Red and green square dots?

OMG I think after 4 months of struggling with this and freezes 5 times a day, it is fixed!

I have a 2010 iMac here at work. This started about 4 months ago and has gotten progressively worse. I even have a chart next to my desk with a photo of my two monitors that looks like a picasso painting where I keep track of lost time and reboots...

I did the following, but I am pretty sure step 2 fixed it.

Went into Accessibility preferences and clicked Use Grayscale. At that point they stopped. But I can't have grayscale, so I removed that option, and then clicked the Reduce Transparency. That seemed to do it for real. So

Someone else had mentioned that in this thread somewhere but I was unable to find the option.

Uh Oh... Nevermind. When I opened my mail just now a few of the pink boxes showed up. But it is clearly 99% better. There are certain apps where I got it every time and they are not appearing with them right now. At least I can work.

I'll reply with an update at end of day.

Stay tuned...

And for kicks, here's my picasso that eventually evolved from the pink and green boxes.

So far only a few boxes now on my secondary monitor.

To raise the internal temp on an iMac, you can put some tape over the ventilation slot on the back of the machine. Try just a few inches at a time until you get the temp you want. This could lead to overheating if you later want to do some heavy video. Blue masking tape is easily removed, so I'd go with that as a temporary fix.

I also have the random squares (8x8 pixels) popping up at random, on my 27" mid-2011 iMac, running High Sierra (OS 10.13). (Seems to me the 27" model is over-represented on this thread.) Their appearance depends on the color of whatever they're laid over - e.g., all my yellow disk icons have red pixels, all the grey portions get magenta or multi-color pixels.

As others have noted, they're erasable by dragging a selection rectangle around them with the cursor. I have an external monitor (LG flat screen) and the little buggers appear there as well. I think it's clearly a hardware issue - these things are originating in the GPU, and get sent to both the built-in and remote monitors.

My GPU is running around 120ºF. I'll have to experiment to see if there's any correlation with the appearance of the squares.

I agree with your rebuttal, Anticoste. I am having the same problems stated throughout this 41 page thread regarding the random, flickering little pixel blocks. I'm on an iMac (27", Mid-2011); 2.7 GHz i5; 8GB 1333 DDR3; AMD Radeon HD 6770M 512MB; Yosemite 10.10.5. Being an "Apple issue", they should do better protecting the interests of their "valued customers" and help to resolve this issue rather than turn their backs and leave us struggling with their defects. Regardless, thanks again for defending old threads for those of us on older Macs, seeking information. I just came across this thread now, 5 years later. I am not alone in this longstanding issue. I will try the "reduce transparency" workaround and see if that brings any relief. Shame on you, Apple!

Hello. Old discussion can be useful ! We aggree 😀

OK, for the tricks ; none have done the job for me (iMac 21,5 late 2011, AMD Radeon HD 6750M) but...

But recently I've format my iMac to sell on eBay, downgrading to OS X 10.9 for the test and you know what ?

Not one %#$! square dot and no more freeze in more than one month ! Arghh 😠

So, I don't know exactly where and why this problem really is, but it's possible there is a flaw in AMD card, combined with some new OS X functions...

Les voies de l'informatique sont impénétrables 😝

Suerte !

I recently updated my mid 2011 27" iMac (2.7 GHz Intel Core i5, 32GB 1333 MHz DDR3) to Mavericks about 3-weeks ago. Last week, the entire system shut down seemingly at random while using different programs (it even shut down while using system preferences at one point). I decided that I would do an entire fresh install of Mavericks. It took several tries to be able to erase the drive and install a new OS (created a boot installer, connected it to another computer via thunderbolt). After I finally got it up and running, I started installing new programs and testing things out.

As I have been running new programs, I've noticed the exact same behavior with the dots, which I never had previously. The computer has randomly shut down a few times, and I've noticed it happens when I tax it too much and try to do too many things at once. As chaddaniels noted, if I move a window over the pixels, they go away.

I was afraid it might be a hardware problem that is causing the issues I've been experiencing. Could all of this be the result of a failing graphics card?

This happens to my iMac 27" mid 2010. I think this is definitely a thermal problem for the GPU, and here is my workaround to avoid those color squares.

Download a fan control software for iMac, for example Fan Control. Control the temperature of GPU to be above 50 degrees C and those squares should go away, this works very well for my Mac. I tested this also by letting fans work at max power, GPU temperature drops to 40C and those squares are back again.

Good luck guys!

I would echo several of the earlier comments - that for many (including me), this must be caused by bad solder joints.

On my 2011 Imac, I first tried all of the "settings" type of solutions mentioned in the thread and none worked.

I then installed mac fan control. I monitored for a few weeks and realized that I would only see the dots or anomalies when the GPU temp was below 130 deg F (54c). To keep the temps on my machine up, I have had to resort to having numerous browser windows open which stream video constantly. If I don't do that, the temps fall, the dots reappear, and the computer may crash.

This has been going on for the past 10-12 months and I have duplicated this behavior dozens of times.

To further reinforce this hypotheses, the problem only really started happening in earnest, immediately after I replaced the crashed mechanical hard drive with an SSD which cooled the internal operating temps significantly.

