Previous 1 2 3 4 5 Next 281 Replies Latest reply: Mar 28, 2016 4:14 PM by Marjorie Freedman Go to original post
  • yvettegri Level 1 Level 1

    I had this problem also. My hard drive stopped working because of all the sudden stops without properly parking the drive. I had to reformat it, but couldn't get the operating system to load. The fine Apple Geniuses were able to load a system. I took it home and it immediately started going to black again.


    I did massive research on the web and solved the problem, and came up with a reason for the problem.


    The cause is heat. The SMC fan is not cooling down the system which is then shutting down because of the heat.


    There is a temperature sensor in the drive to supposedly prevent this. However, if you've changed your drive like I did, and replaced it with a drive that did not have a temperature sensor, thent he fan controll gets all confused, doesn't turn on properly, everything heats up and then shuts down.


    This also happens on factory installed drives when the temperature sensor goes bust. A lot of Apple's early drives for iMacs and MacBooks were really cheap and the sensor failed. I had to replace my factory isntalled drive because it failed. (Thank you time machine).


    The solution is a simple FREE software download called SMCfancontroller that turns your fan on at specific RPMs, and turns it off when you aren't overheating. I installed the software and haven't had a "go to black" moment since. The software can be downloaded here:


    There is also another fan controller called Ultrafan which is also free.


    There is a paid fan controller, but you don't need it. the free ones work exactly the same. The paid fan controller gives you a 1 HOUR DEMO, which is not enough to evaluate whether or not it works.


    BTW if you drive has failed and you have a time machine backup, which backed up before upgrading to Mountain Lion, DO NOT UPGRADE TO MOUNTAIN LION until AFTER you've restored your time machine backup. Install Lion first, do your time machine restore and then install Mountain Lion.


    I found out the hard way that Lion time machine backups are not recognized by Mountain Lion.


    Hope all this helps.

  • Stepppy Level 1 Level 1

    Your problem is not the same as mine.


    When my screen goes black, the iMac doesn't shutdown and the drive doesn't go off.  Its literally the backlight which is going off.


    I can log into my iMac using Splashtop streamer and carry on working even though my screen is black.


    Once the problem is consistently bad I will take it in, but at the moment its very sporadic.


    Thank you.

  • Stepppy Level 1 Level 1

    Latest update.


    Finally my screen problem got worse to the point that only the right side was illuminated fully and the display started whistling.


    As I didn't want to be without my iMac for a moment longer than needed I booked a genius appointment at my local Apple store for Saturday morning to discuss my problem.  Rather lug it in I took a photograph which I took of it starting up with the Apple logo as that showed brilliantly how the screen was only half illuminating.


    The guy at the Genius Bar knew immediately what my problem was from the photograph and my description of the other issues.  He said it is a known problem on the 27" iMacs and they always keep in stock a new improved LCD & Backlight kit.  He didn't need to see my iMac to do any testing and just said to bring it in and they would do the repair.  I took it in the next day (Sunday) and got it back yesterday (Bank Holiday Monday).


    Pleased to report that I now have a fully functioning iMac.  I can't believe how much better the display is after putting up with a problem one for so long.


    Incidentally, I had just 6 days left of my 1 year warranty which is a good job as otherwise it would have cost £440.  I did buy the Applecare extended warranty about a month ago, so that is definitely money well spent


    Hope this helps for anyone else with this issue.

  • EnderCF32 Level 1 Level 1

    Awesome suggestion!  That fixed the problem for me.  Now I just have to figure out how to get Lion back on my computer without repurchasing everything =).  I just talked to apple about my journey, and they didn't give a rats ace about the problem, or at least in helping me get back to my previous OS (right now I'm stuck with Tiger).  NOT IMPRESSED APPLE!!!  Thanks guys for the help in getting a fix.  It's weird because the fan app that I downloaded said that my computer's temp is -197F, so I think that's what my computer was doing, it was self preserving.  Glad to have a fix.

