Previous 1 2 3 Next 32 Replies Latest reply: Jul 18, 2015 11:22 PM by Ronald Prochat
Becjr Level 1 Level 1

My 24" iMac has been exibiting strange behavior lately...  It appears to be if a graphical nature where the screen will randomly flicker or go blank in a variety of colors (black or white or yellow or red or blue).  Sometimes a preceeding indicator that this is going to occur is that the system becomes on responsive or extremely delayed, text and other graphics appear garbled/corrupted/scrambled.


I've used Mac Hardware Test, Disk Utility, TechTool Pro 6, anti virus software - even took it to a local authorized Mac repair shop (not Apple Store) and the results are the same - Everything LOOKS fine with no problems reported.  I've reinstalled the OS and even gone as far as completely wiping the drive and starting from scratch, just incase it is/was some kind of odd software conflict.  Yet, the problem persists and the Console always captures something like this just before another epic fail:



4/13/12 5:55:50.000 PM kernel: NVDA(OpenGL): Channel exception! exception type = 0x8 = Fifo: Watchdog Timeout Error

4/13/12 5:55:51.000 PM kernel: IOVendorGLContext::ReportGPURestart

4/13/12 5:55:51.000 PM kernel: 0000006e

4/13/12 5:55:51.000 PM kernel: 00000010 0000502d 00000472 00000000

4/13/12 5:55:51.000 PM kernel: 0000047a 0000022c 00000001 0000000f

4/13/12 5:55:51.000 PM kernel: 00000000 00000000 01fffe03

4/13/12 5:55:51.000 PM kernel: 00000000 00000000

4/13/12 5:55:51.830 PM sandboxd: ([1021]) DumpGPURestart(1021) deny file-write-create /Library/Application Support/SubmitDiagInfo

4/13/12 5:55:51.851 PM sandboxd: ([1021]) DumpGPURestart(1021) deny ipc-posix-shm apple.shm.notification_center

4/13/12 5:55:51.853 PM sandboxd: ([1021]) DumpGPURestart(1021) deny ipc-posix-shm apple.shm.notification_center

4/13/12 5:55:51.854 PM sandboxd: ([1021]) DumpGPURestart(1021) deny ipc-posix-shm apple.shm.notification_center

4/13/12 5:55:51.855 PM sandboxd: ([1021]) DumpGPURestart(1021) deny ipc-posix-shm apple.shm.notification_center

4/13/12 5:55:51.856 PM sandboxd: ([1021]) DumpGPURestart(1021) deny ipc-posix-shm apple.shm.notification_center

4/13/12 5:55:57.000 PM kernel: NVDA(OpenGL): Channel timeout!



At this point, all I can do is force a system reboot.  To me, it looks like the NVIDIA card is having problems...  If so, then why does it check out as "ok" when tested (by myself & local Mac Tech)?


It'd be great if there was a program like this one here [NVIDIA 8600M GT] to help me with my current delima with the NVIDIA 8800 GS in my 24", early 2008 iMac.


With my machine being as old as it is, I'm questioning wheter it'd be better to have it repaired (if it needs it) or invest in a newer model.

iMac, Mac OS X (10.7.3)
  • Frank Caggiano Level 7 Level 7

    How did you re-install your OS, from the App Store? If so you might want to try downloading and installing the OS X Lion Update 10.7.3 (Client Combo)


    There have been instances were reinstalling from the combo update has resolved problems that a plain App Store re-install didn't.

  • Becjr Level 1 Level 1

    I started my iMac up in the Recovery Disk mode so I could use Disk Utilities to wipe my drive. Then I used the install OS X [Lion] option to install the operating system.


    I thought that fixed the issue because the screen saver [Flurry - at default settings] was performing much better after the wipe & re-install.  Then, while doing some basic tests, the problem sprung up again while trying to drag & drop a wallpaper from a web page in Safari to the desktop. This time there was much screen flicker and strobe-like pulses in horizontal bands across the bottom half of the iMac's screen before the whole screen went to a mustardy shade of yellow. Followed by a manual forced shutdown, of course.

