Stepppy

Q: iMac 27" Screen goes black repeatedly, but then settles for a while?

Hi

 

I have searched and found numerous posts which sound similar to mine, but none seem to be so bad. Its a long post, but I want to make I have given as much information as possible

 

My Energy Saver settings are default 10 minutes for display & computer sleep, but I always find the screen will go black for a period of time before it goes to sleep and normally when I go back to it I press the keyboard or trackpad and the screen comes back to life. However, this time it didn't. I tried everything I could, but in the end I had to hold down the power button until it turned off. Once I restarted it was ok again.

 

I didn't think much of it, but I researched and found lots of people had similar issues, but were mainly on MacBooks. I did find a post where people had set a hot corner to turn the display off, so if the problem happened again they went into the hot corner and then came out of it and the display would come back on. This stops the need for having to force the computer off. I set up a hot corner, just in case it happened to me again and I'm glad I did.

 

In the last couple of weeks the display has been going off at random whilst I have been using it, nothing graphic intensive, just web browsing. Going into my hot corner and coming out of it bought the display back to life thankfully. It was yesterday that things got really bad, to the point that the display was staying on for about 3-4 seconds before going off. Again, going in & out of the hot corner worked, but then it didn't. Initially I thought it maybe some kind of software issue, but when I restarted the grey screen would only show for about 3 seconds and then go black, so I didn't even see the Apple logo. I could hear everything start and it would pause at the logon screen. Going in and out of the hot corner several times finally gave me enough time to login before it went off again.

 

After logging in I got it back only for it to go off again. I tired everything I could to get the screen to come back to life but it didn't want to play. All the time everything was working on the iMac, it wasn't frozen and didn't crash, just no display. I did some research on my iPad and this seems to be a common problem in one form or another, but no one that I could see had it as bad as mine. Some people were saying it was software related, other that it was logic boards, but as I said earlier I think the majority of posts related to MacBooks and not iMacs.

 

This was my first Apple purchase and I feel like a fish out of water as I have always had PC's before and if they went wrong I just fixed it myself, but I don't think this is going to be the case this time.

 

Very late last night I managed to get the display on long enough to run iBoostUp and let it give everything a spring clean. It kept going off whilst it was doing its things, but I did manage to get the display back for long enough to shut it down fully and I left it unplugged over night.

 

It started working fine this morning, but after more reading I have reset SMC and PRAM as that advice seems to be given a lot when people are having problems.

 

I have been using it for roughly a couple of hours and it has just this second gone off for the first time. I did my hot corner trick to get it back, then about 3 sends it went again. Now it seems to be ok again. The only program running is Safari.

 

I am running Lion 10.7.4 with all updates done and I am not running Boot camp for Windows 7 I thought about doing a clean install, but I am not convinced that is going to work and don't want to go through all the hassle of that only to find it still does it! Taking it to Apple worries me, because as its intermittent it may not do it whilst they have it and also I am worried about all my personal data I have on it. Would they wipe the hard drive and would they access my files? I have never had this worry before as any PC problems I just switched problem items myself. The machine will be a year old in a couple of months and I am already thinking the AppleCare Protection Plus is a very good deal and a must have at £139 for two extra years warranty.

 

Any suggestions great fully received.

 

Thank you.

iMac (27-inch Mid 2011), Mac OS X (10.7.4), 12GB RAM 1TB, AMD Radeon HD 6970M

Posted on Jun 24, 2012 5:44 AM

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Q: iMac 27" Screen goes black repeatedly, but then settles for a while?

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  • by jrthurm,

    jrthurm jrthurm Jan 21, 2015 3:40 AM in response to redbudgee
    Level 1 (0 points)
    Jan 21, 2015 3:40 AM in response to redbudgee

    Great observation, thank you, redbudgee. But Yosemite is already running on our iMac 27/mid2011, and the issue we all decribe arose while using Yosemite. It also arises with bootcamp. It even has arisen (on bad days) during the startup process even before the apple appears on the screen. So: It is probably not Yosemite itself that fixes the problem. But maybe reinstalling the system or installing a new system has a similar effect like SMC?

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 21, 2015 9:36 PM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 21, 2015 9:36 PM in response to Ulli Hesse

    So, I opened the Imac to see, if any Dust is in there und there was some, but not that much, I was hoping to find. Anyway, I cleaned him with a can of compressed air. I put the power cable for the backlight driver out and in again. Every board in the Imac i blowed, of course the fan´s as well and the cooling rips. When opening, I had to pull out the V-Sync cable, which was not in a good shape, but I hadn´t a new one. When closing the Mac, I tried to put the V.Sync Cable very deep in the slot, which succeeded hopefully without further damage,

     

    Results:

    1.) The HDD temperature sensor now increases only to max of 51 degrees, when using the Imac for hours. Before, it went to 57 degrees.

