Currently Being ModeratedNov 2, 2013 4:09 AM (in response to Ashadur)
Hi, I hope you find this information useful:
A few years ago, we purchased iMac 27" 11,3 (Mid-2010) (with i7 2.93Ghz, ATI 5750 1GB VidRam, etc.) for our offices and software development team. They were originally shipped with Snow Leopard and worked as expected and without any problems. However, a year later, we upgraded to Lion and all of machines immediately exhibited the same problem: the screen would go to sleep by itself and would require a hard reboot or sleep on/off. (Only the screen was asleep and the rest of the iMac continued to function; this was confirmed by screen sharing to the machine.)
Due to the severity and impact on our business, we immediately contacted Apple and their genius bar staff in New York/SoHo. They were unable to determine the root cause, so they replaced all of the logic boards, video cards, and screens, and got us back online asap. This resolved the problem, but we were curious to know why. After days of rigorous testing, we concluded that the issue is caused by a bug in MacOS. Specifically, faulty Kext files (Kernel Extension files extend the functionality of the MacOS Kernel) for the ATI drivers. So, why did the replacing the hardware work? We think that the Kext files that were released and distributed with Lion (and later MacOS versions) correctly supported the newer hardware revision of the replacement components, but not the older ones.
If you're experiencing this problem, short of replacing the components or waiting (for another 3+ years) for Apple to hopefully fix their OS software, you can lessen the effects and be able to recover faster by doing the following: (Please bear in mind that these are not permanent fixes.)
- Turn on "Hot Corners" and assign one corner to "Put Display To Sleep". When your screen goes to sleep, move your mouse (which still works) to that assigned screen corner for a second, then move it again. This will wake your screen. You may have to do this a couple of times, but it's much faster than a hard reboot or a sleep on/off for your iMac.
- Turn the brightness of your screen to a low setting (10%-15% of the total brightness).
- Turn on screen sharing, so you have a last resort method of accessing the machine.
If you're not convinced that it's a MacOS software problem, then do what we did and see for yourself; install Windows 7, Windows 8, or Linux via Bootcamp or as the only OS on the iMac. Those operating systems and drivers worked flawlessly for us; the bug does not occur and the screen does not go to sleep, but if you dual boot and switch back to MacOS, the bug reappears because the iMac is loading faulty Apple MacOS software.
Currently Being ModeratedNov 2, 2013 6:07 AM (in response to MarkusWinter)
I totally agree with your conclusion that "something", like video divers, in Lion and onward... is causing this issue in that vintage of iMac.
So... has you upgrade to Mac OS 10.9 "Mavericks" slowed or eliminated the video blackout issue? The post by "Only XM" gives hope! I have my effected machine in the hands of a friend. It has been "retro'ed" back to Snow Leopard, the original OS for this machine, and is running just fine on 10.6.8. When you can, please report your findings.
Ponca City, OK
Currently Being ModeratedNov 8, 2013 7:35 AM (in response to philfromhorw)
ok, my screen has now gone black it wont come back on, looked on utube, there is a vid on there how to fix this problem, tried it, didn't work, so i found a workaround, thunderbolt connector to DVI, i think its called (thunderbolt to another monitor) bought this cable, £20 from PC World, apple store 1 hr drive, PC world 15 mins, found a spare monitor, plugged all in, nothing worked, both screens black , but then pressed COMMAND F1 BOOOOOOOM ............... only joking spare monitor is mirroring the iMac screen, so all working again till i can get a replacement screen.
Currently Being ModeratedNov 9, 2013 7:40 PM (in response to Ashadur)
Hi. I purchased a used iMac 27" 2011 over the summer at a good price. Great computer, busted screen -- frequent, sudden blackouts, as described. Seller claimed no knowledge of this problem. Hot corner work-arounds were okay, but still frustrating. I saw on other thread about replacing the LED board, so thought I'd try this before selling the machine again.
It worked! No blackouts since the installation of the new LED board. I bought a new, sealed LED board on eBay for $35 and swapped it out within 15 minutes using iFixit instructions. I'm sure an Apple Genius can do the same thing for $250 parts & labor, but I'm psyched about my easy (and cheap) fix.
So sorry about the others experiencing this problem. I can't guarantee it will work for everyone, but it seems reasonable to replace this simple part before throwing your machine out the window.
Currently Being ModeratedNov 10, 2013 2:42 PM (in response to reilsen)
Encouraging news. Would you mind sharing more technical information about your fix? I.e. part number(s) of the replacement, ebay seller you purchased it from, etc.
Currently Being ModeratedNov 10, 2013 5:22 PM (in response to floremin)
Hi. The LED board "kit" is part number 923-0047. It contains two different (but visually similar) LED boards that are coded to the different display panels used in the 2011 iMacs. You have to remove the panel to see which part it is, which is why they sell the combo-kit -- it would be nice to buy only the one you need, but that requires opening the machine twice. I now have an extra LED board for the "other" display panel, in addition to the defective one. The eBay seller I found seems to sell an occasional part, but is not a distributor.
Currently Being ModeratedNov 14, 2013 2:26 PM (in response to Ashadur)
I have the same problem with a 27" iMac, purchased in November 2011 (UK) The screen will suddenly go black, although the computer is still running in the background. I discovered than if I pressed the On/Off button once & moved the mouse around, the screen would come back after 30 seconds or so. I've sort of stopped it happening by reducing the brightness, but it's obviously not ideal & I'm worried that one day, it will black out completely & then I'll be stuffed! When the Mac is off or asleep, there is a white feathering at the 4 corners of the screen
It seems that Apple has identified a problem with one graphics card (AMD Radeon 6970) and they will replace it free of charge. However, my graphics card is a AMD Radeon HD6770M, which is supposedly OK. I contacted techinal support via the Apple website, gave my phone number - and they called me immediately. My Mac is coming up to 2 years old, and thus out of guarantee & I don't have Apple Care. I thought I was going to get landed with a huge bill to replave the graphics card & screen. But to my surprise, as I live in Europe, I was told that under EU Law, the warranty is effectively extended to 6 years from date of purchase if there has been a hardware failure. Problems caused by accidents, spillages, mistreatments etc will not be covered, nor will problems caused by third party software.
