Hello everyone -
I have been trolling this forum for months - since just after the public release of Yosemite. I thought I'd share with others what I have been through (I have posted this in another forum thread or two, as there have been several that have been helpful to me as I worked through my problems)...
I have a mid-2011 27" iMac with the Radeon HD 6770M graphics card. I had experienced the random screen pixillations every 4-6 weeks running Mavericks, and a quick reboot would make the problem go away. As soon as I upgraded to Yosemite, the problem grew immensely worse. Pixillations went from a few here and there on the screen to covering up to half of the screen at once. The screen started locking up, even though background processes were still running (I use SpamSieve and it would continue to filter email while the UI was locked up). The only solution was to do a hard power off and power on. This would happen between 4 and 10 times a day! Incredibly frustrating. I had never locked up under Mavericks, just occasional pixillation artifacts.
So, I reinstalled Yosemite as a new install. And I had the exact same problem. I turned off transparency, turned off sleep, everything I could find as a suggestion here and elsewhere. No change. Pixillations and lock-ups continued.
I finally reinstalled Mavericks. First from a Time Machine backup. I continued to have the same problems that I had experienced on Yosemite! I couldn't believe it, since I had never had the locking up on Mavericks before the Yosemite upgrade. So I reinstalled Mavericks again as a new install... And I still had the issues with locking up and pixillating. I did find that if I set the desktop background to a plain light color (like white or beige) it would pixillate less, and lock-ups happened slightly less. Also, if I used a screen saver instead of just blanking the screen (I used to blank the screen when not in use - iMac stays running continuously - always has since the purchase, other than on trips away from home) then the problems seemed to lessen. Not go away completely, but lessened enough to use the Mac a bit more (it was virtually unusable after the Yosemite upgrade).
Finally, last weekend I gathered the courage, resiliency, and frustration to tear my machine apart, remove the graphics card, and bake it in my oven. You should have seen my wife and kids' eyes when they saw that I was actually baking it! 8 minutes at 290 degrees. On aluminum balls, on a pizza pan.
I was fortunate to have recently received a 13" MacBook Air from the college where I teach, and this has become my main computer since the graphics issues arose on my iMac. I don't know if I would have had the courage to bake my card if I had not have had the security of having the MacBook to use if everything "went up in smoke!"
After letting the card cool down, I put on the thermal paste (from Staples) and put it back on the heat sink, then put everything back together. I booted it up...
and it came up fine! I have been using it here and there every day since (so that's 5 days post-bake now) without the first sign of the pixillation and without a single lock-up. Prior to the bake, I was able to force a lock up "at will" by doing anything that was graphically challenging (open a few Finder windows, open a few Safari windows, open Lightroom or Photoshop, play a video in iTunes, open Evernote... just about anything!). I have not been able to do it once yet since baking the graphics card.
So as you can image, I have gone from being aghast at anyone baking their graphics card (I thought it was the craziest thing I had heard, that there had to be a safer and more sensible solution, and that they were experiencing a colossal "coincidence" of good fortune that it seemed to work!) to being a sold-out believer! My iMac is back and I am a happy camper!
Now, the proof is always in the pudding. I am still half-way expecting the problems to suddenly erupt again. Time will be the only thing that makes me feel better and that it is truly "fixed" now.
I am also still trying to convince myself to upgrade to Yosemite again. My brain tells me it should be no problem now... but my heart says "NOOOO! That's what started all the problems!" Which probably isn't actually true... I'm speculating (like so many others have done now) that there was a fundamental manufacturing problem with the graphics card that grew worse with time (heating...cooling...heating...cooling...), and which was finally pushed to the breaking point by the graphical demands of Yosemite. Now that the card has been "reflowed" it should not experience that "breaking point" again by Yosemite. At least that is what I hope.
So, anyone who is about to pull their hair out (as I was), and who has no warranty, and who lives 3+ hours from an Apple Store, might find some use from my experience.
I would also love to hear from anyone who has resolved your problem by baking and then installed Yosemite since that point. Have you been running Yosemite since then without any graphical problems or lockups? That would help me feel better to do so again myself.
And finally, thanks to everyone who posted your problems, thoughts, trial and errors, baking process, and solutions (and failures). It has all been invaluable to me as I have worked through my problems!
-Charlie