    2.) Until now, there was no screen blackout, but i didn't stressed the system that much, only normal use of Safari and so on for many hours.

     

    I hope, I will never see the black screen again and try to post the long term results in one or two weeks.

     

    btw: I don´t really think, we have a software issue, in my opinion, it is clearly a hardware issue. I use yosemite 10.10.1, when the black screen appeared.

  • by redbudgee,

    redbudgee redbudgee Jan 22, 2015 1:17 AM in response to jrthurm
    Level 1 (0 points)
    Jan 22, 2015 1:17 AM in response to jrthurm

    Thanks for your reply jrhurm,

     

    Thats a shame. Out of interest. Did you do a complete wipe of your hard drive and install Yosemite? Im just listing all the details as it might help define the issue. In my case, thinking back this might have started when I installed Mountain Lion and continued after updating to Mavericks. For Yosemite I did a full reformat and install from USB. Im only mentioning this as maybe (and take this with a grain of salt as im not an expert at all) whatever .kext file or driver is helping this is only replaced on a full reinstall. Is it possible that the hardware still references some OSX /Apple drivers or software even when bootcamp is running Windows? Again a long shot as this is well past my knowledge.

     

    I used the iMac all day today again with photoshop, indesign and illustrator and had no black screen. Windows black screen indicates it is hardware. Im certainly not convinced it is fixed though but it is most definitely improved. Previously about 10minutes was the best I would get.

     

    Maybe there are multiple hardware issues here which would at least explain why this is so hard to pin down to one component. I will continue to update anyway.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 23, 2015 2:41 AM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 23, 2015 2:41 AM in response to Ulli Hesse

    Yesterday, it happened again, black screen.

     

    - screen got bright aber waking up via active edge for only about 2 Seconds max

    - restarting and shutting down the Imac didn´t help, black screen in 2 Seconds after start

    - screen was alive when the backlight was set to the two or three lowest brightness levels and waking up via active edge

    - resetting the SMC did help! After the reset and startup of yosemite, problem was gone

     

    What does that mean?

     

    - SMC defective?

    - defective kext (device driver) for the SMC in Yosemite or because of corruptes kext by upgrading from snow leopard?

    - defective kext (device driver) for the SMC in Yosemite, because Yosemite´s kext ist faulty?

     

    When the Imac is in the problematic situation of black screen, you get always a bright screen when waking up or when the system starts (even, when ist lasts only für 2 Seconds, but there is always brightness for one moment)

     

    If this would be a hardware-fault in the screen or the backlight in the screen, that wouldn´t happen this way.

    I even don´t think, in this case, I have a faulty backlight driver board.

     

    In my case obviously, there is something wrong with the SMC ot the SMC-Driver, that manages the backlight.

     

    I started with the original snow leopard DVD in the situation of black screen and I saw with a flash light the installation screen.

    So it used the old kext for the SMC from snow leopard.

    This would mean, when the problem is with SMC kext from 10.6 and 10.10, then it is not a kext fault.

     

    It may be a hardware SMC problem. I don´t know, why the SMC sometimes must be resetted. Maybe, it is to old, or the data ist gone. Is there a battery on the logic-board, that is faulty, so that the SMC memory is lost?

     

    Otherwise, SMC maybe can´t be replaced with a new one, only the complete logicboard should be replaced.

     

    Not easy to find the fault. Maybe I just reset the SMC for the future, wenn it is nescessary.  Like bump starting an old Volkswagen

  • by jrthurm,

    jrthurm jrthurm Jan 23, 2015 2:57 AM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 23, 2015 2:57 AM in response to Ulli Hesse

    Ulli, thank you, precise description, and i find everything exactly the same with our iMac 27/mid2011. I did the SMC reset a couple of days ago (four resets in a row, even). While that had made the problem disappear successfully for more than 48 hours running time with screen on, when I did it two weeks ago, it did not help that long this time. The screen always goes dark again after a certain while (but not after seconds, as experienced before).

  • by Chicago Dude,

    Chicago Dude Chicago Dude Jan 23, 2015 9:37 AM in response to Stepppy
    Level 1 (0 points)
    Jan 23, 2015 9:37 AM in response to Stepppy

    I have a solution that worked for me!!  But first some background.