  • Frank Caggiano Level 7 Level 7

    If you're system stays up long enough I would still give the combo update a shot. At this point you have nothing to loose.

  • Becjr Level 1 Level 1

    Absolutely right about that... Nothing to lose here.


    As soon as I get a chance, I'll give that suggestion a go.



  • Becjr Level 1 Level 1

    Well, it was worth a shot.  No joy, though.  The screen glitching still occurs and after looking at the Console log, judging be the number of this repeating issue in the report:



    4/15/12 9:44:21.000 AM kernel: NVDA(OpenGL): Channel exception! exception type = 0xd = GR: SW Notify Error

    4/15/12 9:44:21.000 AM kernel: 0000006e

    4/15/12 9:44:21.000 AM kernel: 00200000 00008297 00000474 00000010

    4/15/12 9:44:21.000 AM kernel: 0000047e 00001458 00000006 0000000b

    4/15/12 9:44:21.000 AM kernel: 00000000 00000000 00000603

    4/15/12 9:44:21.000 AM kernel: 00000010 00000000



    I'd guess it sends that error from the "kernel" for everytime the screen glitches/flashes.


    If I understand this right...   The video card's OpenGL is throwing some kind of exception - which I understand to be really bad, right?

    "0xd = GR:SW" - I have no clue what this means.

    All of the number groups, like "0000047e 00001458 00000006 0000000b", represent [video] memory locations, right?


    This is a pain because the hardware still checks out as "ok" and the only software I've installed and run to "torture test" the issue is Starcraft II (which I've played [at lowest graphic settings] since its release, what two years ago, without incedent).  Although I've had the problem occur using Safari, Pages, Launchpad,  and just moving things around in the Finder, so I don't believe the problem is confined to one specific application.


    Hmmmm....  [still thinking]

  • Frank Caggiano Level 7 Level 7

    Do you still have you're Snow Leopard disks? Something else to try would be to install SL and see if the issue changes. After that I'm reallly out of ideas.


    Back in my hardware fixing days we use to joke that if only the diagnostics could run the users software nothing would ever crash.


    I'll see if i can get someone with a more knowledge of the graphic end of thigs to have a look at this thread.



  • Becjr Level 1 Level 1

    Sure. I suppose I could try the Snow Leopard OS. I was an early adopter of Lion and hadn't had any problems up until about a month ago. The last thing I remember updating was my copy of SkethUp Pro; however considering I've wiped my drive and started from scratch I'm still stumped on this most bizaar problem I've ever had with any of my Macs.


    Of course, having said that, considering I've exhausted my reportorial of troubleshooting techniques (Mac user since the early-mid 90's [ xD ] the only thing I can think of that I'd love to have access to a spare NVIDIA card to swap out and see if that works (I understand that's possible w/the 24" iMac that I have). I'm just not convinced I'm ready to drop $350-$550 on the off chance that I may not entirely be a graphics card issue. At one point I cruelly considered it may have something to do with the audio because when I kept the system muted, everything seemed to work ok... But then not really (hahaha!)


    Thank you for all of you help and feedback so far though!


  • R C-R Level 6 Level 6

    I also have a 2008 iMac with the NVIDIA GeForce 8800 GS graphics system but I haven't had any problems with mine.


    I think the suggestion to try installing Snow Leopard is a good one, especially if you don't add any other software while you are testing with it. If the video issues don't go away, it almost certainly is a hardware problem, even if AHT can't find it.


    It's possible (but unlikely) the problem isn't in the 8800 itself. One thing I would check is the RAM modules, especially if you have upgraded them. If you did & still have the old modules, you could try using them to see if there is any difference.


    If not, it is probably time to consider a repair or a replacement.

  • Becjr Level 1 Level 1

    The Snow Leopard idea didn't pan out for me either.


