Q: Red and green square dots?

I too have had this issue for over 6 months.  I have taken it to Apple and after a week they said there was nothing wrong with the machine.  Really disappointed the problem persists.  It is such a ghost in the machine, it will happen for a couple of days and then go away for a couple of weeks.  Recently mine got worse after installing the new version of Parallels (V.10.0.2). 

I have changed the power settings a million different times, unplugged items, turned off Time Machine.  The problem only happens when I wake the machine from overnight.  Maybe the pixel ferries get all crazy in my machine at night? 

"The thing i think is the problem, is a bad manufacture and a soldering problem, so, when it is cold, the parts retracts and this soldering get with contacts problem. But when it is hot,  the things expand because, and then this bad soldering keep connected."

Yes, I think you are right. I had a terrible problem with dots all over the screen that got worse when dragging windows around.

I have a mid 2010 iMac 27"

Have had this problem for a year or so but it just got much worse in the past few days.

I had thought all of this time that the problem was too much heat. So I have been using SSD Fan Control to increase my hard drive fan speed.

(the hard drive fan affects the graphic card temperature also)

But I just discovered today that the problem is really that the graphics card needs MORE heat.

My dots went away when I reduced the hard drive fan speed back down to 1200 RPM.

( I had been running that fan at 2200 RPM and my GPU temperature was 90 degrees F)

With the new speed of 1200 RPM, my GPU temperature is now 140 degrees F and it is happy.

After reading many posts in this thread, I will probably try the graphics card baking and thermal compound.

But for now the fan speed did the trick.

Rich

I still had some random dots appearing on the screen.

So I took the graphics card out and scraped all of the old thermal compound off and applied new compound.

Re-installed the card but it did not change a thing. Still got random dots.

So I took the card back out and removed the heat sink and baked the card in the oven at 390 degrees for seven minutes.

So far that seems to be the fix. No more dots.

Rich

So......here's an interesting development.....

I posted a little while ago that I had the red green dot problem, and had taken it to the Apple store to get the graphics card changed, which didn't help. I still have the problem on my iMac.

So, now I have the red green dots on a second computer. ......my Windows 8 machine! Looks basically identical to what I'm seeing on the iMac, and that Window's machine is running, you guessed it, an ATI Radeon 5000 series card.

Sigh.....

I don't know what Apple is doing when they replace your graphics board and it still has the same problem.

Are they installing boards that have cycled through the system as returned and repaired boards?

I had intermittent dots on the screen for the past year.

It had recently become so bad that the dots were all over the screen and would not go away.

It was also causing my iMac to freeze and require a reboot.

I baked my graphics board in the oven at 390 degrees F for 7 minutes and it fixed the problem.

It has been flawless for a week now.

An update.

It seems that although I thought I did enough to keep the machine turned on I did not turn off all the "hibernate" type functions, so sure enough the issue came back; actually a lot worse as I could not even get the iMac to start up (unless in Safe mode).

I found an app (free on the app store) No Sleep and installed it (in Safe mode with pink lines). I left the iMac running over night. Then the next morning rebooted, hoping that the heat would be enough to enable a start up not in Safe mode.

Unfortunately I still had the pink lines and could not get the boot up past the logo.

I decided to just let the iMAC sit there for a while at the logo with the "wheel" spinning. The pink lines went away after an hour or so- but never booted up.

So I rebooted but unfortunately the first reboot after the lines going away I still could not get past the logo (now with no pink lines though).

Second reboot however I got in, no longer in Safe mode.

It has been 3 days now and no lines/ green dots - the No Sleep app is keeping the machine on 24x7.

To me this really seems to show this is a heat issue i.e you need the heat on.

I installed the app Mac Fan Control (from the web) to have a look. My stats (with no pink lines/ green spots) are;

CPU Core 0 = 43

CPU Core 1 = 42

CPU Diode = 66

CPU Heatsink =63

CCD Proximity = 37

Mem Controller = 47

Unfortunately I did not install this when I had the pink lines/ green dots to compare the heat but for others it may be worth looking at your heat levels?