     

    I have been dealing with the screen on my iMac 27" (Mid 2011) for several months now.  In the beginning it would randomly just go dark and I could not get it to come alive without shutting it down and restarting.  I soon realized that it was only the screen that was shutting down, since certain key strokes produced a sound (e.g., command-shift-escape).  So then I found that if I clicked the power button a few times, then I would get the logging on screen.  I reset the PRAM, etc, but no help.  I called Apple support and they recommended fixing everything in Disk Utilities (permissions, repair disk), but that did not improve things.  I was then using Mountain Lion and they strongly recommended updating to Yosemite.  I eventually did but things actually got worse.   I changed my security setting to "require password after 1 minute" so that I would not have to log in after every dark screen episode. 

     

    After reading many blogs, there was much discussion about heat being the cause.  While the screen was bright, I put my hand over the vents and found that every time I put my hand over the middle part of the screen (back of the iMac, near the top), the screen would go black within a few seconds.  Clearly, blocking the airflow raised the temperature sufficiently that it caused the system to shut down.  You should try this!

     

    Solution:  As suggested by someone in one of the blogs, I installed "smc Fan Control", a freeware utility that allows you to increase the default fan speed for the three fans that are evidently in the iMac.  The utility showed that the internal temperature of my mac was 49 °C (120 °F), which seems quite hot.  I set the speeds of the three fans to ca. 2000 and within 15 minutes the temperature had come down to 39 °C (102 °F), still warm, but much better.  Since doing this, the computer has not gone dark on me.  I should note that even at this temperature, if I block the central part of the vent slot with my hand, the computer screen will go black within a few seconds.  So, as long as I don't do this, I can now use my computer without the dreaded black screen.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 24, 2015 2:01 AM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 24, 2015 2:01 AM in response to Ulli Hesse

    Again black screen:

     

    What I found out:

     

    - in black screen situation even a clean install from USB leads to a black screen, so no kext problem

    - in the situation, the Preference Pane for Monitor has no brightness control (saw via vnc on a Macbook)

    - this time, the SMC reset did NOT work. Maybe heat makes the black screen effect worse and the SMC Reset did only cool down the iMac a little, so that the effect did not appear afterwards.

     

    Now I try the fan Control again and turn the fans to 1500 rpm.

    Maybe, this helps

     

    The Question is: what exactly is damaged? The answer helps find out the costs and if it is worth. Logic board and backlight a few hundred euro. But, if this did not help? Apple itself would probably don´t find the exact solution and is much too expensive.

     

    Very very difficult.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 24, 2015 4:43 AM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 24, 2015 4:43 AM in response to Ulli Hesse

    Hello,

     

    did one ever cooked a backlight driver board in the oven, just like some do with their graphics cards to repair?

     

    Maybe, this could help?!

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 24, 2015 6:13 AM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 24, 2015 6:13 AM in response to Ulli Hesse

    I bought a used backlight driver board.

    I will tell you the results in a month or so.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 24, 2015 12:58 PM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 24, 2015 12:58 PM in response to Ulli Hesse

    Just one short information:

     

    since some hours, i have the black screen situation and i can work with low level of brightness.

    When increasing the brightness to more than 4 blocks, the screen blackouts after a few seconds every time. PRAM reset, SMC reset, Shutdowns or Restarts do not help.

     

    In system preferences in the monitor settings, for testing purposes, I just put the brightness slider very very fast (almost like crazy :-) in all possible positions for about 30 seconds to bump the backlight driver board a little.

     

    Now, I have the brightness at about 65% for some minutes, which wasn´t possible before. Of course, because of the hardware issue, it will blackout again, but maybe, this is an new or helpful information for someone. I don't know, if this behavior is reproducible, I will see. This is of course no real solution, i wait for my used backlight board. I will replace the v-sync cable as well.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Jan 28, 2015 10:31 PM in response to Ulli Hesse
    Level 1 (0 points)
    Jan 28, 2015 10:31 PM in response to Ulli Hesse

    Sync cable and backlight driver board replaced.

     

    and voilá

     

     

    Black screen again.

