Q: Red and green square dots?

Just wanted to say THANK YOU to Richlove. his posts gave me the courage to open up my IMAC 27" mid 2010 and bake my graphics card as instructed at 390f or about 200c for 7 mins.  I am no computer repair geek, but followed the instruction to the letter, NO MORE RED AND GREEN FLASHING SQUARES. YAY.

Only small problem is a couple of screws left over thanks to the magnets around the LCD i couldn't get them back.

After months of dormancy, my "shimmering spectres/dancing pixels" are back - with a vengeance! Must have something to do with the advent of summer weather, here?

I want to add myself to the list of people with small square dot display issues on a 27" mid 2010 iMac. Finally got frustrated enough to have Apple replace the video card (just under $300). Seemed good for a couple of days, then last night there were 4 static square dots on my auxiliary screen. Dragged a window over them and they vanished, and haven't re-occured.

Just found this thread today and read thru the first 6 or 7 pages (not realizing there were 36 pages total).

My computer (mid 2011 21.5" iMac running Yosemite 10.10.5) was flashing the square dots every once in a while, but recently became unbearable (probably after the most recent Yosemite update).   It does not look like Apple has this as a repair/recall item for the 21.5" iMac (only the 27"). 

I went into System Preferences>Accessibility>Display and selected "Reduce transparency"

It has eliminated 99% of the problem (at least for the past 3 days)

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.