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

I know that I'm a bit late to this discussion, but for the sake of all people who will have this problem in the future, I'd like to share my experience.

I had the black screen issue as well, and cleaning those two LG connectors on the back of the screen didn't help me. And also it is not logical why would it help. Here's why it shouldn't - when one of the two connectors is faulty (bad contacts), only one side of the screen goes dark. So how would both of the connectors have the same issue at the same time (in the case when the screen fully goes dark)? So if you have the issue of the whole screen going black at random times - in my opinion, it is most probably NOT the 'LG issue' .

In my case it was (most probably) a faulty inverter board. I'm not sure what exactly was wrong with it. I'm almost certain it wasn't overheating, because my screen sometimes would go black a few minutes after startup. But after that it could work for weeks without issue.

After replacing the inverter board the issue didn't come back for a couple of months now, so I really hope that was it.

Friends, we seem to have solved the problem - for us, at least.

Where we started: Our son´s imac 27, black screen almost always, pram reset helped a little, as did the wakeup procedure as described by many. Changing the startup volume (external hd) did not help, nor using other systems. Running the hardware test (after pram reset) from disc kept the imac running without black screen all through the night but with the fans at full speed. This to us seemed to indicate a heat issue - although, as stated by others, the screen stays black right from the start i.e. even when the computer is kind of cold. Maybe some of the more knowledable of you guys can explain why the imac seems to collect its bad heat memories from the past - I guess until a pram reset is made.

We had this issue for more than two years and were about to sell a broken imac for little money. But then...

What we did: We opened the imac (for the first time, but not hard to do, enough information about that on youtube) and moved the lcd heat sensor to a place closer to the fans.

Well, yes, and that did it. For more than a month know, and for many many hours non stop.

No guarantee, no idea if we could have caused other serious problems by moving the sensor...

I wish you all luck!

I just went through this process with "MacProfessionals" (they are the regional Apple Certified repair center), and they told me upfront that replacing the backlight board might not fix the problem. It took them several weeks to get the backlight board from Apple, but finally they contacted me yesterday to come pick it up. They said it had run overnight without an issue. However as soon as I got it home and powered up it only took about an hour before the first blackout happened. :-( So, I am out the $200, but it was a gamble anyway. The machine is out of warrantee, and the cost to replace the (whatever else) is more than a used model on ebay. So that's my experience... YMMV

I've also this problem. Since some months ago, the screen of my iMac 27" Mid 2010 started to go black (off) randomly. I know the system is running without problems because I can put my computer in sleep mode (control+shift+eject), and after press a key to awake the computer, the image comes again always. After doing this, sometimes it remains on for hours, sometimes just for few seconds.

I can also work perfectly with another display attached, when the iMac screen goes black, the second display remains on and working. So, I can absolutely discard a graphic related problem.

I don't think it's software related either... because I've tried to start the computer with the Recovery partition, to reinstall the latest Sierra version several times (with the COMBO Update) and always I had the same problem. I've not tried to restore an old version of macOS, but I think it's not necessary... it should work fine with Sierra without problem.

One more thing... and this is curious: you can try to use the flash light of the iPhone very close to the iMac screen and look what happens! In my case I can see all the info there! It's difficult, but if you have a enough power light and you put it very very near to the screen, you should be able to see the icons, the windows, the images, the texts and everything of your desktop or your system running is there, but with the backlight switched off. You can test your computer to see if the same happens to you. In my case, I think it's simple: the problem is that the light of the screen (LEDS) is switched off.

So, I'm 90% sure it's a problem related to the LED DRIVER BOARD, also called the inverter... and sure it should be replaced. But any case, Apple should say something, because although all of our iMacs are out of warranty, I think it's not normal that so many iMacs having the exact same problem. Perhaps this models, after some years of use, start all of them having the same problem with this piece of hardware.

As an update to my original solution from Nov 25, 2016 - I continue to firmly state that the issue is 100% the connection on the LG display. I cleaned the connection and the screen worked immediately, with the results lasting for a few weeks. I would repeat the process every couple of weeks.

However, I got tired of this and eventually just replaced the screen as pbook4g5 did. I purchased a new surplus screen off eBay for a good price. Again, the other screen would display an image just fine when working, so it wasn't the screen but the connection to the screen.

I replaced the screen in January 2017 and am writing this 10 months later in October 2017. During this time I have had zero issues and the screen has worked 100% at full brightness for 10+ hours 6 days a week (it's my main work computer).

If you go this route, please re-read the posts I link to in my original post that describe the process to replace the screen. It's not just a swap and replace. You have to remove the bracket from the old screen - which is glued on really, really well (you have to take great care to not bend it).

Best of luck...and again a huge thank you to pbook4g5 for finding and sharing the solution.

We're having identical problems with identical machines. Very frustrating isn't it? The way I get my screen back on is hitting Control+shift+eject buttons all at the same time. This is the keystroke combination to switch montors from internal to external. Sometimes I feel like I'm playing a video game to keep the thing on when it starts shutting off every two seconds.

I'm resigned to making an appointment at the genius bar. What I've read points to the video card. I read a VERY involved message somewhere about a method of flashing a firmware update to the video card BUT it involved having Windows loaded in some fashion and was more time consuming than I am willing to do. But if they (Apple) swap the card, you'll end up with one with the new firmware and problem (supposedly) eliminated.

Glad I could help a little.

It's unpredictable. I had a good day on Friday and Saturday, now today it's back doing it again.

Mine has been doing this more and more for the last two weeks and finally got to the point where it runs for aobut 9 minutes and then quits!