  • Berniedmj Level 1 Level 1

    I know it is a late response but, i have the similar problem. But the difference is I bought mine less than 4 months ago!? It's a late 2011 27 in. model. I brought it to the genius bar yesterday & they called me today that saying it passed all their test. My friend said that apple doesn't have any true "technician" at the store because they'll just hooked it up their system & run a diagnostic without them doing any hands on stuff?!? Meaning, they didn't open it up to see if their might be a loose connection or a short.  In any event, they said they played all my HD videos via iPhoto (which I didn't care) & played HD YouTube vids. They said they let it play all night or whatever & no black screen. So I have another appointment with them tonight & I asked them if i can  try to replicate it (hopefully)!!! They sure! So let's see what happens

  • ricardoh123 Level 1 Level 1

    27in Imac 3.1 Ghz intel core I5 screen goes black


    I have the exact same problem, so frustrating. I took my Imac into the apple store and they said they couldn't reproduce the problem.


    I found that if i turn my screen light down to the dimest setting it stays on without any issue. With full brightness it can happen every 30 seconds, though it is still unpredicatable. When it happens, the computer still runs playing songs etc. I have to tap my power botton to get the screen back up again.


    I feel apple needs to take responsibity for this problem. Its not fair that people who pay over 2000 dollars for their product have to be jerked around. I have read countless post where they can't reproduce the problem then send you home with some bogus trouble shooting solutions. If this many people are having the same problem, it needs be addressed.


    I hope we all can find a solution for this problem!!!

  • yvettegri Level 1 Level 1



    The problem is overheating. This usually starts if you have replaced the harddrive. My original harddrive was one of the really cheap Chinese ones that Apple had purchased with a high failure rate. They were crap. I replaced it with a great 2 terrabyte drive. Unfortunately after I replaced it I started having the going to black and shutting down problem. If you have the original harddrive it might be that it is working, but the temperature sensor is no longer working. I'd recommend you replace the harddrive, also. I bought my 2tb drive from They are a great site. There are youtube videos that will walk you through replacing your harddrive, step-by-step, unless you have a local fixit place. Apple will not replace them with drives they don't sell.


    The original harddrive had a temperature sensor that told the fan when to spin to cool everything down. Without that sensor the fan misreads the temperature and shuts the machine down. BTW this constant shutting down and revving back up is not good for your drive.


    There are several solutions.


    Solution #1: Try a free software program called smcFanControl. Here's the url:



    Solution #2: If that doesn't do the trick you can buy a more robust fan controller for $29.95. Their site also has a complete explanation of what is happening:



    Solution #3: Go to amazon and search for small desktop fans. Buy a really small one and just put it on your desk behind your MAC and run it to cool down the back of your Mac. That will also work.


    It is a heat problem. I'm surprised that the people at Apple don't know this. I find that as long as my iMac is running at 52°C I'm fine. But once it gets to 54°C or more, it starts going to black and shutting down. Then when the fan spins down I can click on my mouse and it'll start back up and I'll be find for a while.


    Like many of you, I took my iMac into the Apple store also and they couldn't replicate the problem because the store is airconditioned and the machines don't often get above 54°C. So they aren't going to shut down.


    I hope this finally solves the problem for you guys. I know I was extremely frustrated. If it doesn't solve the problem don't hesitate to contact me at


    Good luck. -- Yvette

  • Berniedmj Level 1 Level 1



    If you still have the warranty... use it!!!  I did.  It saved me a lot of money!!!  Roughly $1000.00!!! 


    OK.  If you have an iPhone/iPad, record the issue, try to replicate it again and then show it to them!  It's way better than explaining what the **** is going on.  A recorded video is considered a documentation.  (This is a continuation from my 1st post above)  During my 2nd appointment, I've tried everything to replicate my issue and... No issues.  They did another diagnostic, passed with flying colors, and I picked it up the next day. 


    I hooked up everything at home and then after an hour or 2, the same thing happened?!?  My screen went blank with the music/email notification sound/volume going up or down still sounding off. I recorded everything on my iPad from turning it OFF to ON to doing the normal stuff I typically do.  In this case, watching Youtube.  I was unfortunate yet, fortunate to replicate while recording it on my iPad because it happened again and again. 


    Long story short  I visted the genius bar a total of 9 times to resolve this issue!!!  I complained about it & it went all the way to corporate customer relations. 


    Long story SHORTER, they replaced my video card, the mother board, & the monitor.   My computer is working fine.  No more blank screen with sound. 


    So the only issue (which happened 2 times so far but it's not a huge issue) is... I get these different color prints on my screen & then it freezes.  The best way to describe these prints is like... removing a adhesive tape from a screen but the adhesive is still on the screen.  I don't know but that is it.  


    So use your warranty & record all issues!!!!