     

    Damned

  • by jrthurm,

    jrthurm jrthurm Feb 1, 2015 7:02 AM in response to Ulli Hesse
    Level 1 (0 points)
    Feb 1, 2015 7:02 AM in response to Ulli Hesse

    Strange all this. This night the iMac was running with the screen on all night through (10+ hours), no problem. Without smc reset or anything, it just was more stable for no visible reason. But, VERY STRANGE: When I entered the room this morning, the screen went black on the spot in that very moment. I did neither touch the mac nor move the mouse, did not even come closer than a meter, the room´s floor does not vibrate or anything... I only turned the central heating down in the iMac´s room and will have made the air move a little ... (but no temperature change in the room temparature that fast, I can ensure you...). SO: What does that mean?! Either nothing and this was just a strange coincidence. Or: I am part of the problem... ;-)

     

    Well, the problem can also arise while I am away, so I must not become superstituous.

     

    BTW: I woke the screen up with the usual procedure. And: Covering the upper fan slots with one hand does not make the screen go black in our case. So even when I am assuming that something in the depths of the iMacs hard- and software seems to be in a very unstable state: I don´t know yet what triggers it.

  • by jrthurm,

    jrthurm jrthurm Feb 1, 2015 7:04 AM in response to redbudgee
    Level 1 (0 points)
    Feb 1, 2015 7:04 AM in response to redbudgee

    Hello redbudgee, sorry for being late with my answer to your question: No, we did no clean install but only updated the system.

  • by Ulli Hesse,

    Ulli Hesse Ulli Hesse Feb 4, 2015 11:18 AM in response to jrthurm
    Level 1 (0 points)
    Feb 4, 2015 11:18 AM in response to jrthurm

    Maybe, i am to early, but I think, the problem in my case is solved.

    I have done a clean Install with an USB stick made with disk maker x with yosemite 10.10.1) on saturday.


    - start the Imac with the alt-key and choose the USB stick.

    - When the installation program is displayed, chose the disk utitlity and format the whole harddisk.

    - install osx 10.10.1 on the clean HD


    First installation attempt failed, the imac froze. I really don´t know, what happened, maybe the system detected the replaced backlight board, that did not solve the  issue (blackouts backlight) and did a firmware update or something. I am not sure. I had to power down the imac and start again.


    The second time, the installation via USB was fully successful. Interesting: the email programm now has labels under the icons.

    This wasn´t the case, when I updated from 10.6.2 to 10.6.8 and to 10.10.1


    So i knew, something was changed by the clean installation of yosemite.

    Because of that, the last hope: I did a long term test through the whole night until the morning with energy saving settings off and screen saver off.


    My imac never was able to have a bright backlight after that, but now, it did it.


    So the long term test went on. Sometimes, I did a restart or a went to standby. My girl friend used the imac even für work for hours and every evening, I used the Imac for many hours.


    The blackout since saturday never appeared again.

    I have no active edges or temperature monitor running.


    Very strange: when I tried to do the clean installation a few days more ago, when the Imac was in the blackout stage, the backlight even went off when starting with the usb stick.

     

    One of the following steps must have solved the issue:

     

    1.) clean install by the usb stick

    2.) the replaced backlight board in combination with 1.)

    3.) the replaces v-sync cable in combination with 1.)

    4.) 1.) +2.) +3.)

    5.) maybe cleaning the internal parts of the Imac from dust with compressed air helped as well, because the hd temperature sensor only goes up to 51 degrees (before cleaning 57 degrees), though the Imac was´t very dusty

     

    Just one information: after replacing the backlight driver board and the v-sync cable, the blackouts were few, but they were not gone.

    Only the clean installation did it, but maybe, it wouldn´t be possible without replacing the the mentioned parts.

     

    So maybe, the clean installation can be successful, but I don't know, because I did it, when I already replaced the parts.

  • by jrthurm,

    jrthurm jrthurm Feb 4, 2015 12:36 PM in response to Ulli Hesse
    Level 1 (0 points)
    Feb 4, 2015 12:36 PM in response to Ulli Hesse

    Ulli, I wish you luck! Keep us informed, if anything happens...

     

    What your solution would not explain is the fact that the same problem also can arise using bootcamp, right? Or are there some basic software parts/drivers etc. used by OS X and Windows in common, which could have been updated by your clean install? Being no specialist I have no clue.

     

    I myself tried something completely different: Two days ago I simply removed the cover-grid from the downward opening where the memory is installed, and where the air is drawn in in by the fans. Assuming that a bigger opening would have positive influence on any temperature issues, just in case temperature is involved in our problem. And indeed: the computer is running smoothely since, for many hours, except one single black screen, hm.

     

    I have no smc fan control installed yet, so I have no monitoring of the actual temperatures, sorry...

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