Currently Being ModeratedJan 17, 2013 11:30 AM (in response to sf1234)
Thanks for the good datapoint sf1234. I was not aware of the fan control software. I'm using it now.
Now a question. When your main video blacks out, I believe I read from your post that the external display DOES NOT black out? Is that correct?
Ponca City, OK
Currently Being ModeratedJan 17, 2013 12:25 PM (in response to sf1234)
Also... DavidNY63 reports that he went back to Lion 10.7.5 and the video blackouts have not reoccurred. I am not able at this time to re-image, and really hate to give up a lot of the Mt. Lion features that I love, so will hope the internal fan regulation and using an external fan help me limp along.
Currently Being ModeratedJan 17, 2013 3:24 PM (in response to mebyard)
Mark- yes that is correct. Only main iMac screen blacks out, not external display. Btw, been using the fan control software all day today, with the brightness at 5 clicks above the minimum, and no black outs all day today (after 7 blackouts yesterday). Keeping my fingers crossed!
Currently Being ModeratedJan 18, 2013 6:08 AM (in response to sf1234)
OK, thanks sf1234. I'll be the first to admit that I'm no engineer, but this data point SEEMS to say that the problem is NOT with the video card. This SEEMS to say that the problem is actually a fault with the LCD backlighting circuitry! AND this theory is supported by the fact that those who have/had Applecare coverage, and had this problem occur, had their LCD backlighting panels replaced and that SOLVED their problem. I read about these on other discussion boards.
So... for those who are still able to work with Apple about the issue, this data point pretty much localizes the problem in the LCD backlight circuitry. There is obviously a heat-exacerbated issue with many of the panels that backlight this model of iMac 27".
So, where does that leave us that have no Applecare extended warranty, and have no money to have the LCD backlighting panel replaced? There is hope in the discovery posted by sf1234: the use of fan-control software! I have follwed sf1234's lead and installed smcFanControl, a piece of software from Eidac.de. Go to...
and download his smcFanControl 2.4. Install and try. When starting the application it runs on the menu bar. Here are my very encouraging findings...
I significantly raised fan speeds on all three choices (ODD, optical disc drive; HDD, Hard disk drive; and CPU) to get more flow out of the vent. You can hear the fans; it is a significant increase in fan noise but you can actually feel the air coming out of the vent! I also had a small room fan blowing across the top of the iMac from L to R to help remove heated air. With this situation, and a pretty cool room to start with, I was able to run the LCD back at NORMAL brightness most of the DAY and NO VIDEO BLACKOUTS! My normal operating brightness is 3 clicks below MAX! So this is encouraging!
Now, some might be annoyed with the fan noise. But, it seems for us without Applecare, it is either fan noise or no backlighting! I'll gladly take the fan noise and be thankful for it!
Thank you sf1234 for posting!
Now, as the ambient temps go up I expect to have to run the fans at higher and higher speeds. When summer comes back to Oklahoma (and that means triple-digit temps) and my house heats up significantly, we will see if internal fan control can keep up with the heat load. Until, then, I'm encouraged!
Regards to all... keep postiing!
Ponca City, OK
Currently Being ModeratedJan 22, 2013 7:54 AM (in response to mebyard)
I have a 27" iMac from 2011 and also have the same issue. It started in september last year without a real "Change". After a couple of hours the screen would go black with the power button I would put the iMac in sleep mode and by hitting a key wake the iMac again. Then I could work again for about an hour and had to repaet this procedure. Only the time intervals became shoter and shorter. When leaving the Mac over night in sleep mode I could work the next day but end the end of the day the problem started over again. By reading this discussion in september I found out the ctrl+shif+eject only switches the video off and hitting a key turns it back on. This improved my procedure but did not solve the problem.
I have tried all the options in this discussion (clearing PRAM, Save Mode, Clearing SMC) but without any succes. I even installed OS X again without solving the problem. Running at very low brigness levels did not work either it was a small improvement. When running at low brightness I noticed that before the screen turns black it starts to flicker. I found out the when I increase the brighness level until the flickering stops the screen does not turn black!!! On my iMac I found that when I increase the brightness level above 50% the problem disapears.
In discussion https://discussions.apple.com/message/19477888#19477888 they come to the conclusion that there is a bad connector between the LED back light cable and the LCD. I think this connector is influenced by temperature, when the iMac is warming up it starts to fail. This explains why the the problems only start after a couple of hours. Decreasing the brightness slows the process of warming up as does increased fan speeds. Ambiant temperature also plays a rol which explains the fact that the problem occures random and is difficult to repeat. Putting a stronger signal on the LED back light cable makes it less sensitive to a faulty connector. When Apple replaces the LCD at $$$ they also replace the cable and connector and it solve the problem.
I hope this helps.
