Q: OSX Lion + 2011 iMac 27'' + Video = Freeze

Well thank you apple the new 10.8.4 looks like it fixed my problem with ati drivers

Thank you for working and fixing it

Really? That's great news if it sticks.The screenshot you gave showed the same checkerboard artefacts we've all been experiencing so fingers crossed it's a fix for everyone.

Thanks for letting us now. Have to admit I wasn't going to update because I figured it would just make the problem worse.

And if it is a fix, I'm NEVER updating again:-)

wow! this is great news I will be updating tomorrow. the real test will be time. did you do the bios flash and I wonder how this reacts with and without it. I will deff update and write back.

I'm sure this is not what we are all wanting to see right now. For me 10.8.2 is still much more stable than 10.8.3 & 10.8.4. However please continue to post results and i'm curious to what kind of response you all have been getting from apple.

Sadly I can confirm Anthony's findings: 10.8.4 solves nothing for me and, like 10.8.3, actually makes the problem worse. No crashes yet but I've only just installed it and I'm getting the same artefacts Anthony is getting above.

This is really getting silly. If this is not a problem with the OS and is in fact a hardware problem that only affects a small number of machines (ie mid 2010 iMacs with ATI 5750 GPUs), I wish someone at Apple would simply confirm that as fact (although the company is unlikely to do so as it put the dodgy cards in the iMacs in the first place).

The bug reporting process is clumsy and largely ineffective. I've raised this with Apple engineers several times over the last few years and it hasn't made one bit of difference. My gut feeling is they've simply written this off as irrelevant - our 2010 machiens are just too 'old' to care about.

I'm telling you guys... the only way is to never let the screen go to sleep. It's been 5 months since I had my GPU changed... and no artifacts yet.

I'm glad that's worked for you, Johann, but for me it's not a practical solution. Is it really asking so much for a machine to work as it's supposed to?
Anyway, I just had a major crash with 10.8.4 - flashing windows and a psychedelic light show unlike anything I've ever seen before (which was fitting seeing as though I was listening to a Can album at the time) so I went straight back to a clean install of 10.8. If Apple didn't make it so difficult to do, I'd go back to 10.6 and be done with it. I'm even toying with the idea of switching full-time to Windows 7, which runs perfectly fine under Boot Camp.

The only thing to note here is the fact that 10.8.4 crashes immediately on my system (where 10.8 and 10.8.2 do not) suggests again that it's a problem with the OS and not the hardware.

Mine seems to be fixed....  I DID NOT do the bios flash.

I just wonder if they fixed it for the spec iMac not for ones that had their bios flashed.

I will report if I have more problems, but so far I am good.

And it was getting bad up to updating.

I would only get to work for about 5 mins before the artifacts started appearing and then locking up a really messed up screen.

Well I did have a few lockups after all.

I thought it was fixed because it was working all night then after around 8 hours i had a lockup.

And tonight tryoing to do suff more lockups!!!!

AND... while i was trying to write this it locked up.

Now what it is doing is shown on the youtube link below.

(if they allow youtube?)

http://www.youtube.com/watch?v=rAANQkhrGao

Well i am going to contact apple and see what they say.

PLEASE HELP APPLE AND DO SOMTHING

Really glad you shot that video because that's EXACTLY what happened on my machine an hour or so after I installed 10.8.4 (the "psychedelic light show") described above. See if there's a crash log in your Console - I reinstalled 10.8 as soon as I had that crash, which wiped out my Console logs.

Again, this suggests it's a problem with the way the OS interacts with the GPU. Good luck contacting Apple. But I strongly suspect they just don't test their OS releases on 'older' machines. I'd be very surprised if they have a mid-2010 iMac with the ATI 5750 lying around. I have offered several times to test possible fixes on my machine but never received a reply beyond 'our engineers are looking at it'.

I encourage you to report this "confetti effect" and psychedelic light show. After I reported the freezes a friendly Apple employee called me; I explained the situation and then have been sending them logs of different setups. In order to reproduce the freezes I had to restore the gpu bios to the original settings so it's fine that you haven't do so.  I feel like they are willing to help but I can only see two paths in the end:

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I give up!

My machine is an iMac 27 mid 2011 (out of warranty) 4GB Ram 3.4Ghz, 6970M 2GB

I was waiting for the latest upgrade before buying a new card. But the latest upgrade 10.8.4 did not fix this issue

system still freezes and screen goes blank.

I think it is the video card, sometimes after having opened the computer and cleaning the fans the computer works fine for a few hours but eventually issue resurfaces.

When I changed the resolution to 1280x1024 then I have no issues.

So what are my options?

I think it is the video card, sometimes after having opened the computer and cleaning the fans the computer works fine for a few hours but eventually issue resurfaces.

1- Should I buy a new Video Card? if so what is the cheapest one that would work with this machine?

       not ready to shell out $600 for the same video card nor do i need it high end.

2- Should I change the settings on the video card as per Andrew Humphreys post

       Anyone had some long term success with 6970M card?

3- Should I remove the video card and put thermal paste btween the heatsink and gpu?

       Anyone done this successfully

4. Should I sell it "as is" and get a newer one?

1 & 2 would be a pain as I would have to take the whole thing apart just to remove the video card

but willing to do it at least once.

Thanks for your input

When you go back to 10.8.1 do the problems leave?

I was just wondering what to downgrade to????

I no Longer have the 10.8.1, how would I go about getting it?

Yesterday, I re installed 10.8.4 from scratch. Interestingly, while the installation was going on the screen at full resolution did not have a single hitch. No artifacts or freezes. Then when the installation was over and the system rebooted the screen froze. So I am assuming installation must be using a more generic video driver like what windows does for installation. Is there a way to purposely switch to a more generic video driver in OSX?

ok it looks like I can replace my HD 6970M 2GB with HD 6770M 512MB for $209.

Can anyone please confirm or if you have a spare one (from an upgrade) that came from a similar system and interested in selling it let me know.

I am sick of having wasted so much time on this issue. I think we should all call Investor Relations and let them know how we are starting to loose faith in the Apple brand.