Of course this is a poor answer as I don't really what to run the machine 24x7. But not sure I want to fork out for a new something, and are not really confident enough to "bake" as others have.

Another update......

The graphics card Apple installed got worse and worse. It got to the point where it always had dots, hot or cold, and would only run for a few minutes before hanging.

SInce I figured I was probably going to have to replace the computer, I thought I would try the flow fix to see if it did anything. I took it apart and did as Richlove suggested, 390 degrees for 7 minutes..

It's been over a week now, no crashes, and not a single dot. Keep in mind this was on the "new" graphics card Apple installed.  I don't know if the flow thing is the only cause, but certainly seemed to fix it for me!

Cheers!

Much like everyone else on this post, I have been dealing with the pink and green squares for roughly 9 months now. I've gotten used to coming home and waking my display (hard disks do not sleep) and setting a screen saver (bright pictures) to run after 30 minutes with the brightness on high to heat up my iMac (mid 2010 27" i7 quadcore). After about an hour or so, I can use the machine without it freezing with the occasional blinking squares dancing across the screen. I've tried every trick listed on here to try and fix the issue (clean reinstall, pram reset, smc reset) aside from taking the system apart and baking the graphics card.

To my luck, I was messing around with resetting the SMC again and held onto the power button while plugging in and ended up making all of the fans come on at full speed. iMac: Fans run at full speed after computer turns on

Not sure why, but the system seems to run perfectly without any blinking squares or freezing. I've tested Steam, 1080p video and everything else I can imagine that would make the system hang up and it appears to be working perfectly (apart from the fans running at full blast). I've tried to lower the fan speed using the app "Macs Fan Control" and it tells me there is an error reading the setting and I am unable to control anything (it works after a normal reboot).  

Once, I reset the SMC to make the system run "normally" again, I get the blinking squares and the system freezes almost immediately after the system finishes booting from the SMC reset.

Take what you will from the post, but if you can deal with the fans running at full blast you might be able to find life after this issue without needing to bake your GPU.

Really hoping that Apple addresses this issue. I've had nothing but problems (also had a secondary display wake issue, but that no longer applies since I can't even use a secondary display without the system freezing).

You can add me to the list. I have an iMac 21.5, mid 2011 with the 6770M, and 10.9.5. Glad its not just me.

this is the temps today early morning!! (for my mac just wake him)

I have this problem as well on an 21.5 iMac mid 2011.  I think I found the cause - I run a program called Macs Fan Control and if the GPU Heatsink goes below 45 degrees C the flashing starts and if I turn on the fan to full blast, once it hits 32 degrees C it really flashes and then freezes.  If I run a GPU stress test program that draws a 3D video motion and heat the GPU up to above 60 degrees it is stable.  Will be taking it in for applecare tomorrow.  I think this all points to a video card problem. Seems to align with the comments that people are making that baking the board seems to fix it.  I think there is bad solder connections and when the temp gets too cold the contacts contract causing glitchy behavior.  When warm they expand and are better.

Yes, you are correct. the dots go away or are not as bad when the GPU gets hotter.

Cold solder joints on the graphics board are the problem.

It has been over two weeks since I baked my graphics board and have not seen one dot.

It definitely is the fix.

Took my mac to the applestore and the the heat sensor on the processor failed their diagnostic tests. They were going to open it up and clean it and restest. I'm getting it back tomorrow and will update then. They attempted to rationalize a free repair but were unable to find and open recalls for the mid 2011 imac, i5 or intergrated graphics card.

Just got my iMac 21.5" Mid 2011 back - they replaced the graphics card and it is working great again.  I left it off all night, turned it on in the morning and no pixelation or flashing.

Do you have a good walkthrough you have found for removing the graphics card with minimal fuss.  I always seem to remove more stuff than I really had to.  The ifixit.com one has very little on the graphics card for some reason.

Still doing good after the bake?