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  • paulmcg123 Level 1 (0 points)

    Glad your memory change fixed the issue for you, but I'm afraid that is not the universal solution.


    I'm having the same GPU white screen error on my late 2009 27" iMac core i5 10.7.5(11G63) with ATI Radeon HD 4850, e.g.


    7/25/11 9:40:42.000 PM kernel: ** Device in slot: SLOT--1 **

    7/25/11 9:40:42.000 PM kernel: ** GPU Debug Info Start **

    7/25/11 9:40:42.000 PM kernel: 0x00006720

    7/25/11 9:40:42.000 PM kernel: 0x0000008f

    7/25/11 9:40:42.000 PM kernel: 0x00000001

    7/25/11 9:40:42.000 PM kernel: 0x00000018

    7/25/11 9:40:42.000 PM kernel: 0x0000a880

    7/25/11 9:40:42.000 PM kernel: 0x00000001


    Comes up to a white screen with just a cursor unless I boot in Safe Mode.


    This only started when I updated to 10.7.5, never ever had any graphics issues prior to this. I have read read countless threads here and on other Mac forums, there does not appear to be any fix for this. The nearest I have seen is where people under apple care have had their entire logic board replaced.


    I can only suppose that the software update did something to the graphics driver, and Apple are not owning up to it as yet. Until then, I'm stuck in Safe Mode, can't run Parallels, Networking, etc. At least I have ethernet, so this is not just an expensive 4 year old heap of junk.


    The wierd thing is, my wife's 24" Mid 2007 iMac Core 2 Duo, also running 10.7.5 (11G63) but with ATI Radeon HD 2600 is having no issues whatsoever!

  • Lucas Nap Level 1 (0 points)

    Same here..


    If you want Apple to do something about this you should make a bug report at:

    I did.


    Apple does listen to bugreports.

  • hwlin Level 1 (0 points)

    I have a late 2009 Core i7 27 inch iMac. I've had so many problems with this computer from day one. To date the logic board, power supply and the video card have been replaced, and I have installed new RAM. I've had this problem on Lion and I still have this problem on M Lion.


    For me, the way Apple has dealt with this issue has made me sick. My local applecare service provider replaced my video card and charged me some $600+, and absolutely nothing was fixed. I returned to the service provider which recommended that I call Apple for a replacement unit. After talking to Apple on the phone for a week and explaining my frustration, they ended by saying there was nothing they could do and I should consider paying for the service provider to replace the monitor which would cost ~$500. Unwilling to waste more time and money on this expensive piece of junk, I declined.


    Like many people have already expressed, this issue is extremely costly (I run scientific simulations on my Mac and freezes can cost a week's worth of computation to go down the drain). I am deeply disappointed with Apple, a company which supposedly values customer satisfaction.

  • Gerard H Level 1 (0 points)

    Your complaint will fall on deaf ears. I have complained that my September 2008 IMac is having similar problems  I had to replace the hard drive in 2010 and in June 2012 I started having issues with the screen going black. I tried some of the quick fixes suggested on here which worked for a while until the screen finally went black for good in July. After numerous letters and calls back and forth with Apple I as told in the end that my complaint was different from those on here because it was my LED screen that as bad. It would cost $530 to repair and they would not reduce or waive the fee on such an "old" computer I have been buying PCs since the early 90s and not one of them  ever stopped working   They just became outdated or slow and handed down to friends etc. Now I buy the supposed top of the line in the computer world, APPLE and just short of 4 years it is useless.  Was very disappointed in Apple's attitude towards a loyal customer , IPADS, IPHONES, APPLE TV etc 


    <Edited By Host>

  • apps2012 Level 1 (5 points)


  • paulmcg123 Level 1 (0 points)

    Late 2009 27" iMac core i5 10.7.5(11G63) with ATI Radeon HD 4850


    System has been up for 5 days now while I completed my first backup after reinstalling 10.7.5 - yes, it took that long. I have not run any applications in that time, apart from software update.


