Just went through the exact same problem with my mid-2011 27" iMac with the same video card, AMD Radeon HD 6970M. But there were no glitches ahead of time, just a sudden blue screen with thin vertical black lines. A reboot brought up the gray screen forever. Rebooting from the recovery partition always got the blue screen. With another normal reboot it worked fine for two days and then wham, another blue screen. I took it to the Apple store and it took a little over a week for them to diagnose that it was the video card. It was my second trip in with this machine. The first was the notorius screen flicker on the left side many have had, under warrenty then. I expressed my concern that this machine had two strikes. No other Mac I've owned (since 1984!) has had so many serious problems, and that I was having a hard time feeling confident in this model. Long story short, they replaced it for free despite being out of warranty, wanting to restore my confidence in the Apple brand. That helps!
i had the same exact problem ! took off the graphic card put back some thermal paste just in case, i had no glitch or whatsoever on snow leopard or on bootcamp with windows.. but on Mountain Lion and LIon i had bad graphic beware + freeze ..
A bios flashing of the Ati 5750 with the same setting that Andrew Humphreys put just did the trick !
Everything is back to Normal !
Thx Buddy !
I'm glad to confirm that Andrew Humphrey's idea also solved my iMac freezes problem.
Mine is a mid 2010 27'' iMac that freezed up to 3 times per day at random intervals and other 3 times every time I started it. Since the moment I applied the changes a month ago I haven't had a single freeze. As previously, I have been doing basic stuff only, like browsing or watching videos. I don't know what could happen during intense graphics tasks.
I don't know if I did something wrong, because changing the GPU speed as Andrew said didn't worked but changing the voltage to .98 did. (It's in the same window where you modify the speed). This lead me to think that accumulated dust could be causing these variations in GPU operation, although I have not verified it yet.
The change is permanent. I have erased bootcamp partition, reinstalled OSX, reset the PRAM and everything continues ok.
I don't know if this voltage change can burn the GPU or consume a lot of energy, I'm not an expert. Do it at your own risk. In my case I couldn't lose anything because I tried everything for more than a year so this was one of my last options before giving up since I refuse to buy a new logic board that costs almost as a new iMac, as technical support pruposed.
The only issue that I have noticed is that if I watch videos for a long time, Temperature Monitor shows that secondary heatsink goes up to around 80º and smcFanControl shows that CPU fan goes up to 2100 rpm to cold it. It returns to 65º levels but the fans never calm down. I mean, fans don't spin like an airplane but I guess it's like half speed. I hope that everything is ok. I can't say if that's normal because in the past it never stayed on for a long time without freezing.
Thanks a lot Andrew and good luck everyone.
Thanks for reporting your findings, Carlos! Good to know what worked for you. I might give it a try myself, seeing as though my luck with 10.8 seems to have run out and I'm suddenly crashing again (always when the GPU is switching modes).
I think 0.98 is well within 'normal' voltage levels, so it shouldn't affect the card long term. And as you say, when it's a choice of being stuck with a machine that continues to crash and trying something to fix it, what have you got to lose? I've given up waiting on Apple to address the problem.
Not sure which support thread to post in anymore. However, has anyone noticed the 10.8.4 build's focuses? Apparently the focus areas are wi-fi, graphics drivers and safari. Hopefully this helps with something! It's still in beta so I haven't tried it. If anyone has I would love to hear your results!
I have been experiencing the following issues on my MacPro / ML10.8.3 / XFX Radeon 5770 for the past few months seemingly at random:-
1> Mouse pointer breaks up into vertical lines somtimes followed by the whole screen breaking up, either way the system becomes unresponsive and hard reset is required.
2> Screen just sudenly breaks up showing vertial lines on a solid background often greyish color, occasionally after time it will flicker go back to normal but more often than not the system just hangs needing a hard reset.
Looking through my error logs I have :-
09/05/2013 20:49:31.000 kernel: ** GPU Debug Info End **
09/05/2013 20:49:31.000 kernel: GPU hang: Not Implemented
09/05/2013 20:49:31.000 kernel: Trying restart GPU ...
09/05/2013 20:49:32.265 com.apple.launchd: (com.apple.DumpGPURestart) Throttling respawn: Will start in 9 seconds
09/05/2013 20:49:32.000 kernel: GPU Hang State = 0x00000000
Plus various other GPU related stuff. It seems pretty obvious that it is a GPU issue. Although I doubt that it is a hardware problem as I have used the very same card on a Linux box and have had no problems at all. To me it seems more likely that Apples ATI drivers are not handling these cards properly.
However I have just modded and flashed my cards bios and upped the clock speeds as follows :-
Original GPU 157Mhz
Original RAM 300Mhz
Original Voltage 0.95V
New GPU 400Mhz
New Ram 900Mhz
New Voltage 0.95V (Untouched)
Only time will tell if this has solved the problem but I'm keeping my fingers crossed
Hey all, not that anyone should care but i recently bought a new machine. The new 2012 imac with the nvidia card. I couldn't deal with the artifacts problem anymore while using my computer for work so I decided to upgrade. However I am still trying to figure out the problem and have compiled a list of personal notes that may or may not be helpful to anyone with our problem. I will still be testing/trying to figure this problem out as I am certain that it is not hardware related and must be driver problems. Right now i'm waiting for 10.8.4 to be released to see if this does anything. I do recommend that anyone with this problem write to apple and mention this support thread and include as much information as possible. For a company that is built around hardware and software being locked together we shouldn't be experiencing this at all. They made the choice to include the ATI cards in their iMac product line and should fix/offer support to this problem. Anyway, here is my unorganized compilation of notes.
Graphics Artifacting in OSX w. ATI graphics cards.
Known Systems affected.
