Red and green square dots?

baking the card at 200 C for 7 minutes and cleaning and renewing all the thermal paste seems to have done the trick. we'll se how it holds, but i have a feeling that this is it.

Hey Muzo, I have a mid 2011 iMac that's got green square dots that intermittently flash on and off. First, I tried taking a screenshot, and no dots show up in the resulting image. I then booted from an Ubuntu cd and still saw major graphic glitching, including the green dots. Then I used my macbook pro to use the iMac as a secondary monitor using Apple's "Target Display Mode", and this revealed a perfectly normal screen on the iMac with no graphic anomalies whatsoever. Finally, I sent the iMac's screen to my macbook through ScreenRecycler and VNC, and again, no green dots were transmitted. What I'm perplexed about is the fact that the monitor worked perfectly during "Target Display Mode". How can this be? If there were a graphics card issue, wouldn't the dots still show during "Target Display Mode?

Thanks for any help.

I am experiencing the red and green squares too, I just wanted to add, that I see it via Back to my Mac as well!

bests, Stefan

Guys do you have Google chrome installed? If so delete it, that should fix the issue.

John;

The presence of Chrome (latest iteration) hasn't affected my display issues one way or the other: Disabling transparency and defeating all energy saving settings has been the only salvation from the "dancing pixies"... but I've resigned myself to the conclusion that ultimately I'll simply have to remove and bake my board for anything approaching a "permanent" solution - pending the success of the recently filed class action lawsuit addressing this same issue as it pertains to MacBook Pro's (in which case - with any luck - Apple will research and resolve, then offer a complimentary fix?)....

I'm Going to share my exp.

My mac:

27" iMac late 2009 with AMD Radeon HD4850 512MB.

My problem:

Turn my pc on and 5 red veritcal lines showed on screen. Pc started loading and got stuck at apple logo and hundreds of mini squares appeared all over the screen. (at this point the red vertical lines disappear). So basically it wont boot.

The one way to boot was with Safe Boot. Safeboot showed the vertical lines but the colors changed depending on the background.

Using the mac in TDM (target display Mode) showed not a single lines or sqaure, flawless.

My solution:

I was using my imac as a very nice looking monitor for the last year, until yesterday I decided to bake my Graphics Card. I baked it at 190C for 6 minutes. Reassemble my mac and voila! working with no screen issues! Guys try this baking method if you are out of warranty.

I got my graphics card replaced for $400 and haven't had any issues since. With the class action lawsuit going on, there is clearly an issue with these cards over time.

Jeff;

Did you have the card replaced by Apple? What card - specifically - did they install, please?
Year/model of your iMac, please?

Thanks!

For what it's worth, after following this thread for the last few months with the same issues in disbelief that I'd need to resort to the reflow option to fix my computer's issues, I finally went the reflow route one week ago today. 7 1/2 minutes in a toaster oven at 375 degrees. Absolutely no issues since that time, and I've been running my energy savings settings on default. Incredibly unbelievable to me that customers are having to bake their GPU's to fix this issue. Apple can do better...

Hey, spent the past few days reading this chain on issues people are experiencing as I have had the same issue. I contacted Apple Support just as my machines warranty expired. The tech ran me thru a hard drive diagnostic where we discovered an issue with the HDD but a repair completed it. I was told that if it comes back it could be the HDD failing and if that was the case a reformat of it and clean install of the system would be needed. After I did the HDD repair it actually was not as bad until this past weekend.He didn't believe it was a graphics card issue at the time as every time I did screen capture the pixels would disappear and not come back. I did a time machine backup, wiped the HDD and reformatted then followed by a clean install with yosemite. For the first hour the machine seemed to be perfect with quick boot time and no real issues. After running for a bit the pixels came back and this time they came in force. After a hard reset I got a thing saying a graphics card issue was noticed and it reported it to Apple. I spent 6 hours on hold waiting for tech support to answer to no avail. I hung up, contacted Corp HQ and asked to speak to Customer relations. I spent an hour holding for that person. I explained the issue to this gentlemen and explained I did an AHT and was getting a 4MOT error but it did not appear to be HDD or HDD Fan. I also explained that I was able to screen capture the pixels so it pointed to hardware failure vs HDD having corruption issues. The re told me he would contact tech support and call me back in 15 minutes. An hour later I finally got a call back from him where he explained he sat on hold for an hour to have a 2 minute convo with tech who confirmed what I told hi it was. He informed me that the time was not fair to customers and seeing I have been dealing with this for a bit he gave me a code to repair my machine at no cost to me. He setup an appt at the local genius bar for me today to drop the machine off. I took it in today where they did further testing before booting the machine up. After all tests came back clean he booted to look at the console and my screen shots. The machine booted really quickly which he said it would not be my HDD failing as everything went smooth and 30 seconds later the system showed the pixels and froze completely. With that said he confirmed it was my graphics card and put it in the shop for repair. My suggestion to all who are having this issue is to read the posts about what is going on then call customer relations, not general support to tech support. Explain the issues you are having and point them in the direction of this forum. They will do everything in their power to fix the machine. I will update when I get my machine back in a few days and let you know what they discovered. Total pain in the butt but at least theydid the right thing and are covering the costs. Good luck to everyone.

Armedic;

What year and model - specifically - is your iMac, please?

And which specific Apple Store was your repair completed at?
This information would be most helpful to those of us who have to go the Customer Service route as you did (my nearest Apple Store is nearly 200 miles distant)...
Thanks!

What seems to have been the problem for me (and how I solved this red dot/green dot issue) was to remove Google Chrome.

Like many of you I'm running a 27" iMac from mid-2010, Mavericks, w/12 GB RAM.

For what it's worth, two weeks after finally resorting the toaster oven, my screen issues are still gone. Running Yosemite. Default energy savings settings. No more issues. Good luck to all in finding a solution that works for you... after paying for something that should have just worked in the first place. Ridiculous, Apple. I expected much better.

I do believe their egos are getting in the way of their efficiency.

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

hahahahaha