    The RAM is the same 4 GBs that I opted for when I purchased the machine back in 2008. Techtools Pro 6 says that the RAM is doin' great. In fact it says the video memory "passed" its test. Too bad it's not more forthcoming with the details of that test, but maybe there's not a whole lot to report on. The only issues that TtP6 reported on was the SMART status of my hard drive - some search errors, temperature variance [test] failure, and some large file fragmentation ( which I found to be really odd considering I wiped the drive an started from scratch - I figured everything would be all neat & tidy w/ such a clean start - xD).


    At this point, I'm anxiously awaiting news of an upcoming iMac model refresh.

    ... I'll have to go check, but I wonder if the RAM in my current iMac would be compatible w/the newer models...  Knowing my fortunes...  Probably not.


    Thank you for the suggestions. You wouldn't happen to understand the code from the Console would you?  This whole experience is a waste if I can't learn something from this problem in case I encounter it again. I'm not use to running into a Mac problem that can't be identified in some way or another.

  • R C-R Level 6 Level 6

    I can tell you for sure that the DDR2 RAM can't be used with the newer models -- that's one of the things I keep track of.


    I don't know how to interpret the console logs all that well, just enough to know from prior experience that it isn't very reliable if there is a hardware issue involved. Unfortunately, the same is true for software based hardware tests -- because the software is running on the hardware it is testing, only some errors can be detected. It's kind of like a crazy person trying to figure out if they are crazy without any outside help, if that makes any sense.


    The one (kinda) bright spot in all this is what you said about TTP6 detecting a temperature related failure. That might mean the issue isn't with the graphics system itself & maybe could be fixed at a lower cost.

  • Becjr Level 1 Level 1

    I've been checking into as much information I could stand to regarding this error of mine and have been considering getting a new hard drive for my iMac.  I'm thinking it's possible that there could be something in the drive that's causing the malfunction - like putting your car in a parking garage and then forgetting which level/section you parked in.


    I've even read Apple documentation that points towards a kernal panic, which I have seen 2 time within the last 1.5 years (at least 6 months apart)...  But the general consensus on that seems to point to a RAM issue.


    Sadly it seems that I'm getting to the point of $100+ here and $100+ there...


    Oh, well.  I'll probably be getting a new drive within the next week or so.  If this seems to work, I will post an update for anyone else experiencing similar issues.

  • Jonathan_Horne Level 1 Level 1

    was there any resolution to this issue?  my 2008 Mac Pro is doing the same thing, and i have to force a reboot almost every day lately. 

  • Becjr Level 1 Level 1

    Unfortunately, no. I've all but stopped using my trusty iMac now. A few days ago I was deleting some files in the trash can and the screen just went black. Of course I had to force a shut down... Send the prompted report to Apple...  Then the screen turned a solid pinkish color...  And I almost put my fist through the screen.


    The most frustrating part about this all is that even after taking my iMac in for testing at my local authorized service shop, they couldn't find anything wrong with it!!  If I only knew what was the source of the problem, I'd at least have the solace of knowing what needed to be replaced. The only indicator that points to anything is the Consile readouts reporting an issue with the NVIDIA card just prior to the problem occurring. That sounds good and all, but it's not a certainty. I don't want to spend $350-$500 on a replacement video card only to have the problem persist [because of a motherboard, RAM, etc issue(s)]. I guess I'm waiting for that supposed iMac refresh later this year.


    It's a real shame that for all of the reports that I've sent to Apple following this problem with my iMac that some tech genius there hasn't responded with some helpful insight into the problem - I find it really, really strange that I've run the gamut of testing an troubleshooting possibilities just short of removing each possible piece of hardware potentially involved in this epic fail and having them individually tested somehow. ...Even though all the tests give no indication of any problems, and yet, clearly, my iMac is broken. I really expected this machine to keep running a bit longer than the 4+ years I've had it, after all, the "Bondi" I bought many [many] moons ago still functions just fine!



  • josefrombrande Level 1 Level 1

    I'm having a similar issue except I can only boot into safe mode.

    I never expected my iMac G4 to outlive a 4 yr old intel Mac but thats life.

    I've read quite a few forums describing issues with this nvidia 8800gs ( I've already replaced mine once), I hope apple and Nvidia do the right thing on this and replace these faulty cards, but I'm not going to hold my breath.

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