Red and green square dots?

I'll order up those giant suction cups and follow the iFixit guide once things get worse. The fix is so hilarious and bizarre to me that I look forward to doing it.

6th day out from my "cook" and things are working great.

I would second the recommendation earlier not to disconnect the GPU connector from the back of the motherboard. Very tight and hard to get to connection. I left it intact. Not an issue.

I was able to pull the screen off without the suction cups, just slowly and carefully with my fingernails. Again, its just on with magnets.

Follow the guidelines online and make sure the card is up on something like the wadded up tinfoil balls like seen online.

Go very very slowly as you take things apart. Lots of little things to break.

For the rest of you, I tried all the tricks on here, but in the end, I have to agree that this is a HARDWARE issue and no software fixes are really going to resolve anything long term.

Hi everyone, I'm back again after many happy months of working graphics, but as temperatures dropped everything came back.

Back in april I removed the 5750, applied new paste, and made some attempt at reflow with a heat gun. I was too afraid to put the poor thing in the toaster oven.

My iMac was good as new for nearly six months!

As temps fell the squares started to return, but without crashing. Then I installed Yosemite. Worked well for a day, then one more cold night and I would see the worst I've ever seen in the many years I experienced this problem! The computer would hard crash within a minute or two of starting up, over and over.

Now that I have your attention, just a few hours after that photo, my iMac is back to good as new! As it was now rendered completely useless, I had more confidence and determination than ever to stick the graphics card in the toaster oven. Plus practice means I had everything out in less than an hour.

Five minutes at 450. Good for pizza. Good for Radeon.

We'll see if I get another six months, but it sure beats spending $350 on a new card that probably will still have the same issue! Apple, feel free to donate a new 5K iMac four my years of trouble with this!

I should say, months or years spent wondering if this was a software, kernel, driver, or even card connector issue. It is definitely a cold solder joint issue, which gets worse with time and low temperatures, and reflow is the only answer!

Hi all - I'm having the same issue with mine after upgrading to Yosemite (it presented itself a little bit in Mavericks as well), so I have a lot of info to weed through here. Just letting everyone know there's one more mid-2010 i7 iMac with the ATI Radeon HD 5750 1024 MB graphics card having issues. Will continue to monitor the thread for progress, and hopefully I won't have to bake my card!

Yosemite might give us the last glimmer of hope that Apple might do something about this. Not only is it pushing many more imacs over the edge, it appears it is able to recognize the graphics issue and reports it to apple. Of course, these machines are four years old, so they don't have to care. (It is clearly AMD's manufacturing issue anyway)

If there is interest I would be happy to write up the full process and post on my web site. I have photos of most of it.

If you have plunger, you can use that to remove the screen. I have removed my screen several times using only a plunger but I dare say I could use my fingernails as suggested by KirkB.

If you have the time and don't mind, a writeup would be great. I've ignored this issue, which has honestly been minimal, until the upgrade to Yosemite so I'm on the start of my journey here. To see what happened, the process you went through, and what worked/didn't work is certainly of interest to everyone having the problem. Thanks!

Josh, that would be very much appreciated - thanks!

Warming up the work area did help. Usually every morning I find my computer with the flickering pixels and I have to restart. I'm sure this is only temporary but it does prove to me it is cold solder joints. I will be definitely baking my card in the near future as well as replacing the hard drive with a SSD to give this computer new life.

A thorough guide with pictures on how to bake would be much appreciated. I know when I do it I will film the process for YouTube as I spent almost $600 at the Apple Store last year replacing the logic board and video card because the Geniuses couldn't figure it out. I'm thankful to everyone in this thread.

I took my mid 2011 iMac (21.5) to the apple store and it failed a heat sensor test (the one on the processor). They had mentioned off handedly that it sucked in dust, so I asked them to attempt to open it and give it a thorough cleaning if it needed it. They did end up keeping it for a week, opened it and cleaned out "a lot" of dust and then ran it through diagnostic testing for a week and couldn't get the heat sensor to fail again and could not get the dots to reappear.

So, it may indeed be a heat issue caused by several different kinds of issues. Mine was simply a build up of dust.

There was no charge for having them clean my machine by the way.

I have a few tips after sucessfully baking my graphics card...

1. This might be obvious to most but be sure to separate the graphics card from the heat sink before baking.

2. Have some fresh thermal paste on hand before starting the job. The old thermal paste will be dried out.

I removed all of the old dried out paste using a putty knife and put new thermal paste back on the heat sink.

(after baking the graphics card).

3. Baking temperature and time.

I did some research on this and in general, solder starts to melt at 350 degrees F (Fahrenheit)

And solder becomes fluid at 450 degrees F

So I picked 390 degrees as the baking temperature for a kind of middle temp. I am guessing that is high enough to re-flow the solder without worrying about the solder dripping off of the board.

I just picked 7 minutes for the time because someone else suggested it.

4. When placing the graphics board in the pre-heated oven, make sure it is sitting on a baking pan (not just sitting on an open grill.

Use some sort of standoff to keep the board from touching the pan.

Some people use wadded up aluminum foil balls because the foil will not adhere to solder. I used four screws as standoffs because there are four handy holes in the board to insert the screws.

The idea is that you don't want the solder joints on the board to contact the metal baking pan.

5. After baking, turn off the oven and open the oven door to let the board cool back down.

I waited a couple of minutes before removing the board from the oven because you don't want to move it while the solder is still in a molten state.

That's all I can think of for now.

Unfortunately, I did not take pictures, so I will leave that up to others to do.

I know that sounds like a crazy thing to do but it actually works.

Rich

Someone posted this link about the class action suit against Apple for 2011 MBPs that have a similar issue of cold solder points. It seems like they deleted their message: http://www.macrumors.com/2014/10/28/macbook-pro-2011-graphics-lawsuit/

We should be in on that! I paid $600 to the Apple Store for a new video card and logic board that they said would fix it for it to happen again. Apple needs to get AMD/ATI to pay. Apparently, it's cause they are using "lead free" solder that's no good.

Lead is a nasty poison, the less of it there is the better.

I'm pro environment but I'm also pro consumer. Don't sell me a bad product and then resell it to me again without telling me the problem. I would've put that $600 towards another computer and most likely another Mac. Anyways, I don't expect too much to come out of this and will most likely end up baking my card.

So far so good cranking up the heat and paying attention of the temperatures though.

Had the same issues uninstalled Google chrome.. Problem is gone!