Red and green square dots?

Same here. A few weeks ago I changed energy saving to put my iMac to sleep instead of never sleeping and it's dissapeared.

After reading this thread I took my 2010 27" iMac into a local store in Boulder, CO, the Mac Shack. They are an authorized Apple repair center. They determined that my graphics card was bad and replaced it. Part was $250, total cost was just over $400. Things have been working well since then.

I am keeping my fingers crossed the problem doesn't reappear, as it seems to have for others on this forum.

Reinstalling everything, the problem returned so I tried this sequence:

1

Intel-based Macs: Resetting the System Management Controller (SMC)

http://support.apple.com/kb/HT3964

2

Resetting NVRAM / PRAM

http://support.apple.com/kb/HT1379

THIS WORKED FOR ME! 🙂

Hey All,

This started happening with my sons iMac11,1 with the 2.6Ghz i5 one week ago. By the third day it was freezing at the spinning gear and would only safeboot.

His Seagate was part of the recall and was done two years ago (before AppleCare ran out).

I'd been meaning to upgrade his system for about the same amount of time, but didn't get to it. The "the lines and blue squares with the gear freeze thingy" forced my hand.

So I just finished with an i7 870 brain transplant and a 5750 video upgrade, and ... voilà- it's fixed!

But I imagine everyone expected that. And yes, I'll get back if anything changes.

But I don't think it will. Here's why- it sounds like everyone has had about the same luck for about every supposed fix. Whether it was hard drive, re-installs, etc, etc...

"There is little to no common trail regarding this issue....

jmf"

Yeah... I'm not dead sure about that Jack- I think I did notice one. It's the one thing no one mentioned and that accounts for some of the most arcane of the Mac's weirdnesses I've seen over the last 25 years.

Is my solution the only one? Nope. And a lot of people would see improvements if they blew the dust of their heat sink fins, did re-flows, or reset the SMC and PRAM. Because y'all know as well as I do that a lot of the video cards and hard drives are a bit "twitchy" to start with. Not to mention the RAM.

So I knew that if I had to crack open the boy's iMac, I just may as well do the upgrades. They really don't cost that much when you realize your iMac will prolly be good for another 4-5 years. A modest expense now rather than a much bigger one with all the rest of the "off to college" expenses in a year.

So does everyone want know why I had to open the kid's iMac?

Simple.

The battery needed to be changed.

Hope it helps.

Wamest Regards,

Robert

Same problem here or should I say worse. My random dots span across dual monitors and take over both displays. The problem is worse in the mornings during a "cold" startup. Then seems to simmer down after the machine is warmed up, if you will. Almost like how a vehicle operates in the cold. Here is a picture of the issue in the worst state. A hard reboot is usually the only way to reduce the takeover, but the issue remains afterwards.

This is my third post about this problem, the last solutions worked only for a day 😟 but...

Today I updated to Mavericks 10.9.3 and the problem seems totally disappared

We'll see next days if it's really true.

So I've been following this thread from the beginning. I'm another schmuck with a 2010 27" iMac with this issue. Started off as just a few, occasional pink and green squares. However, with each OS update, it got worse. Mavericks made it intolerable where my machine locks up 2-3 times a day.

I too just updated to 10.9.3 and its been half a day with no signs of the problem. Hopefully its fixed finally. We will see.

WOW, you're right. Just when I was beginning to think we were being ignored, the issue is gone. A miracle so far. I got my Mac back.

I lied. Nothing is fixed and we are being ignored.

My iMac 27 mid 2011, with 6770 512mb, is with the same hardware problem here.

I say hardware problem, on the vídeo board, because it shows when i use more the video board, and it happens to on windows 7 boot.

Same color squares aleatory on screen. More when i use Adobes or Maya 3d.

On Games in Windows too. And other 3D discrepancies.

iMac, 27-Inch, Late 2009. Graphics ATI Radeon HD 4850 512 MB RAM

Applied OS X Update 10.9.3 today and now I am getting blue and pink squares. System then locks up and I have to reboot via power cycle. Has happend serveral times today, but has never happend since I got the machine over 4 years ago

Gray Apple Logo Startup screen some times has blue, pink and maybe some green lines and well as some squares. Had to use shift key after reboot to go into safe mode to get backup and running Ran disk util all was fine. Did normal reboot.

Screen shot of last lockup

Lock-ups continue.... Just postiong latest start up screen. Had to use safe boot to get around this.

Apple Hard Test - basic and extended pass with out probems

My iMac is still working a month after the video card was replaced by a local independent Mac store that is an Authorized Mac Repair Center.

When they were troubleshooting the issue, the problem was not detected by the Apple Hardware Tests, although it was very visible to the tech, as there were screen anomalies showing up even while running the tests.

I was skeptical about replacing the hardware, but so far it appears to have resolved my problem (knock on wood)!

3rd day after Mavericks update, still working.

(my boot screen was always perfect)