    Unfortunately, this morning the screen was locked up, blocky graphis and spinning wheel. Checked the kernel.log from PuTTy and it was the GPU error again, however, according to the system log, the next backup had started, also still had samba access to my shares. When the backup completed I did a shutdown -h.


    Since my install DVD is not reading, I had copied my AHT from the DVD via the wife's iMac, so finally able to do a hardware test using the D startup key.


    Alert! Apple Hardware Test has detected an error.


    4SNS/1/40000000: TH00-9.000

  • joeygillis Level 1 (0 points)

    This is a freakin nightmare.


    Yesterday I upgraded to 10.7.5, hoping against hope that this upgrade would fix the problem.


    Not only did it not fix the problem, but it CREATED a new one:  Now after several minutes the screen just goes black and nothing makes it come back on.  This is a problem I had with Mountain Lion, and now the Apple geniuses seem to have figured out a way to make it happen in Lion too!!


    At what point does Apple start owing us money for basically destroying our machines??

  • conorfromvictoria Level 1 (95 points)

    This error is a temperature sensor error that occurs after replacing your harddrive. Many IMacs have this problem when replacing / swapping out HDs.


    Here is something to try:


    Download smcFanControl 


    This will monitor your fan and temperature at the core. Have this running after you do the PRAM reset.


    Next after installing the program.


    to a PRAM reset.


    1. Shut down your Mac.
    2. Locate the following keys on the keyboard: Command (⌘), Option, P, and R. You will need to hold these keys down simultaneously in step 4.
    3. Turn on the computer.
    4. Press and hold the Command-Option-P-R keys before the gray screen appears.
    5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
    6. Release the keys.



    This has found to help the above problem. If the problem persists, I'd call Apple as it's directly related to how Apple designed the iMacs.

    Also after doing the PRAM reset, run the Apple Hardware test again, see if you get the same error.

  • paulmcg123 Level 1 (0 points)

    Haven't had time to redo AHT, but I installed smcfanControl, however, with HD fan set to minimum the system locked up after about 5 minutes. I got it back up and set HD fan to the maximum value, running at around 4570 rpm, and its been up a few hours now, temp between 39 and 41C.


    Actually this is not a replacement hard drive, its the original Seagate ST31000524AS, so I shouldn't really need the smcFanControl. I'm wondering if the 10.7.5 update maybe wrote to the HD firmware somehow?


    Anyway, late breaking news just read this a few minutes ago, apparently Apple is now extending their iMac 1TB Seagate Hard Drive Replacement program to some late 2009 iMacs.


    I just checked my serial number, and I am covered, so I will go on from here.
    The iMac serial number you entered is eligible for this program. Please follow the instructions below to have your hard drive replaced.

  • Neill Brooks Level 1 (5 points)

    I have the same issue with my mid 2010 iMac 27", screen freezing, spinning beach ball of death, blank screen Kernel panics and bad screen redrawing.

    The iMac was fine with 10.6 through to 10.7.3 .... 10.7.4 through to 10.8.2 the machine was totally unusable.

    It's now with Apple for a new graphics card and a replacement Seagate HD via an out of warranty repair (£236.00) HD is a free exchange.

    I'm skeptical as the Apple Genius hardware tests found nothing wrong with the hardware.... I will find out for sure in 7-10 days.


    It has been the most unreliable computer that I have ever bought, whilst the Apple support have been very helpful.... Why on earth do I have to carry a 20kg  27" iMac for 3/4 mile from my car to the store.... Why can't I use a courier to transport it like every other large PC manufacture, I would pay !!!...... fed up with a sore back  !!!!!