However, it will then go on a spell where it will run for an hour and then something will start not working right, e.g., can't put something into the trash. I'll try to make it restart and it will crash,

I have also tested it by connecting a firewire cable between the 27"iMac and my 13" MBP with the iMac turned off. Then I turn on the iMac holding down the T key which lets the Hard Drive of the iMac be accessible on the MBP as an external drive. The iMac will show a screen saver and I can see the files on the iMac Hard drive. But then it will quit and the connection to it's hard drive from the MBP is lost at the same time.

When the iMac quits, the screen goes black. Nothing works, although I am waiting now for it to quit again so I can try the 3 button step mentioned above. However, if I listen very close i can hear the fan running inside and if I press and hold the power button, then I hear a 'clunk' and the fans go off. It will restart but is very slow in doing it.

Also, one time it quit in the morning when it was cool in my room and it had only been on for 10 minutes. The bottom of the back of the iMac was still cool to the touch and the top of the case was only slightly warm to my cheek so I don't think this is a heat problem.

Finally, there was a long discussion that evolved into the 15" MBP and concerns about Lion. I have Lion 10.7.4 (11E53) installed on it, my 24" iMac, my 13" MBP and on this older miniMac. None of the other 3 have any problems and all work solid. The 24" iMac is left powered on 24/7 for months at a time and puts itself to sleep when we are away from it but otherwise it is always on and no issues.

I had done the SMC and the PRAM resets to no avail.

I called Apple Service yesterday (6/23/12) and she had me check the HD which came back fine. While she was trying to get thru the rest of her tests, it failed twice! She told me to take it to a local Apple repair shop as I am >150 miles from the closest center which for me would be KCMO.

So, Steppy, you are not alone here and I will be sure to let the group know what I find. The thing I am most concerned about it they will keep it and say they found nothing and I am not interested in working on a computer that can stop without warning!!

C U All

Jim

One More note

It just quit after playing internet radio on iTunes for about an hour. I started copying some files over from it to an external hard drive via the firewire. Did a 250 MB set of files and all was fine. Started to open some other files to see if I needed to copy them over and it stopped with a black screen and this time was making a pulsing noise from the interior of the computer. It's the first time I heard this noise It was not the internet music still playing.

(As a complete aside, I was playing the same station on the 13"MBP and it kept playing the music.)

I then cycled the power off and the pulsing noise went away. I tried it restart and it took a long time to get to a screen but before anything could happen, it stopped and I had to hold the power button to get it to turn off. I restarted it and it made the chime sound but would not restart (Attempted Twice) and the screen stayed black.

I then pulled the power plug and reinserted it. It then came up with the white screen for about 5 seconds and then went black.

Maybe it has finally died!! If so, they should be able to figure out what has happened to it tomorrow when I take it in.

C U all

Jim

Here's an update on mine.

I drove 50 minutes to the Genius Bar today and, of course, it would not do the montior shutting off trick while I was in the store and it had been doing it (this very morning) to the point that it was nearly impossible to use. I get to the store and nada. Go figure.

Anyways... the genius gave me a course of actions to try to narrow it down as to the cause and eliminate some possibilities.

First, try making a new user account. If it quits doing the blacking out while using the second account, then it's something tied into the first account.

IF it continues to black out after making a new account, he suggested I reinstall Lion (not wiping the drive, just over existing install and this should leave all my personal settings alone)

If that does not work, he suggested I go into the disk utilities and wipe the drive then do a fresh install of Lion. If I restore anything from a backup to only get non-App files such as docs, pics, music. Manually reinstall all my apps.

And if it STILL continues to do, bring it back into the bar and leave it with them. It could take 1 to 2 weeks to diagnose and fix.

I got home, set the Mac backup and BAM, the screen was blacking out! Why couldn't it have done that at the Apple store?

I'm trying the new user now, I'll keep you posted as to the success on it.

Hi Steppy and others

Here is the update on my machine. I took it to the local Mac service center on Monday morning and aafter a few days I called and they told me they had just received the new Logic board and should have it in then or the next day but given the inermittent nature ( Which they had seen fortunately!) they wanted to burn it in. On Thursday they called and said that was not the problem and so they were changing out the Video card.

Friday just before closing time they called and said it seemed to be working OK there but for me to pick it up and let them know if there were any problems.

I got it home and now have a different problem. It booted right up and so I started iTunes to let it just play in the background but as soon as I started it, it started pixelating the screen. within just about a minute I had 7 noticable bands of pixels. Fortunately I was able to grab my camera and take a screen shot of it. The music continued playing that song although the time progress bar in iTunes quit updating and I had lost any mouse control. I had to power it off by the power switch.

I waited awhile and restarted it. It seemed to work just fine and I played quite a few songs on iTunes and decided maybe that first pixilation was just a fluke. I tried to start Parallels but found the change in the logic board had messed up my Parallels registration. While I was looking for the password stuff, I realized the machine was hung up and un responsive to the mouse and keyboard.

I rebooted and started something else but before I got going, the machine again froze with an unresponsive mouse and keyboard so I just shut it down and got it ready to return to them on Monday

An additional note, In every failure / hung situation, I never lost the screen as I did before and the mouse cursor would always continue to move, just no response to clicks on it nor any responses to Keyboard inputs.

Sorry for the long story, and even more that I don't have any real news to report - other than the screen is no longer going black! So maybe part of the issue at hand is the video card. What else is lurking remains to be seen and I'll let you all know more as soon as they do some more troubleshooting.

C U All

Jim