Q: Red and green square dots?

You are all right and wrong.

You are all lucky I will waste some time to settle this.

None of you know how things work, this is why the thread is hundreds of posts long, for a Thermal Failure Issue.

The graphics cards are failing due to inadequate cooling. This is not due to Radeon or AMDs designs it is the heatsink that is directly responsible.

Heat Sink.

CPU/GPU overheat why? Because of inadequate airflow, or inadequate heat sink capability.  Processors are responsible for rendering that image. That's why the pixelation and artifacts are related to mouse movement and input as well as images and programs.  Its rendering ERRORS related to thermal failure and they stack up in memory until it eats the Buffer and freezes the Processor.  See? Simple.

We know this because we are Old. We built machines with ISA, IDE, and Dipswitches using 8086 intel CPUs in 1989.  Or around there.  Whatever.

But I did read ALL your posts, for hours, because I really do care. Re-flowing a GPU. Just like fixing an Xbox or a HP laptop GPU on the MoBo is the same thing as described elsewhere here.  Dude its not the lead free solder. Calm down.

Started you all thinking though, drinking that AppleJuice and questioning the knowitall BS Geniuses.  Breathtaking arrogance to call them this. I know about breathtaking arrogance.

Apple engineered this failure and there are ONLY TWO reasons why this happened. Either the Heatsink is inadequate or the GPUs operating parameters are incorrect. Apple is totally liable for this, completely, as the system integrator and retailer of the complete system they have no right to fall back on AMD at the end users expense.  Apple should have recalled these units but there was NO economically feasible way to get out from under a HUGE failure with no easy fix.  Those cards are hard to find eh?  That's why redesigning the heatsink and recalling the PC would have been a disaster. Replacing that GPU with one that could function within the heatsinks ability to cool it would have fixed it.

Thermal paste and other mods MAY work after reflow.  Fancontrol utilities which can raise the GPU fan will also help. Presumably.

Blame Apple.  They deserve it and they are to blame. They make incredible things, but they F-up too but unlike us they will never take responsibility unless forced by law.

Well it seems the lead-free solder may actually be the culprit, placing the blame on AMD pretty squarely.  Manufactured defective and Apple is still liable as system builder and the ultimate end user sales channel.  Remember this when you jump up waving your iPhones in the PC guys faces. It's all the same in the end.

Hello everyone,

I'm having the same green/purple dots issue for several days now. The screen eventually turned to black or the iMac was not responsive anymore. I tried everything, from AHT, PRAM zapping, and so on. Nothing helped.
Until I stumbled upon these 4 command lines this morning. No more dots, my machine seems to be new again.

Hope it will last.

Here's the process.

1. Startup your Mac in single user mode, holding the command-S keys.

2. After the loading is done, type /sbin/mount -wu /

3. Wait till the previous command is finished and type /bin/chmod 1775 /

4. Type /bin/sync

5. Type exit

Credit : https://www.youtube.com/watch?v=qKOX72xNmbo

Hope this helps.

So did this fix the green/purple dots issue also?

For the past ten hours, not a single sign of green/purple dots on the screen and iMac works perfect.

I will post here if they come back.

Did you try the trick ?

I have not because my screen did not turn black and become unresponsive. The youtube video is to cure that not the little squares?

Originally, yes. I stumbled upon it after a single blue screen issue.

But it resolved also my green/purple dots issue, wich was my main problem.

Anyway, give it a try : you won't loose anything on your HD. And please leave some feedback.

Doesn't Work! problem started up immediately after restart.....

He's not having the same problem.  notice how he's calling it dots, not squares.  The problem you're having, if it's like the one I had is due to the solder breaks.  Reflowing should fix it.

"Reflowing should fix it."

What does this involve?

Removing the GPU card as described in the thread, and either using a heat gun or baking it in the oven as others have done.  I had this issue well over 2 years ago, and since I baked my GPU I have not had a re-occuranc of the squares or the crashes.  There is a risk involved in this, but you will hit a point where the computer becomes unusable. You can also find a replacement board on eBay.

I am talking about this kind of square/dots issue.

Since yesterday, I had again some random ghosty squares on the screen.

But nothing in comparison with the mess I had before.

I'm pretty sure that this issue is a software issue.

1. I have two connected 27'' mid 2010 iMacs and when mirroring my defect iMac to the other, everything seems fine : this excludes graphic card problems.

2. In some cases, the dots/squares are moving on screen while scrolling or have their reflexions in previews (see below) : this excludes monitor problems.

Anyway, I'd think twice before baking anything in the oven.

Fairly certain this is the same hardware issue everyone else had.  Mine when it first started could go days or even weeks without re-occurring.  Then it eventually got progressively worse.  since this is due to very tiny fractures in the solder your mileage may vary based on temperature/expansion etc.

So in thinking that this is a heat issue I upped my SMC Fan Control settings to a higher RPM and put the computer to sleep more frequently to cool things down a bit. Man was I wrong! Things got way worst. More artifacts, lines, portions of windows blank, crashes, etc. It turns out that you want your machine to run hot. The breaks in the solder expand the hotter the computer is so the GPU works better! Still have some problems but not as bad. Disable SMC Fan Control and do not put the computer to sleep!

Well Zatlap, you are wrong. Let us all know when you've fixed the software.  Whatever software that is.