Kernel Panic under 10.7.5

Same problem here, Late 2009 27" iMac Core i5, 10.7.5 (11G63) ATI Radeon HD 4850

This issue seems to be all over the Apple discussions and Mac forums on the internet. I suspect 10.7.5 (and 10.8.2) included some firmware updates, possibly to the graphics - GPU, that are causing the issue, however Apple don't appear to be owning up to it.

Various people have had success doing wildly different things, e.g. updating SSD firmware, reinstalling 10.7.4 (didn't work for me), changing out memory, SMC reset, etc. but I can see no universal solution in all of this.

I've been able to boot in Safe Mode OK, but even though I have ethernet, internet, email, etc. I can't get to other network resources or use Parallels, etc. I enabled SSH in sharing, and then used PuTTy from my Windows 7 laptop to monitor kernel.log, system.log, so at least I can capture whats happening when it crashes after a normal bootup.

I booted up this morning after leaving it off overnight, seems to be going OK, but I have no applications running apart from the Time Machine backup. In the last few days it seems to crash quicker when I run Safari or Chrome, or Firefox, possibly anything that uses Java or Flash, I don't know. Also if I open a VM under Parallels Desktop.

Its all a bit random.

I've also reduced my display resolution from 2560x1440 to 2048x1152

I have this same exact issue. Screen freezes, if you let it sit there long enough without a hard reboot, it will kernel panic.

Stats

iMac 27 inch, 2.8 GHz Intel Core i7, 12 Gb 1067MHz DDR3, ATI Radeon HD 4850 512 Mb

Mac OS X Lion 10.7.5

I hope Apple will do something about this, it seems to be a very common problem now with 10.7.5 and 10.8.2.

If anyone has any ideas to fix this please holler!

kernel.log

Oct 24 17:49:59 Marks-iMac kernel[0]: ** Device in slot: SLOT--1 **

Oct 24 17:49:59 Marks-iMac kernel[0]: ** GPU Debug Info Start **

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x0000944a

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x000000cd

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000001

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000018

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x0000d062

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000001

Oct 24 17:50:00: --- last message repeated 1 time ---

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x0000944a

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000001

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000015

Oct 24 17:50:00 Marks-iMac kernel[0]: 0x00000000

... This repeats several hundred times after this.

Looks like Apple are finally replacing at least some of the video cards, but only the AMD HD Radeon 6970M in the mid 2011 27" iMacs. http://support.apple.com/kb/TS5167

Those of us with the late 2009 27" iMacs with the ATI Radeon 4850 are still out of luck. Still, its encouraging that after all this time, Apple has admitted fault, and at least some of the thousands out there with these issues will finally get relief. Who knows, maybe they will extend this, but i am not holding my breath. I reckon I should be able to trade in this pile of crap for a 50% discount on the latest 27" iMac!

My machine is running OK, although somewhat crippled because I have had to disable all Quartz Extreme features by removing the ATIRadeonX2000.kext file and having fancontrol on a pretty high setting. I can't watch some videos, my iSight doesn't work in Skype, my time machine is flakey, but I can still do most of what I need to do without Quartz Extreme features. Anything to do with graphics I run on my Windows 7 VM and its just fine, but still a pain.

I would replace the GPU myself if I could figure out where to buy one, how to deal with firmware issues, etc.