Q: Imac display issues following Yosemite upgrade

I see you have a 2013 iMac. Coloured square dots and crashes seem problem with iMac 2010 and 2011 with AMD Radeon HD 6750M and alike card in MacBook Pro and iMac.

I check the temperature too, and never had over heating. I use iStat widget to monitoring the GPU heatsink and Techtool Pro to have diagnostic of whole system. For example, a few minutes ago, an HD video running to keep the GPU hot, I pasted the result "à la fin" of this post. As you can see, temperatures are in the normal range.

I think you are a lucky one :-) to have a problem you can resolve. Probably not the same as mine, unfortunately.

One more thing, as I replaced the original drive of 500 GB, there is no more thermal probe, so I installed "HDD Fan Control" to control the ventilator. It works fine.

Merci to share your observation. But I continue to think of a AMD pizza :-)

Alex

From Techtool Pro "Sensor test" ;

Ambient Incoming Air  26.73 °C

CPU Heatsink  46.88 °C

CPU Proximity  50.88 °C

CPU Proximity 0  50.88 °C

GPU Die  61.00 °C

GPU Heatsink  59.75 °C

Hard Disk Proximity  9.00 °C

LCD Proximity  42.28 °C

LCD Thermal Compensation  42.83 °C

LCD Proximity 0  54.94 °C

LCD Thermal Compensation 1  44.14 °C

Optical Drive Proximity  46.00 °C

Platform Controller Hub Die  61.00 °C

Skin Upper Right  43.25 °C

Skin Upper Left  44.25 °C

Main Logic Board Proximity  56.62 °C

Power Board Proximity  68.12 °C

Power Secondary Heatsink  79.62 °C

Power Primary Heatsink  59.25 °C

Hi dear Anticoste...Your temps looks normal for Apple machine...A little high to power supplies but is not problem i guess...

you dont know how much i spend for a brand new machine that it supposed to work at least 5 years without problem..Anyway...Apple operating system...best.

Also you have Amd which is more difficult to have a problem...

As for the temp sensor for HD...Did you checked Owc? it have a kit for this reason but HD fan control is nice..

If you are sure about pizza then ok..but i dont know if you tried to reset nvram,smc,,,and last if is easy for you i think you must go for El capitan... clean install but must have a back up of your personal files...

I did a test before and i noticed with yosemite the screen problems where much more.Last i dont remember what else i did and the pixel problem reduced ..if i will remember i will post it...

But at me the main problem was high temps...

I have a feeling that even if your temps look somehow ok ...this is the problem...  Try to run your computer under the coldest situation you can (maybe with a/c on) and look if appear again...:)

The problem discussed here is for iMac 2010-2011. There is a replacement program for a similar issue with 27 inches AMD Radeon HD 6970M and some MacBook, but not for the AMD Radeon HD 6750M in 21,5 inches like mine. One can reasonably believe that it is connected to the card and that the passage in a pizza oven solves, for a time, this issue.

You don't have the same card nor the same problem. Quite the opposite in fact ! When my iMac is cold, it has frequent freezing, it's why I test the GPU warming with video non-stop, and it's seems to work.  One can never be 100% sure of the cause, but it appears to me that this remedy functions !

I think I've try all the tricks posted here in the 150 comments and there ;  Red and green square dots?  almost 600 comments !!! It's why I will try in fine the oven trick. I think you have the same apparent problem as a lot of people here, but not for the same cause... You are lucky ! Chanceux ! ¡Afortunado!

Alex

Yes i know that you talking about different model and the discussion is not for 27 inches...But it looks that this problem is not related to model or graphic card brand.As you can see the problem is at any mac...i would not do the oven because as i see people that they did that they had again same issue...i think is not hardware by the mean of soldering...except if you used it for a long time under overheating   and then GPU affected...Anyway i wishing you to find what is wrong.. i believe that is because of operating system ..sometimes thi can happen also of hard disk dying...

here my friend are my temps after the fix i made,after a heavy usage load...with cpu working at 50% and going to standby..

I continue to believe that you do not have the same problem as the AMD Radeon in the iMac 2010 and 2011.

I observe and test and try for 5-6 months now, beginning on Yosemite, and El Capitan Beta and now official release. I am now convinced at 90% that it occurs when the card is too cold ! Not too hot as in your case.

For maybe two weeks now I didn't have coloured square dots. I will stop to warm the graphic card for a while, to document if they will return...

I post a pretty picture of these sympathetic dots…

Salut !

Yes...my problem was exactly the same as your screenshot, but more and more tiny than yours and growing (Edited sorry:)and if i was opening a finder window that moment and moving it around the screen.. it was producing more areas with dots and at random square areas.

Have you tried one fix people suggested? i dont remember where , i saw it when i was searching to solve that...

System prefs>Accessibility>choose display at left and at right uncheck reduce trasparency if not already...

Another fix was very strange..but just boot to safe mode. and allow your machine there for a while and then go back to normal...

Hello Heli !

Yes I've tried the "uncheck reduce transparency" but I didn't see the safe mode trick. I'll try this for sure.

Merci !

Also i found somewhere an AMD official fix for this problem for macs but sorry..i searched again now and i cant find it....  (:

i fall on it even if i have Nvidia...i think i have seen the link at one games forum...people there they were complaining for this problem...as to Adobe forums too.

Again i dont think that is hardware problem...and more when you have that when is in cold situations.

Silly..i suppose you already did a repair disk and permissions at normal boot of course...

if i will remember something else i will post it..

Again,maybe you must do a clean install of El Capitan.If you have the full recovery mode.(you know,alt at boot)

If not look how to erase hard drive and do a clean install. Apple have an article for this somewhere...

Anyway ..be well and i hope you will fix it...

It seems to me that it is well a question of temperature of the graphic card. For 3 weeks, at the morning when opening my iMac I have almost always noted squares of colours.

Rather than to start to use it, I do what I’ve found on this forum ; I open a HD video on VLC and I make it turn in loop. Temperature GPU heathsink climb from 40 C to approximately 60 C degrees. I almost never had squares of color nor of freezing while thus acting.

It is not a rock solid proof, but it’s an important indication that at high temperature my AMD Radeon HD 6750M card functions about correctly. A little bit ”chiant” but less than freezes and freezes...

I maintain thus that your problem is not the same one as for much of users on this forum Heli A. But if you can find information about AMD official fix, I (and others) will be very pleased :-)

Salut !

Ok..i remembered one....Was before 2 months ..Google history saved me...

here one :

https://discussions.apple.com/thread/119178?tstart=0

Anyway i hope helps.....

Search also for cinebench test

Gpu test ( www.geeks3d.com)

novabench

Hi all, I'm having the same display issue and am currently unable to work. I've ran the script that Linc so kindly posted above and will post the results below:

http://www.pastebin.com/embed_iframe/R5ATQcz1

<iframe src="//pastebin.com/embed_iframe/R5ATQcz1" style="border:none;width:100%"></iframe>

<script src="//pastebin.com/embed_js/R5ATQcz1"></script>

I wondered if anyone can see what this issue is and suggest how I can get back up and running again.

Any help would be great.

Many thanks,

Devs.

You might want to consider starting a new discussion. Since this one is a couple of years old, less people are likely to look at it. A new post would be much more visible. You can link to this one.

Sure thanks and have done that also here: Imac display issues following Yosemite upgrade

I was hoping that some of the original posters would be notified and able to help.

Hopefully someone will chime in soon.

Thanks.