  • ricardoh123 Level 1 Level 1

    wow, 9 times, thats insane. Sounds like they should have just given you a new computer : ) I use mine a lot for work. Its hard to leave it there for a week while they wait to replicate the problem.

    Great idea to record the problem happening to have documentation. My  computer is only covered for another 4 months so I really want to get this sorted out.

    Does anyone know what their policy is for a defective product? Like at a certain point are you entitled to just get a fresh computer? Seems fair enough, thats a lot of your time to be wasted driving and waiting.

    thanks for the reply

  • ricardoh123 Level 1 Level 1


    my computer will never go to a black screen if my light is at the dimmest setting, that's telling. Overheating maybe, but the computer's hard drive doesn't shut down, only the screen light. I can still use my computer with my mouse just no clue what Im doing

    Also this happens even when using my computer in a really cold room.

    It seems like the LED light over heats maybe?


    so far Ive read a lot of fixes

    logic board

    power supply

    stuff running on bus power

    over heating

    I wanted to put this out there so we can all find a solution.

    thanks for your reply

  • Berniedmj Level 1 Level 1

    i honestly thought i was going to get a new computer but i just wanted my computer back. Reason being, when i first turned it in, school was about to start less than a week.  When I turned it in the 4th time, i asked them if they can expedite it since school already started.  They said, "yes and it'll be ready tomorrow morning."


    The next day I went to class and called them around 1pm and inquired about the status since I didn't get a phone call.  they simply told me, "we'll call you when it is done."  I told the rep that they said that my computer was supposed to be done in the morning today! The rep transferred me to a technician.  The tech told me that they're doing a diagnostic. I asked how long will that take? He told me hours or even DAYS!!! I was cool with that and let it slide.  But i was curious on "how long does it take to do a diagnostic." 


    Originally, all i wanted to know is, "where are they at with my computer?!?" Now I'm researching by making a phone call to apple support.  I asked him and told him, "the apple store has my computer. How long does it take for them to do a diagnostic once it is connected to their computer system?"  He said, "AN HOUR but definitley in a day!"  I told him that the tech said it takes days!!  the apple support guy told me he was lying!!!  Now I'm super furious!!


    AND that's when I've made my complaint based on the fact that he LIED to me.  


    Corporate customer relations made sure that my computer was getting top priority despite the fact that the tech at the store couldn't figure what's wrong with my iMac.  But hey!  I got new a video card, motherboard, and a new monitor!!! 


    In any event, video recording is best for documentation versus providing the symptoms based on hearsay.  you can be super illiterate about computers but, if you show a video of what's wrong, they'll automatically know what's wrong with  it... supposably


    Yup!  9 times visits.   9 times means


    1 time = drop it off for random going to sleep/black screen while using it but you can hear the music or video you're watching.

    2 times = picking it up  despite passing the diagnostic "with flying colors"  that's what they told me.  same issues happened again at home.


    3 times = appointment; trying to replicate but couldn't. went back home... got the black screen again and VIDEO RECORDED it.  They said that my outlet may not be giving enough power. I tested my outlets and there's enough power


    4 times = drop it off and showed the video

    5 times = pick up.  New video card   Black screen again and video record


    6 times = drop it off and showed the video

    7 times = pick up.  New logic board      Same issue  and recorded it


    8 times = drop it off and showed the video

    9 times = pick up.  new monitor and everything is working fine!!


    despite having to go there 9 times, I saved a lot.  I said, "$1000" from my previous post.  Actually, $1375.00!!!  And that's including labor.  you have the warranty, use it!!  why spend the cash to get the parts and trying to hook everything up yourself (if you have the tools, equipment, knowledge, and labor) or paying somone to hook it up?!? 


    But then again... I don't know how long you can live without your computer.


    Hey!!  since it is overheating, try vacuuming where the fan ***** up the cool air!!  it is located on the back just above the power cable.  the air intake looks round. It might be clogged with dust.

  • SkinnyStudios Level 1 Level 1

    $1375.00 Oh no!!!


    My imac 27inch (3.1 GHz Intel core i5) is 2 years old, I am Flexi-renting and still have another 2 years of payments, and you guessed it - out of warranty with no Apple Care left :-(


    I am having the same issues with the black screen, computer and fans still running, if I leave it on the black screen, it will come back after about 30min to an hour when I tap the mouse or press a button.
    It seems to be getting worse (more frequent) daily.


