Q: Red and green square dots?

No this is a problem with a defect in the graphics card.  All the baking you see mentioned above in the thread effectively re-flows the solder. The hypothesis is that the solder has developed miniature breaks that are agitated by contraction when cold.  I can say with 100% certainty that everything I did up until baking my card did not work.  It was my last ditch effort, and was completely successful.  It's been a couple months now and I have not seen a single artifact, and have not had a single freeze up.  If you have access to a heat gun you can get the same results with targeted heat. 

I have the same issue with the large dots. It only happens when I have a video selected in the finder. When I have a .MOV, .MP4, etc. selected in the finder, both of my displays are covered with these large dots. If I click away from the video file, the dots will remain until the display refreshes by me clicking on the application window beneath the dots, etc. If I select the video file again, the dots all come back. I haven't seen a solution in this thread (I've read a lot of the posts, but not all). I have a 2010 iMac, 27 inch, 2.8 GHz Core i5 running 10.7.5. Just started happening in the past few months. I've seen a few posts about uninstalling Chrome to fix it. Does that work? And if so, why? And doesn't seem like a long term solution since I need to test in chrome.

I've had a bad time with the red and green blocks for a while.

The last two days where a **** with constant crashes and reboots.

Desperate to get the problem solved I baked my Ati Radeon 5870

What a ridiculous idea, really!

It has been an hour after the baking and the squares have not appeared yet.

So my baking method is the same as the others; 200 degree Celsius, preheat oven, then exactly 7 minutes in the oven with all the plastic parts facing down. Did not repaste the heat sink or whatever. I let it cool for a while and reinstalled it in the MacPro 2009

I hope I will not have to post in this discussion all in tears... fingers crossed.

PS do they have ovens behind the genius bar?

You're correct TheDoctorG.  I am now able to offer yet another confirmation that baking does resolve the issue.   Thanks to Richlove and all the others for taking the time to post their experiences and results.

For those of your who think that being insistent, polite or whatever to get your cards replaced are just spinning your wheels unfortunately.   As others have repeatedly pointed out, those replacement cards have the same issue and will ultimately show up again with the "new" cards which in reality have been sitting in a warehouse somewhere for 3, 4 or 5 years.

I am a Mac guy now, and have been since 2003.  Prior to that, I built my own PC's and I am an IT Network administrator by trade.  I don't work on Mac's in a business environment, so I didn't have the suction cups and to be completely honest, I had never even seen the inside of my own 2010 27" iMac until yesterday.  Not sure why, but I was actually nervous to do this, and I put it off and stayed on Mavericks as I too had horrible results trying to upgrade to Yosemite.  My iMac works great in every other respect, and I felt I was forced in to going ahead with the bake simply because I wasn't going to waste money on a repair that I knew wouldn't ultimately fix it, I couldn't sell it in good conscience, and I couldn't throw it away and buy a new one knowing that the problem was actually so minor. 

I ordered the cups from iFixIt, and went ahead and grabbed a new set of the tools while I was there.  I very cautiously took my iMac apart following the instructions posted in this thread previously.  Baked at 400 for just over 6 and a half minutes (oven was preheated).   Once the card had fully cooled, I applied fresh heat sink compound and put it back together.  It struck me on the re-assembly that it really isn't all that different from taking apart any computer, but for some reason, the Mac's just had this mysticism in my mind which made me nervous.   I cannot explain why that was the case, it just was.   Booted up, no issues!   Upgraded to Yosemite, no issues.   Ran for 24 hours, still no issues, with power saving back on and using it as I normally would for both low stress and high stress activities (like games).

I cannot recommend this for anyone who is not VERY comfortable with working inside a computer.   For those folks, I know you're frustrated, but rather than going to Apple, who unless they install ovens at the Genius Bar is actually unable to permanently resolve the problem.   Find a local computer store who will work on Macs.   Show them this thread and ask if they are willing to do the work.   A lot of those folks have probably heard of the baking method as it's not a new procedure for fixing this kind of issue with circuit boards.  Even if they won't do the bake at the local store, they may be willing to remove your card and reinstall after you do the bake yourself.

5 days, still no issues, Bake-it!

Two weeks now and the spots came back.

I was watching a flash movie in Firefox and the vents of the CPU started spinning loudly, two minutes later the first squares reappeared. Flash in full screen grilled my GPU!! I'll send you a bill Adobe grrrr

Really?   Correct me if I am wrong, but I think you are the first to have failure after baking.   Is the problem the same as before or different?   I think we baked around the same time, and I am still doing well.  

The problem just started and has occurred twice in 10 hours and seems smaal at this moment. And it started with flash overheating mu GPU

Hello everyone,

We have two Imac 2010 mid with the same issu as everyone. As we knowledge apple doesn't respond to the problem. WE did send one imac to get check and apple said that everything was fine but the problem persist. I think it is time to take a lawsuit again the problem for the price we paid for our machine.

By the way we did the apple hardware test the long one and no problems came out. We do think that the problem is more software than hardware.

I've had this problem since december 2013, it's only getting worse. Next week I'm going to my Apple Service Provider to exchange the graphics card. I'm tired of this ****.

Well, it took 7 months after baking, but my dots finally came back.

I'm going to try round two of baking in a couple of weeks and will report back.

Cheers!

After much lurking, I'm about to bake my HD4850 following richlove's method (many thanks btw!). Just a couple of questiions:

- Should the card be placed with the chips up or down? (There does not seem to be a consensus about it)

- Some of the white puffy stuff remained on the memory modules after removing the heatsink. Should I remove  the stuff before baking? If so, what product should I use to replace it?

Thanks!

I have a 2011 27 inch iMac with the same problem. I called the apple store and he had me do a key combination to reset the video on boot up.

He said the community was crazy for baking the video card and they will replace the video card at my expense if that didn't work.

He can thinks what he wants.  All due respect but at the end of the day he's a step up from the best buy geek squad guys.  And that's ok.  There is actual science happening here, and this does work.  This is not something unique to Apple.  And infant these ATI Radon cards had similar issues in non-apple products. 

Apple will replace the card at your cost.  Ofcourse they will.  But if you didn't have to pay apple to do it wouldn't you be better off?  You can buy working graphics cards on eBay too.  This is a last ditch effort before doing that.

I Got Apple to replace the card, as others have, and paid them to do it. That card simply went bad shortly after a period of time.

SInce the card is a Radeon, but uniquse to the iMac, it's not that easy to find, and I found cheaper to buy from Apple.

All that said, baking is the only thing that seems to work reliably, including getting Apple to replace it.

Cheers!