Mid 2011 iMac Graphics Problems with Yosemite

Done. But it didn't solve my problem of green/red flashes. I still get a few now and again. They just don't seem to lead to a whole system crash (freeze) as before.

I have the same problem with a 21" iMac.

AMD Radeon HD 6770M 512 MB

UPDATE: have been running fine with transparency OFF for quite some time now. But I do admit I encountered a slight distortion caused by the ominous colored boxes once. System didn't crash though and boxes were gone after switching to another window. Still hoping for an update in 10.10.1 that solves this definitely.

same here. Happened once, but at least it didnt crash.

I through Leap Motion (V2) out of the menu bar (little Hand) and the strange graphic blocks are gone.

I've had this problem for about 24 hours now, so I'm turning to these forums to share my situation.

I have an iMac, 27-inch, Late 2009, 2.8 GHz Intel Core i7, 8 GB 1067 MHz DDR3, ATI Radeon HD 4850 512 MB. It's been a wonderful machine, and used it daily for years. I've been updating OS X since Snow Leopard, all the way up to Yosemite, and I've never had a problem, not ever, not once, not until now.

I came home yesterday and resumed using my iMac, went to Safari and started watching a video on YouTube. Then all of a sudden, pink lines appeared vertically down the center of my display. I realised that this distortion had also frozen the screen like this. Curiously, I could still move my cursor over this frozen image, and, I could still hear my YouTube video. It's was as if the entire desktop and it's windows had frozen together as one corrupted looking image, but other aspects of OS X were still working.

Being unable to see what I'm doing on my computer, I forcefully shut down the computer and restarted it. Attempting to fix the problem, I rebooted into recovery mode, tried a disk repair, reset the PRAM and unplugged the power. Nothing seemed to work – the problem seems more complex.

My issue is reproduced by simply booting into the login screen, or even booting directly into the desktop (automatic login), which reproduces the issue pretty much immediately – as soon as I have booted into OS X (after the grey boot screen) – noticeable graphic artefacts, pink and green noise and pixelation appears, and the image is frozen. Visually, my machine appears unresponsive, but as I reboot, my Mac still joins the network, I constantly hear the hard drive I/O, and I can SSH into it. Not being able to use the screen, I tried reading my system logs from another device using SSH, though nothing out of the ordinary indicates what the problem could be.

Now, not knowing much about either service, I'm just going to insinuate here that something like SystemUIServer or WindowServer is having a panic attack, whether it's a bug related to Quartz or a kernel extension – I have no idea – but I'm convinced my issue is not related to hardware – I'm able to "Safe Boot" straight into my desktop (after some time) and use my computer quite competently, albeit in safe mode. It leads me to assume that my logic board hasn't fried, my GPU hasn't exploded, and my RAM hasn't been corrupted. It should be software based.

I've read in this thread that deleting caches, LaunchAgents, and other files which could affect startup is advisable, though from what I've tried it hasn't fixed problem. I've also read that people had unusual success with installing, updating or uninstalling Java, but the problem still persists for me.

What I'm more concerned about is how widespread this issue could be, having upgraded to all the versions of OS X since Snow Leopard and never having any issues, I have no idea what I could have done to have caused this issue on Yosemite. I had been using Yosemite for weeks, and I'm completely puzzled by how simply playing a YouTube video in Safari would cause what seems like an irreversible compromise of my system. I am speechless about this one.

With my issue recurring pretty much right after booting OS X, the only way I can use my machine at this point is with Safe Boot... unless there is something I haven't tried yet in this mode – not knowing where the source of the problem is, I think my only option is to clean install Yosemite and cross my fingers that it doesn't magically happen again.

I have no idea what caused it, no idea how to fix it, and the fact it seemed so spontaneous makes me feel like it can happen to anyone.

Transparency OFF did the trick for me.

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

Same issue here. I have a late 2009 iMac 27" i7 2.8GHz, never ever had a problem with this machine. It even worked without problems after the Yosemite update. Just out of the blue, while playing World of Warcraft the screen got black and the machine crashed, since them I have the same issues a lot of people described here.

Switching off the transperency did the job, so far. I as well tried to uninstall Adobe Flash and switched on transparency again. So far no problems.

For all who even can't change the transparency, because you can't see anything, just keep on rebooting. It always came back, somewhen, in a state I could work/see anything. The most, I think, I was rebooting the machine 5 times, then I could go to the preferences, just found there a black panel, but after clicking a little bit around I luckily hit the right one.

I really hope there will be soon an update for this!!!!!!

Minimizing transparency also did the trick for me. Well, almost. A few pixel blocks showed up once a few days ago but disappeared after that part of the screen was refreshed.

For now disable transparency and uninstall Flash alleviated the problem. But I'm still suffering with some locked and forced reboots the system.

I have posted: I took my mid-2011 iMac 27" with the AMD Radeon HD 6770M 512 MB into my closest repair shop, and although it took a while, they finally got the message, and replaced, REPLACED the card. They are failing all over the place, and creating with is a software/card discrepancy, and creating issues from blinking pixels to pink and or black lines and freezes.

I can appreciate the fixes that I've seen on this and other threads, but I tried almost everything I read about, and found the fixes to be temporary, or 'sort of OK' which (HEY APPLE) not good enough.

Go through top level tech support, tell him you want the card replaced (they are warranted for FOUR years) and hope he/she is smart and cooperative.

The best!

I think its 1-800-my-apple.

Same here. I also took my iMac to the Apple store and supposed to get a replacement for free. While they are currently out of stock and I need to wait 1 week around.

Best.

I had the same problem. I was able to fix the problem by deleting Chrome web browser (and all traces of Chrome under HD/Library/Chrome and Library/Google/Chrome). Then I repaired permissions. After about 3 days of no video problems, I re-installed Chrome. It has been 5-6 days and I have not had any problems since.

At first I did the same tail-chasing-wipe, reinstall, disable this and that, re-reinstall, restore, re-install, mess with several settings, but in the end, it kept on coming back. In an hour, in two days, etc, etc. I wanted to get my iMac stabilized as much as everyone, but in the end, like dli23, and others, since finding out that the Radeon 5770 was warrantied for FOUR years (surpassing the applecare time) I took it in and had it replaced. NOW, its fast again, no pixelation, no artifacts, no problem!

Yeah, I ended up doing the same thing.

I was so certain the issue was software based, trying clean installs and messing around with kernal extensions. Eventually after 2 days, the visual artefacting started happening right from the EFI boot, where I figured it wasn't simply software based anymore.

I've taken it to a certified repair shop to have it looked at, most likely expecting the video card to be replaced. The technition told me that replacing the card requires an exchange; they send my old card to Apple, Apple send them a new card, plug it in, boot it up, and fingers crossed.

At the end of the day I'm a little suspicious to hear that the new R295X clockspeeds are being throttled, while hundreds of other discrete GPU's seem to have started dying on Yosemite. I mean, my iMac was 5 years old, but people with much newer systems are getting the same problems, some more severe than others. Something is definitely fishy about Yosemite.