Red and green square dots?

Your explanation fits with the latest dotting of my screen.

Waking up my iMac to lots of dots. I have seen i many times before but ignore it until today when the dots coveres a third of the screen random places. Restart did not help.

But now that my Mac is warm the dots are gone.

I hope it does not get worse. Baking will take the price as my most difficult repair should I go there.

Wow, I did not keep up with this issue. I have a 2010 Imac I5. I had no idea there were so many responses. I will share my story, but have not looked at all of the posts. On Mountain Lion I did not have a problem. My graphics went bad in 2013, and Apple replaced the logic board. I didn't notice an issue until upgrading to Mountaineer. The dots were so bad I tried going back to Mountain Lion with a fresh install. This fixed almost my whole problem. I still get the dots, but it's rare and easily manageable. Thanks everyone for this thread. I will change my sleep settings right away. I need to read every line. I can't believe it, close to 100,000 views wow...

I can't believe it. All I did was back the resolution down to 1920x1080. Not one pixel issue this evening. Not a scientific test but wow...Has anyone tried just lowering the resolution slightly that has this problem?

Sorry to hear your squares came back.

My bake has fixed the problem since Dec 20, 2014. Almost 9 months.

I've successfully upgraded to Yosemite and El Capitan Beta and neither upgrade caused any issues.

I thought the word "bake" was a typo. I looked it up and evidently it's not 😁

I opened the Imac to install two SSD's and a 4TB and swore I would never do it again. Installing that first SSD by taking everything out of the Imac case was for me, a killer. I've built many computers, but this Imac is so easy to accidentally break something...oh well...😟

Looks like I might have to...at the very least, I'm sure it can use a good cleaning. Who would of thought baking a viideo card could fix this problem.

https://macman860.wordpress.com/2013/02/03/baking-a-graphics-card/

This is the exact problem I am experiencing on my late 2012 iMac 21.5" (NVIDIA GeForce GT 650M 512MB-graphics) - pixelated red,green dots, computer freezes and all I can do is shut down. So frustrating - I love my mac for its format in working with all of my design/art programs but this has become so ridiculous. Its my 3rd iMac, the last one lasted around 6 years before the power supply died and now this one only 2-3 before problems have arisen.

First of all, iMac isn't meant to be used for severe usage. Not enough ventilation for stressed out condition. Despite that, it it runs 3-5 years! It is actually not bad at all.

I agree...it was one of Apple's first attempts to solder video on to a logic board. That is always a cause for possible issues.

I am having the same issue too.

OS X Yosemite

iMac 27 inch mid-2010

Processor 2.8 GHz Intel Core i5

Memory 16 GB 1333 mHz DDR3

Graphics ATi Radeon HD 5750 1024 MB

I have the same problem here 😟

Well actually the solution is very simple. I use an eraser and cleaned all pins of the RAM with it. No need to press too much but gently remove top coating of all pads. Working like a charm and all symptoms I had before disappear.

You have the same machine as I - except I'm at 32Gb of RAM

Finally capitulated and baked my 5750 card today...which appears to have resolved the video/graphics issues (as no pixel have reappeared) - but my machine won't restart.

Truth-be-told, it had become progressively harder to run - due to the video problems - and got to the point where I couldn't restart it. Assuming it was due to the video card issue, I finally baked this afternoon. Now - restarting in repair mode - it initially refused to recognize the 2TB main drive, only finding the eDrive... when I tried to reinstall system software.

Finally able to identify and assign the main HD as the start-up disk, but when restarting it refuses to accept the command-R directive and enter repair mode.

Suggestions?

Possible to connect with another of my iMac's and restart in "target" mode to run utilities from that iMac?

TechTool Pro 8 has been running for over 24 hours on the OEM Seagate hard drive: 670,000 blocks (out of over 3 trillion) and more than 7,000 report "bad".

Hopefully, I'll be able to recover data and files, but it appears the drive itself is beyond salvation. Seagate 4Tb replacement en route.

Can't help but believe the HD 5750 graphics card problem exacerbated and accelerated this hard drive failure...

Good news is the graphics card issue seems to have been rectified by "the bake" (thank you - richloveOct 23, 2014 10:27 AM , from page 29 of this thread)!

I have had this problem on 2 x iMac's (27-inch, Mid 2011).

The problem on both has been determined to be the graphics card.

Apple has a replacement program, so even if you are out of warranty, you can get your mac fixed by Apple for free.

http://9to5mac.com/2013/08/16/apple-opens-graphics-card-replacement-program-for- some-mid-2011-imacs/

I wish this included the 2010 model.