I've booked an appointment with my local Apple store tomorrow - so we'll see how I get on. I'll post again hoping that what I was told actually happens.
Hope this helps those of you with the same problem living in the EU. I don't think it applies in the States/Canada though.
Currently Being ModeratedNov 15, 2013 10:13 AM (in response to Only XM)
Did not use my 27 mid 2011 Imac for almost half a year as the screen kept randomly switching off. Just out of curiosity installed Mavericks turned down the brightness and to my amazing screen is already stable for one week…
Currently Being ModeratedNov 16, 2013 5:32 AM (in response to drunknmonk)
Took my 27"iMac in to West Quay store in Southampton yesterday & I was pretty impressed. They examined it and ran a series of tests - which supposedly said there was nothing wrong. They have kept the computer to see if they can replicate the problem (ie screen blacking out). They have suggested that it's the dispaly panel and will replace it - free of charge - under a Consumer Law claim. Please note that this only applies to products purchased in the EU. In England, this effectively extends the warranty to six years (5 years in Scotland for some unknown reason!)
With regard to the white feathering marks at the edge of the screen, they suggested that this could be caused by smoke damage.
The only downside is that the repair could take up to 2 weeks! which means that I'm writing this on a clunky old PC running XP.
Currently Being ModeratedNov 30, 2013 6:38 AM (in response to jackofspeed)
It would be nice if the US had the same Consumer Protection Laws.
I have been dealing with an iMac lemon for years.
It took me countless hours of documentation, several weeks of leaving my computer in AppleCare's posession, and timesnoops/datacaptures/etc. to finally reach a resolution on the screen.
They finally replaced the screen and LED backboard and it seems to prevent the blackouts now. I still have the WiFi and Bluetooth issues, which they already have timesnoops and datacaptures on..
I asked them to replace those modules when they did the screen, but they didn't, and now want me to do timesnoops and datacaptures AGAIN... stating that if the machine has parts replaced, I have to redocument issues.
How does replacing the screen and LED backlight even possibly fix bluetooth and wifi? It doesn't. It's just a delay tactic.
At this point no choice but to contact the BBB in hopes for a resolution. I don't think it's my job to continue to troubleshoot this lemon.
Currently Being ModeratedNov 30, 2013 6:48 AM (in response to jackofspeed)
Sorry Goomband - the only thing I can suggest is that you cross the pond to live!
I've now got my iMac back - and .... so far, so good. Apple replaced the LCD panel - at a cost of £434 - which as explained earlier, I didn't have to pay. The new part has a 90 day warranty on it, but in any event I'm still covered under the European Consumer Laws.
Apple apparently ran a series of "exhaustive diagnostic tests" and also left the Mac running for about 9 hours with several videos running and at full brightness.
Generally, I'm very happy with the service I've received from Apple. The only downside was being without it for nearly 2 weeks!
Currently Being ModeratedDec 2, 2013 10:12 AM (in response to drunknmonk)
Did you get your iMac sorted? Worthwhile contacting your local Apple shop & talk to them about the EU Consumer Laws. (Apple do publish it on the website under guarrantees) Good luck!
Currently Being ModeratedJan 11, 2014 6:54 PM (in response to Ashadur)
For what it may be worth, here is my experience. I have a mid-2011 27" iMac. Under OS X 10.6.8, I never had any issues with the display. I didn't upgrade to Lion, but I did upgrade to Mountain Lion. For me, that's when the issues started. I started a thread about it here ( https://discussions.apple.com/message/22865181 ) but never gota resolution. Even after upgrading to Mavericks, the issue persisted. I noticed that if I didn't let my iMac go to sleep at all, that would help the issue somewhat.
Reading through this thread, I thought I would comment on my personal experience with some of the possible causes.
Temperature: For me, this was not an issue. My iMac is in a room that is anywhere between 70-80 degrees Fahrenheit and I've had the iMac display randomly turn off independent of the room temperature. That is, keeping the room cooler didn't keep the iMac display on.
Video card: This too seems to not be the issue for me. I have two external monitors connected to my iMac and when the iMac display goes blank, the two external monitors work just fine. There's no hiccup or anything, just the iMac display going dark. Additionally, I took my iMac in to the Apple Store (by the way, the 27" iMac is a pain in the butt to lug around!) for the 1TB hard drive replacement program and also for the AMD GPU replacement program. The hard drive was replaced, but the Apple techs said that the GPU was not eligible for replacement because it didn't fail when they ran the diagnostic. They said they would only replace the GPU if it failed under a specific test.
Backlight: This did not seem to be the issue for me. When my display went black, even if I shined a flashlight into the iMac display, there was nothing. I couldn't see a faint trace of anything, it was just black.
Software: So far, in my case, this seems to be the most likely culprit. I did a clean install of Mavericks after getting my iMac back, and it's only been half a day, but so far, my iMac has been able to go to sleep and wake up with no display issues. Previously, upon turning on my iMac, the iMac display was guaranteed to intermittently or permanently (for that boot cycle) go black within an hour.
Previous to doing a clean install, I tried all the normal things to fix the issue, including repairing disk permissions, resetting the SMC, unplugging external displays, etc...but none of those worked. So for those of you still experiencing this issue, as much as a pain it may be, a clean install might be worth a shot.
If the problem returns for me, I will report back.
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