  • Gandalf The Grey Level 2 (275 points)

    Gerard H:


    I have had a ton of PC's since the 90's as well and everytime I try to upgrade the OS the machine went all to ****! In fact I had at least 5 machines on the PC end that went completely downhill, at least Apple Tech Support isn't in India where they ask you if you have your machine plugged in. LOL My 2011 iMac got completely tosted after Lion it was fine with Snow Lepoard, So I guess Apple is no different in my book but to me they have a way better track record so far and I will give them another shot with a new iMac when they come out till they I will not touch one. Ironically I have 2 Macbook Pros and a Mac Mini all running Mountain Lion with very little issues, so not sure why these are affecting mostly iMacs. If I was to have an older machine, I would erase everything and put Lepoard back on it, if you can, as that is the most stable software Apple I think they have had to date. This whole software hardware issue reminds me of updating from Windows 98-Windows Me and Windows XP to Windows Vista etc . Ironically this thread is suppose to be about 2011 + iMacs and Lion so I am supprised to see much older machines posted on here. Regardless if the specs say you can run Snow Lepoard/Lion or Mountain Lion on a older machine you should be able to do so without all these major issues popping up! (Frustration!)  Frankly I wish I could go back to my 2010 iMac with Lepoard which was rock solid fast machine. What is the wierd thing with Lion on my Mini I was luckly if I could open 2-3 videos and play them back at the same time with ML, not an issue at all. Only reason I am using a Mini is because my 2011 iMac was deemed un-repairable.


    Paul: Thats the same B S I went through as it all started with them pointing the finger to my hard drive but mine was the 2 TB.


    Neill: I would go back to Lepoard or Snow Lepoard if you can, seems like when the upgrade to the software happens just after the latest install of Snow Lepoard to Lion was the downfall of my machine.

  • jjjjjjb Level 1 (5 points)

    Hey, it's not a Lion or Mountain Lion issue.  How do I know this? Because I've had the same problems big time: fixed twice with replacement graphics cards (problem solved - for now) and I'm still on Snow Leopard. 


    So these problems are not due to the OS version number.

  • Gandalf The Grey Level 2 (275 points)

    JB: First I need to learn how to spell "Leopard" LOL   But most of my issues starting happening with late versions updates of Snow Leopard that is documented on here. Frankly I am thinking of going back to a Mac Pro as I never had hardware of software issues with those machines, just wish they were as updated as the new iMac, example "Thunderbolt" ect...

  • Marjean54 Level 1 (0 points)

    I am working with Mountain Lion on a 21.5" Mid 2010 iMac.  After upgrading to Lion, I started having the unstable windows, freezing while the curser still moved so I would have to shut down constantly.  I corrected the problem by going to preferences>Mouse.  I unchecked everything under "Point & Click" and "More Gestures".  By having those items checked, everything was way too lose and freezing occurred.  I haven't had a problem since.  I upgraded to Mountain Lion and still no problems.  I know it seems quite simplistic, but...

  • paulmcg123 Level 1 (0 points)

    Late 2009 27" iMac, I may have found something that works, at least for me.


    First, I decided to re-install Lion, I was expecting to have 10.7.0, but even doing it with Lion Recovery, it gave me 10.7.5.


    I had to get my /System/Library/CoreServices/.diagnostics/ from backup, since my "Super Drive" is still stuffed, thats the only way I can do AHT, but still haven't run it yet.


    I have ssdfancontrol being run as root, HD fan seems to be about 4750 rpm, but at least its cool.


    I stopped using both Chrome and Safari, apparently there is an issue with the way they use Adobe Flash. Firefox is OK, it has its own "embedded" version, if that's the right term.


    So far, after 3 days, not seing any of the errors in kernel.log that usually preceded a crash/freeze. I'm back to running Windows 7 on a Parallels VM, and the laptop is packed away for now.


    As for the Seagate 1TB HD replacement program, looks like I may be just getting a credit for what I spent back in January 2012 for the ST31000524AS (could never find the Apple ST31000528ASQ drive anywhere). I wish they would just send me the Apple certified 1TB drive rather than the refund.