It's gotten bad enough, that I've tried to adjust the fan operating using the program but it doesn't seem to help. The machine runs so cool now the hard drive fan never runs, and even with the CPU & smart drive fans idling, I have trouble keeping the temp above 130deg F.

Having 4-5 windows open streaming the video is a real pain. Eventually the video queue ends and needs to be manually restarted. With that many browsers going I need to check every few hours. If anyone has any ideas on how to keep the internal temp on the machine up without doing this please let me know!!?

All in all this is extremely discouraging. My first Imac lasted 5 years and died due to the bad caps issue. This replacement also seems to have a 5 year life span. Disassembling and baking the motherboard seems to be temporary repair at best though it may come to that. One thing is nearly certain, I can't see myself replacing this machine with another Apple product.

Meanwhile, I have two 10+ year old PC's in the basement that still run fine...

Hey, thanks jp, great idea, I will give that a try.

On my display, I see very small flashing, mainly red, dots randomly appearing all over the screen...they almost appear to vibrate. I suppose the symptoms depending on the exact circuit path where the solder is failing.

Hope it works for you. And I now agree that it's temperature-dependent. When my iMac has been sleeping for a while, the litle 8x8 spots are flashing all over the place (they travel in packs, flashing in unison). When the GPU diode gets to about 125ºF, they're gone. Starting cold, after being shut down overnight (something I don't do unless going out of town for a while), the whole screen is a flashing mess. People with SSDs see this problem more often because the internal temps on their machines are cooler.

I've set Macs Fan Control to run the CPU fan on the basis of the GPU diode temp - the fan kicks in at 125ºF, and maxes out at 140ºF. I still see a few spots first thing in the morning, but they go away after about half an hour of use. Remains to be seen if this is a long-term fix, of if the solder joints will continue to degrade. Thermal cycling is the usual culprit, so minimizing total shut-downs is a key strategy. If it gets worse I'll have to rip the thing open and do the solder re-flow thing; maybe I'll re-solder a display connector while I'm at it (there's a notorious bad solder joint on a specific connector that causes the lower-left corner of the screen to be dim.)

I also monitor the GPU diode.

At first, below 125 degrees was the temp where I would start seeing problems, then 130 degrees, but unfortunately has been getting higher and higher during the past 10-12 months.

Yesterday my machine was off when I got home (crashed I guess). I partially taped the rear vent, re-booted it and it took about 30 minutes to get GPU back to 130-140 degrees. Little 1/4" green, red, violet, and yellow squares dancing all over the screen the entire time. For a solid half hour the GPU diode temp was 150 and I still had the problem.

Then the screen went blank again like it shut down. After I pressed the power button it acted like it was waking up from sleep as I didn't have to log in again and all windows were still open. I then decided to put in a DVD and that really helped warm things up. Finally, after a couple hours, I got it in the 155 degree area and the colors went away.

Does anyone know what the safe operating range is for the CPU's? I have a quad core and the CPU heatsink was also in the 150's with the CPU fan ramping up a bit when I finally got the dots to go away. I'd obviously like to adjust that fan to run as little as possible while still maintaining a safe operating temp.

Well, you can bake at 375-400ºF when doing the re-flow, so I'd say the physical limit is pretty high. Don't think you want to get the rest of the Mac's innards to that point, which rules out doing a re-flow in situ. (That rattling sound you hear is surface-mounted components falling off the boards as their solder melts!) 200ºF is common for processors hard at work, and in any event the Mac OS keeps an eye on these sensors and will throttle or down-clock the chips if things get out of range.

I just re-installed a program called BOINC, which I haven't run since I got the new iMac. It does scientific calculations on behalf of a distributed computing project - you get to pick a project, they send tasks to your computer, and your machine chugs along in the background doing the tasks, sending off results and getting new tasks autonomously.

https://boinc.berkeley.edu/

The thing that I remembered just last night is that you can set it to use your GPU for the computations. It will run 24/7 or on whatever schedule you set in the preferences. It got my GPU up to 130ºF in minutes, and eventually to 170ºF.

If things continue to deteriorate, at some point the OS limits will prevent you from getting to the temperatures you need, and baking will be the only option.

Thanks so much for the BOINC tip! I installed it and running the program has essentially stabilized my machine!

With BONINC running constantly, I am able to adjust the fans so that the GPU diode stays between 140-160. This is the best my computer has run in a year. Keeping my fingers crossed.

You referenced the HT4044 article covering pixel anomalies in your title, but the description sounds like an issue that is affecting a larger area of your display.

How big are the squares that appear on the display?

How long has the issue been occurring? Did you make any changes just prior to the issue occurring?

What version/build of Mac OS X are you running? Have you checked for software and firmware updates which can sometimes correct these types of issues?

Have you tried creating a new user to see if the issue goes away?

By any chance did you clone your data from another system to your iMac? If you did then you may have an incomplete version/build of Mac OS X that doesn't have the necessary kext files to support your graphics hardware. Reinstalling the OS may be worth considering.

Have you run the Apple Hardware Test to see if it generates any errors?

Can you post a picture showing the issue?