-2010 iMac w. ATI Radeon HD 5750
-2011 iMac w. AMD Radeon HD 6970M
Other systems have been reported to experience the GPU artifacting as well. These two cards are the most known and commonly affected.
Different builds of the OS produce different results. This leads me and many others to know that this is a software problem.
Graphics artifacts are NEVER present in recovery mode and new OS installation mode?
Graphics artifacts show up on PRINT SCREENS and external displays.
Johann P recomends NEVER putting the display to sleep as this replicates the artifacts pretty quickly.
I have personally experienced the problem in later builds of 10.6 through 10.7 to 10.8 as well as many others.
Andrew Humphreys had come up with the first originally temporary solution. This involved flashing the GPU BIOS settings. The original power play settings were 157/300. In his fix the settings are changed to 400/900. Some have had limited success increasing their idle voltage from 0.95v to 0.96, 0.97 or 0.98. Personally I increased my voltage to 0.98. All of the information on this fix is originally documented at this link. https://discussions.apple.com/message/18398448#18398448 (It should be noted that this fix is only a temporary solution. That may last weeks or months.)
The two main Apple support threads documenting these problems are:
Apple has been made aware of this problem on separate accounts. I have personally contacted apple by sending an email directly to Tim Cook. I had then been contacted by an Apple executive representative and support technician who were working with apple engineers. At first they seemed very interested in my specific problem. They had even originally agreed with me that this must be software related. After a few days with no new answer Apple’s “Engineers” concluded that it was hardware related. They had wanted me to take my machine to an apple store to replace my GPU. I disagreed with them and did not take my machine in. The reason for not taking in my machine was because it was my main computer needed for work and I could not be without it for the estimated 4 days of service time. I also was reluctant to bring my machine in for a graphics card replacement because many users in the support thread have done the same to no avail. Many users experiencing this problem before me have had their GPU, PSU, Logic board, and Display replaced and have noted that the artifacting/graphics problems still existed.
All in all the problem is either error in design or driver related. These ATI cards are not agreeing with OSX after extended amounts of time and someone does not want to admit this.
I would like to compile as much information on this subject to help the users experiencing these problems as well as lead people away from buying any machines with the problematic ATI cards.
My Personal notes on 27” iMac w/ ATI Radeon 5750HD running in OSX.
Andrew Humphrey’s Original Fix (This fix only lasted a few months.)
GPU flash of power play settings from 157/300 to 400/900.
Also voltage increases from 0.95v to 0.98v
Print screens show artifacts as well as external displays
10.6 (This is where I originally experienced the artifacting. at this point in time I did not take notes on the builds that were affected.)
10.7 (Artifacting was similar to 10.6 if not better or worse. I did not take careful notes.)
10.8.0 (untested, however Andrew has reported originally that this build was stable but over time went bad.)
10.8.2 (This build was stable for quite some time until an unknown problem occurred which lead to artifacting.)
-Disabling the dock magnification feature improves stability and lessens artifacting. Does not completely fix the problem. (This can probably be explained due to the immediate change in the GPU clock cycle.)
-Resolution change. Less artifacts at 1920 x 1080.
10.8.3 (completely unstable/unusable (AppleGraphicsPowerManagement.kext was introduced which undoes the original BIOS FLASH fix)
10.8.4 (I am hoping that this build will have a fix as I have heard that it is focusing on graphics)
I believe that a graphics firmware update is what we need because even if 10.8.4 work there are people that prefer to stay in 10.6 or 10.7. You inspired me and I wrote Tim Cook, the severity of the issue deserve it.
It is important to notice that the fact that the mid 2010 iMac graphics card is not a Radeon 5750 as advertised but a Mobility Radeon 5850 could be causing this problem because developers could be making patches for a card that is not the indicated.
I'm also reading from you and TheAppleCore that your default voltage was .95V. In my case it was .9V
0: 628Mhz, 1000 RAM, 1V
1: 157Mhz, 295 RAM, .9V <-- First I tried changing to 398Mhz and 1000 RAM as Andrew Humphreys did but it didn't work. Maybe I did something wrong or that only applies if you have .95V, or other OS than Snow Leopard.
2: 503Mhz, 1000 RAM, .9V
3: 398Mhz, 1000 RAM, .9V
0: 628Mhz, 1000 RAM, .98V
1: 157Mhz, 295 RAM, .98V <-- All voltages except this one changed automatically as far as I remember.
2: 503Mhz, 1000 RAM, .98V
3: 398Mhz, 1000 RAM, .98V
It could be that more voltage compensates less Mhz.
The newer the OS, the more graphic hungry it gets. I'm running Snow Leopard at 1920x1080 and still without a single freeze so far thank you. Flashing the card really works but I'm not completely satisfied because software updates may reset everything and because I'm scared that heat could burn it someday or the problem might reappear suddenly with any minor graphic change that I haven't tested.
Well hello everyone, now I too am having problems.
I have a 27 inch iMac (Mid 2010)
Processor 2.93 GHz Intel Core i7
Memory 12 GB 1333 MHz DDR3
Graphics ATI Radeon HD 5750 1024 MB
Software OS X 10.8.3 (12D78)
I am going to try to do the bios flash thing, but this is very frustrating.
Just like the rest of you, I am having artifacts come up and about 3 or four mins, lock up with nothing but the cursor moving around. (clock froze and nothting is clickable.)
Usually i start up Lightroom and after about 5 mins the madness starts.
I mean with this much attention I hope that they are working on a fix.
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THIS WAS LIKE A 2400 DOLLAR COMPUTER!!!!!!!!
Please apple fix this or make it right.
If this is not fixed by the next update I am going to try taking it in and emailing Tim ect....
I am going to try to attach a pic showing my problem and how it starts before it locks up