Q: Imac display issues following Yosemite upgrade

I am having same problems - Pixelation of screen, strange video issues, and locking up of entire imac.

I have a 27 inch imac, late 2009 model

I have never had in issue that I couldn't resolve or wasn't user error on my part.  The imac made me a believer in apple products and operating system again.  This issue seems nasty and related to the Yosemite updates(s).  I wish there was more known about it and was resolved quicker and openly with Apple. 

For now I have turned off transparency and unplugged my peripherals.  It is working, for now.

Any further updates people have on this please post here or some type of link.  Thank you.

Transparency OFF did the trick for me.

Running iMac 27 mid 2011 12,2 Radeon 6770M 512

Been two days now, no lock ups or screen issues since turning off transparency.  I have also plugged back in most of my peripherals without issues.  I am going slow getting them back on to see if any cause issues. 

I spoke too soon... it just rebooted and came back with screen artifacts and lines down the screen. 

I too have this issue.  Can't believe how far the Apple has fallen   They really don't pay nearly as much attention to their customers as they used to.  Tried the "reduce transparency" option and waiting to see if that works

Given the number of updates, it's likely a very low number of people having the issue. Not saying that it shouldn't be solved it's just that it doesn't happen to a lot of people (yes I have seen the other threads).

That said,

after I had the issue and switched my screen resolution back and forth I didn't see the issue anymore, and yes I have transparency and all that on.

I have no idea why it doesn't happen anymore.

rvantwisk,

What do you mean by "switched my screen resolution back and forth"?

Thanks you

I went to System Preferences -> Displays.

The is a resolution option you can change for your display.

When I did see the blocks, I could still see my cursor and changed it to scaled and choose a different resolution. After switching to this new resolution I switched back right away to 'Best for Display'. Right away the block's where gone. I am guessing this result's the GPU driver's settings?

I also had similar success when I switched back and forth between my apple TV, also that changed my display resolution as I am using mirror mode...

Hope that helps..

I took my Mid-2011 iMac into an Apple Store to have this problem checked out. It was before I saw the posts about turning off transparency. They ran some diagnostics and said it pointed to a video card issue. I mentioned that others were having a similar problem but was told that it wasn't an official recall or anything like that. I figured I'd go ahead and replace the video card if for nothing else to know if it was truly a software or hardware issue or both.

I've now been running it for a few hours and it's working just fine with the new card. So, it seems like it's a combination of an old card that was failing (probably crappy solder as has been described on this thread) and Yosemite pushing it to the max. But with a new card and same settings all seems to be well. It cost $151 plus tax.

Same problem here. None of the posted fixes work. like others, my maching started acting up in Mavericks and then the squares went ballistic in Yosemite, with crashes. I'm going to call Apple Support but I know they are going to say, "I never heard about this problem before."

Class action lawsuits are a joke. The lawyers walk away with a few million, while each member of the class might get a $50 gift certificate to the Apple Store. How does that fix your Mac?

I've done all the suggested workarounds and will conclude that none of them are the longer term solution. I have a iMac 2009 27" with a souped up 4TB internal HD and 16 GB RAM.

The one solution that worked for me is the following

Update to Yosemite newest version

Reduce transparency

Change screen resolution to 1280x960 instead of highest (one notch lower)

After doing the above the pixelation has not returned for one week on the computer. I'm not sure if this was a fluke or something I did at random. But its worth a try until apple actually announces a fix for this.

This is the graphics card falling short

Same here.  iMac mid 2010 AND 24" Apple display with ATI graphics card - both with screen glitches .  More than display issues.  Random lockups after odd screen flashes - usually after a right click on desktop

Reinstall clean version of Maverick.  No issues.  Sorry but this pretty much puts the blame on Yosemite.

I think it's combination of a bad video card made worse by Yosemite. If you see my post above, I've now been running my 2011 iMac 27" for a week or so now with a new video card and have no problems at all anymore. It used to glitch a little with Mountain Lion and then was unusable with Yosemite. (I never went to Mavericks.) So, a graphics card issue arose at some point because everything used to work perfectly fine with Mountain Lion and then began to develop a few months ago. When I went to Yosemite, like I said, it was terrible. But now with the new video card, everything is fine. Therefore, I believe it's a failing video card plus a new operating system that must be pushing it beyond what it's capable of handling unless it's in perfect working condition.

That's one way to look at it.  I can confirm seeing occasional glitches in Mountain Lion and maybe fewer in Mavericks. Not scientific but both OS versions are usable. Yosemite locks up a couple of times a day for me, so it is definitely not usable.

I take the position that Apple is not testing against the actual iMac hardware that was sold in mid 2010.  They probably have a few test systems configured from inventory that were manufactured in 2011 or later.  It's a good bet these machine don't show the full range of problems.  Worse case: they use virtual machines to test legacy configurations which will hide most hardware issues.

It will be very interesting to see how Apple responds. Conformance testing against legacy hardware is a touchy issue since Apple gets no direct revenue - only goodwill.

Mavericks works and Yosemite does not. As such, it is clear that Apple can write software to work with the affected ATI graphics cards if they choose.  The question is: Will Apple choose to fix the problem?

You may be eligible for a refund for your replacement video card:

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support