Currently Being ModeratedJan 25, 2013 8:02 AM (in response to SuperJA)
Thank you for your "data point". It is appreciated. I suspect that you are correct about the LED backlight cable connection. I have also seen that post.
My particular experience is a bit different however, in that by increasing my screen brightness into the upper range will ALWAYS cause imminent video blackout. With the installation of the smcFanControl application software from eidac.com, I am able to live with the problem... at least now during our winter time in Oklahoma. If I can keep the smcFanControl temp readout to below 90F (using internal fans and an external fan if needed), I can usually avoid the video blackouts if I keep the brightness to mid-range or lower. Pushing the brightness above the mid-point will usually precipitate a blackout... eventually.
As our spring turns to summer, and my house warms up with the weather, I'm sure I will not be able to continue using the machine except perhaps in a darkened room and the screen brighness very low.
I appreciate everyone's contributions to this thread. The observations and suggestions have helped those of us who are "out of warranty" to live with and make the best of the issue.
Keep them coming,
Ponca City, OK
Currently Being ModeratedFeb 3, 2013 11:43 AM (in response to Ashadur)
Hello to everybody.
I have iMac 21.5" (was bought in June 2011) and I have the same issue for about 6 months. I'm using OS X 10.6.8.
I've noticed that blackout occurs when I try to watch video (even on youtube), work in iMovie or use other graphics software.
When I'm serfing Internet or listening to music all works well.
Hm.. Gonna try your advises.
Dmitry Isaichev (Moscow)
Currently Being ModeratedFeb 12, 2013 3:53 AM (in response to Ashadur)
Thought I'd post an update on my situation (and many of you won't like this I'm sure...).
Spent about a month around mid Dec-Jan speaking on and off to Apple but we couldn't directly diagnose the problem. Because my Mac isn't in warranty and I didn't have Apple Care I was out of luck.
I'd tried carefully monitoring temperatures, using fan control, using safe-mode, reinstalling the OS, etc. They all helped a bit but the problem always came back.
In the end I sent my Mac in for repair because I couldn't work on it any longer. I had the whole LCD unit replaced which cost £560 inc VAT (that's roughly 870 USD). This seems like the only realiable option if you are not in warranty. It might be possible to get cheaper LCD replacements though.
Hope you all have more luck.
Currently Being ModeratedFeb 12, 2013 4:05 AM (in response to marcdl)
Thank you marcdl for your hard work in this effort and for keeping us up to date with your testing. I too have come to that same conclusion. While others seem to have had luck going back to Mac OS 10.7 (LION), still others have not.
I am continuing to limp along using fan-control software, an external fan (when needed), and a very cool, darkened room (so i can run a low screen brightness). These mediations will most likely prove inadequate when our Oklahoma spring turns to summer and I am no longer able to keep the room adequately cool. I do know one thing: heat exacerbates the problem.
I am convinced that, at its root, this is a hardware issue (as you and others have proven by LCD backlight panel replacement). But it is definitely made more sensitive by heat. If those affected can manage to run the display at a lower brightness, use internal fan-control software, and an external fan when needed, they might be able to limp along for while as I am.
Thanks to all,
Ponca City, OK
Currently Being ModeratedFeb 17, 2013 9:42 AM (in response to Ashadur)
I've been having the exact same problem for the past two years. I have late 2009 27" iMac. I've been always happy with the quality product Apple puts out. Snow Leopard, Lion, and Mountain Lion, all didn't fix the issue. So far this forum has been the most helpful. I agree with the temperature affecting the blackouts. I read in some other post that it might has to do with the LED power board, and I got it replaced to a new one for $50, and it still didn't fix the problem. Having the screen brightness at low level definitely slows down the blackout issue. Apple must acknowledge this issue and should replace the defective iMacs.
Currently Being ModeratedFeb 18, 2013 4:41 AM (in response to shkang81)
Thank you for your post shkang81. Yes, it would be a big help financially for a lot of owners if Apple would declare this an engineering issue, as it obviously is, and do a repair recall. I suspect that since the problem is so expensive to repair (LCD backlight panel replacment) that few can afford it, hence there is not yet a red flag raised in the service chain. If anyone knows how to escalate this issue with Apple, Inc., and make our problem heard, ideas would be appreciated.
Ponca City, OK
Currently Being ModeratedFeb 18, 2013 4:44 AM (in response to isaichev)
Yes, isaichev, the problem is almost controllable as long as the processor is not heavily used. When I just do word processing or listen to music or surf the web, I can limp along with the fan control software, reduced screen brightness and the external fans. But when I crank up Aperture, Photoshop, and especially Final Cut Pro X, and the internal temps start to rise quickly, the issue becomes crippling.
A replacement LCD Backlighting panel seems to solve the problem. Unfortunately this is 1/2 the price of a brand new iMac!
Ponca City, OK
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