long pause, and it's stayed that way since. I tried to reset the PRAM, which did nothing, and now the only way we can use it is in safe mode.

The last thing I want to do is take it in to Apple, but I'm stuck as to what my next option might be? I've searched online and found little bits of info, but I'm suspecting the roll back of the kernels is behind this total gridlock. I've also upated the software, which has made no difference too.I bought the unit second hand and sadly don't have the install discs, so haven't been able to explore that avenue as yet. Can anyone help?

Hi,

I have an iMac 7,1 (Late 2007) but my problems are little different. My machine freeze only in certain situations:

1) Exploring time machine

2) Using Top sites in Safari

3) Play quake live or other games.

I also noticed that my temps are very high compared with yours:

GPU: 69°C

GPU Diode: 72°C

Is there a way to better cool my GPU?

Thanks in advance.

Alessandro

@Mac,

i had the same experience (lagging cursor movement), as i was trying to find out, which of the kexts is really needed. i experimented a bit with various versions (e.g. the latest version from ATISupport and the 10.6.2 ATIFramebuffer and ATI2400Controller).

what it proved to me, if any of those kexts fail to load (ATISupport, ATI2400Controller (or 2600 if you have the better GPU), ATIFramebuffer) - yeah, it can happen if you have inconsistent versions installed - you end up hawing white screen (if unlucky) or very "stroboscopic" mouse movement, and impossible slow reaction when using the GUI.

you should check, what do you have on your iMac using Terminal. just type "kextstat | grep ATI" and you'll be presented a list like this one:

imac:~ swmaster$ kextstat|grep ATI

103 2 0xffffff7f8165c000 0x46000 0x46000 com.apple.kext.ATISupport (6.0.6) <69 10 9 7 5 4 3 1>

104 0 0xffffff7f81fa4000 0xca000 0xca000 com.apple.kext.ATI2400Controller (6.0.6) <103 69 10 9 5 4 3 1>

105 0 0xffffff7f816a9000 0x2cc000 0x2cc000 com.apple.ATIRadeonX2000 (8.0.0) <72 69 10 7 6 5 4 3 1>

107 0 0xffffff7f8206e000 0x12000 0x12000 com.apple.kext.ATIFramebuffer (6.0.6) <103 69 10 9 7 5 4 3 1>

as you se, i have the most recent version from ATIRadeonX2000 (8.0.0 - it's from mountain lion) you don't mess with that, or you will start getting kernel panics.

the other kexts are version 6.0.6, e.g. from the "last know good" 10.6.2 update.

there are a couple of things you have to pay attention when installing the kexts. it actually doesn't matter, what way you use to install them (the terminal way or the kexthelper way), but at the end you have to make sure

- all the newly installed kexts are owned by user root and group wheel

- none of them is writeable by anybody but root

- none of them has extended attributes

otherwise MacOS will not load them, and you end up with the current issue. "fixing permissions" will do the trick, but it takes time.

kext caches need to be rebuilt properly, otherwise MacOS will boot the old cache with the "non-working" ATI drivers from your recently updated OS version (say 10.6.3+, 10.7+ 10.8+) and you still get the freezes.

it should happen automatically, as you change anything in the folder "/System/Library/Extensions".

but it takes time, sometimes a couple of minutes.

as i experienced, Lion and Mountain Lion automatically delays the shutdown/restart procedure if there is a kext cache rebuilding in progress.

you can check anytime, when your kext cache was rebuilt:

on lion/mountain lion type in terminal:

imac:~ swmaster$ ls -la /System/Library/Caches/com.apple.kext.caches/Startup/kernelcache

on Snowleo it's:

imac:~ swmaster$ ls -la /System/Library/Caches/com.apple.kext.caches/Startup/Extensions.mkext

the file date will tell you what you need to know. mine is ML, and it was built on 29.07 6:18pm

-rw-r--r-- 1 root wheel 15988456 Jul 29 18:18 /System/Library/Caches/com.apple.kext.caches/Startup/kernelcache

it you see, it's not recent (say you rolled back the 10.6.2 drivers today, and the cache is from yesterday), you can force a kext rebuild easily by typing this in Terminal:

imac:~ swmaster$ sudo touch /System/Library/Extensions

kextd will notify it, and automagically start kextcache utility to rebuild the caches. (this works on ML and L, i do not have SL installed anywhere to test this). wait a bit, and re-check the kext cache date using the previously shown way.

hth,

swmaster

Just saw your comments swmaster, and I'm going to follow your instructions and report back ASAP!

I just tried the kextstat I grep ATI command and nothing happens. have I mistyped it?

You mentioned that it's possible to reinstall the 10.6.2 kextstat via Terminal, perhaps I could try doing that and see if the problem gets resolved, because while my iMac is working in Safe Mode, I'm unable to access kexthelper.

I had experienced kext panics since back in 10.6.2. I read all posts and tried everything. I went so far as replacing my CPU with a 2.8 Intel Core duo chip with no change in crashes. iMac always booted and worked fine in safe mode, indicating software problems. Reading cresh reports indicated a different extension and app each time. I deduced that there must be something common to all failed extensions. I found that font conflicts were ALWAYS involved. In Fontbook I validated fonts to find many "minor" errors. These do not indicate errors in the fonts themselves and often indicate conflicts. I resolved all the conflicts and eliminated Helvetica fractions font which I know from previous posts caused trouble. After 2 years of struggles with many types of screen freezes. I now have a trouble free (and because of the CPU upgrade) iMac screamer. I called Apple care to inform them of my discovery and they indicated that it was worth looking into. It's an easy fix and worth a try. Good luck all.

@bobzart

Could you provide me with a step-by-step walkthrough if possible? I trust it can be done while in safe mode?

Thanks 🙂

@bobzart

I've just looked in my fontbook folder and Helvetica Fractions isn't listed.

Just to update, I tried the 10.6.2 Driver rollback process again, and amazingly everything's back to normal! I'm so relieved, and can only hope things continue to remain stable. Thank you to bobzart and swmaster for your efforts.🙂

Just to clarify: it is Krzysiu Turek who resolved this problem with the kext fix. Notwithstanding 81 pages (and counting) of problem descriptions and suggested fixes, his is the only fix that works without a hitch across Snow Leopard, Lion and Mountain Lion. No offense to others with ideas about fans and fonts and such. But the definitive solution to this problem - other than paying for a new graphics card for an old computer - goes back more than a year.

goskip40 wrote:

I used the kext helper which worked cleanly within a few seconds, but the reboot did hang which concerned me a little. I needed to kill the kext helper from the Unix prompt before the system rebooted. After experiencing a hang my heart was in my mouth for a few seconds, but was relived to see it boot properly.

Yes, Kext Helper always hangs after doing a kext change. I wonder if this was ever fixed. Does someone know who the developer is or if it has a website or something?

Agreed. And isn't that a scandal for "the world's most valuable company of all time," Tim Cook?

I know there is a lot of talk about the freezing and such on these forums. I am wondering what people have been doing with their machines that freeze. Are people buying them or can they get fixed?