    When it first started happening it was a really hot day, and the back top of my machine was scorching, however, I don't think it is heat related as now it often happens while the machine is still cool.

    I thought maybe it has something to do with the sleep function?

    That, or it is the dreaded logic card / Back light / LED replacement option.


    I have tried playing around with the sleep and resolution settings in preferences, hoping to fluke something.


    I installed the smc Fan Control, it seemed to do something for a while, but the the issue started up again.


    I read about a firmware update to stop imac 27's flickering, thought it might be worth a shot - But when I went to install, my computer informs me that it is not needed, and wont let me continue.


    I am a Graphic Designer, I need my computer to earn a wage, it is very frustrating and upsetting to pay so much for what I expected to be a reliable machine, just to be lumped with a lemon.


    I have already had to have the HD replaced in mine, and spent $700 on tech's.


    I have been so happy with all my previous mac's but this one has been nothing but trouble -


    Has anyone had a response from Apple as to what is causing issues with the imac 27's? And how we are supposed to go about finding a fix? Please post if you have an answer or any advise you think might help at all.




    I never dreamed I would say it but... Maybe it is time to explore other (PC) options? eeeek!


    Good-Luck to all struggling with the same issue. I sympathise!

  • pbook4g5 Level 1 Level 1

    Well I'll add my two cents here since I'm also dealing with this same issue (27" iMac 2.66 i5 Late 2009). A couple of months ago, my machine turned itself off (or so I thought it did). In reality, just the screen went off, so I restarted and it came back. Fine for a couple of months. Then I thought... hey, I should research why it did that...


    That's when I found these threads. And literally, almost as soon as I clicked on one, the screen went dead again. iTunes was still playing, and I was still getting external video to my secondary monitor. I read somewhere asking if I could see a faint image on screen by holding a light to the lcd at an angle... yep, image was there. So, I confirmed the backlight had gone off.


    So I did some searching. My machine started going dark every few minutes (and the machine wasn't warm at all... it was cold). Sometimes a PRAM zap fixed it for a few days, but eventually it got to the point where there backlight was shutting off a few seconds after startup.


    After reading EVERYTHING in this thread, and tens of others, I thought the first logical step was to replace the LED Driver board. Found a seller on eBay selling new, OEM Apple boards for $52. I bought one. Installed it. The old board did have some slight discoloring on the soders near the power connectors, like they were slightly cooked... I thought that was interesting.


    Machine ran fantastic for about three weeks. Zero issues. Well, the issue is back again. I've got a thirty day return policy with this part so I inquired about another one.


    In the meantime, I thought the next logical step was to replace the LCD panel since the LED backlight is integrated with it. So, I ordered a used panel for $100 (I stole it using eBay's make an offer option). I ended up getting it from the same seller of my backlight board. So, he shipped them out together. They should be here Wednesday.


    From everything I've read, you replace the LED driver board first, and if that doesn't fix the issue, replace the LCD panel.


    IF that doesn't fix the issue, then I think my next step will be the power supply itself, since thats what's driving the LED driver board. Hopefully I don't need to do that, though. I'll keep everyone updated. Such an annoying issue.



    *My fallback is to just buy a nice(r) external display and mirror them and use the imac as an overgrown computer with a dead LCD.

  • yvettegri Level 1 Level 1

    I responded earlier about a free fan controller. However, I've since found that springing the 29.99 for the paid HDD fan control solved the problem for me.


    The problem is that your iMac is either heating up, or thinks it is heating up. When that happens the iMac shuts down. My problem started after I replaced a defective hard drive. The hard drives that come with iMacs have a built in heat sensor. When you replace your hard drive the machine doesn't regulat the heat properly. And sometimes the heat sensor just breaks.


    The HDD Fan Controller solves this problem completely. Ever since installing it a while ago my iMac has not gone to black once.


    You can purchase the HDD fan controller at:


    They have an indepth explanation on what is happening to cause your iMac to shut down.

  • pbook4g5 Level 1 Level 1

    Your information is not relevant to the issues that are being presented in this thread... most of the users here don't actually have their iMacs shut down on them... only the backlight goes off. The computer is still on and functional.


    I don't have any fan noise, and my hard drive is fine and its never been replaced. Your pushing a product that doesn't have anything to do with our issues in this thread.

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