iMac screen goes black, but system runs fine in background

Late 2009 iMac 27". SOLUTION: I'm reverting back to Snow Leopard.

History: The black screen happened when I first opened my iMac back in December 2009. After six months and many complaints by thousands of iMac users, Apple finally released a firmware update that fixed the issue. My iMac worked great until I upgraded to Yosemite a year or two ago (ugh, and I knew I shouldn't have done it!!!). The black screen was sporadic at first and progressively got worse. After the latest El Capitan update. I can't get the screen to stay on for more than a second now.

This morning, I booted up Snow Leopard from my external HD.
Viola! No more black screen. So it appears to be another firmware issue, just like the one Apple had all the way back in 2010, but now it's happening with the newer operating systems. I hope Apple fixes it. I really don't want to go back to Windows and PCs. I definitely prefer Apple products overall.

I don't believe all of these are heat issues as mine will do it from stone cold. I tried altering the brightness and the problem went away. YAY! 5 weeks later . . . it's back and altering the screen brightness has no effect. I've done a clean out (not a lot of dust though), I also have an aftermarket fan speed controller set at higher speed and accelerating sooner. Looking for a new idea now.

Just Wondered has anyone else has their mac setup with duel boot into windows? When I run from windows I don't get the black screen So this tells me It is not hardware related ie it's not over-heating, or keyboard or loose cables or backlight etc but a software glitch in the mac os. I can run all day in windows but when running on Mac platform I'm lucky if the black screen only comes up a dozen times in a day's work. Thank goodness I have a second screen. I'm running a late 2009 27" i5 with 1 Tb SSD and 32GB Memory. No problems when I run in Windows 10 only in Sierra

I'm still running El Capitan.

I might update to Sierra and see if it helps. Have been reluctant to as I'm still using the original 4GB RAM and wasn't sure if it would turn my machine into a brick in mud. 😕

MY problem started sometime after I installed Sierra on my mid-2010 27" iMac. It's usually after working for 4 hours. Keeping the brightness below 1/2 helps. I will try the TG pro software and turning off automaitic brightness. It has to be software or sensor related.

Very interesting. Mine is also a mid 2010 iMac 27" and yet my issue seems (so far) to have gone when I upgraded to Sierra. Been about a week now without a black screen but too soon to consider it an absolute solution. As expected, a noticeable sluggishness has resulted from the upgrade. Time I upgraded the RAM I think.

I Don't have a display settings that looks like that; maybe you aren't using the same model iMac.

I Installed trial version of TGPro and was able to work for three days with higher brightness, all the way to 100%. But now this morning it's going black again after about an hour of work. Fan is not running, temperature is well below normal. This is very annoying and is costing me time and money!

I will call Apple again.

Hi, Michael, the settings I showed are found under Accessibility in system preferences then click on display in the left-hand panel. I haven't done a complete rebuild yet but I have reinstalled sierra again manually and I have not had a black screen for 5 days I didn't touch any of my other settings that I mentioned in the previous post and have been doing some fairly heavy video and audio work for up to 8hrs at a session and all seems to be working.

Thanks Gomoweb. I should have just reread your post more carefully.

I got rid of TGPro as it didn't seem to help. The tech person at Apple Support is blaming the video card. I have an appointment at Apple store on 4/27; I'll let you know what they say.

Hi Michael, i've been following this thread for many months since i've been dealing with the same issues for as long.
I'm replying to you because i've been tempted to do the same: take my machine in to have the video card checked out.

I use Mid-2011 27" iMac for a second display and it suffers from the blackout screen thing. Since i use it as my second monitor, its not 'critical' per se - but it severely hinders my workflow. ... a few months back the HD started making a clicking sound, so i took it in to the genius bar to diagnose and my hard drive had failed. ...and even though i brought up the screen issues, his diagnostic test didn't show anything.

So now after investing in a new hard-drive i've found myself doubled-down on this machine. Though i'm tempted to bail on it, and just buy a different used one (i'm on a budget & its only used for a second display) if the cost to replace the video card is above $600.

Please do follow up on this thread after your appointment and let us know what transcends. Good Luck, and Thanks!

Hi Folks

I've reported on this same issue back in the fall of 2016 on my 2011 27" and also assumed it was software related as it was intermittent and a reboot or zapping the pram quite often solved the problem. When that failed to work an initial visit to an Apple repair depot oddly showed no apparent problems on the bench...of coarse : ( ... but the issue continued shortly after and was alleviated by having the brightness set to full.

It has been fine since December but recently the screen did not come on at all and the Imac gave one chime at start-up and shut down.

Thought it may be the power supply but all indicator lights showed it was fine and disconnecting the display the Imac booted without problem so a return to the Apple service center had them swap out from a working Imac, the display (mine was replaced under warranty in 2013) and the video card ... problem persisted, the tech finally did an exchange of the backlight which solved the problem so a new one was ordered in and my Imac has been working trouble free without any issues for the last few weeks, Cost was $180 Canadian plus install.

Hope this helps but may not not be the solution for all.

I've been having this issue for well over a year now and have tried just about everything anyone has suggested, except for spending money on hardware (I just can't justify throwing good money after bad).

The Ctrl-Shift-Eject [pause-2-secs] Shift-Key wakeup method always works for me.

I had a bout of about 10 blanks in a row just before starting this reply - soo frustrating! I turned off the auto-brightness adjustment, which seemed to work... but alas - it just blanked again while I'm typing this.

I noticed that my keyboard brightness controls also stopped working there for a few minutes (volume controls still worked fine). It's sorted itself out now. I'm not sure what that was about - it could be related? Who knows...

Could this just be an OS bug? One which crept into the OS a few years ago and is only prominent on non-latest-gen hardware? Would this still happen if we were running the OS version that originally came with the machine? I rebuilt the machine from scratch last xmas, to no avail, but I reinstalled the current macOS at the time...

I have a 27" iMac (mid 2011). Can't remember what OS version it came with at the time. Is anyone still running the original OS on their 6 year old iMac, though? If I put on my cynical hat I'd say this issue is known to Apple and they have 2 options. Option 1, spend debugging/development resources on finding this *nasty* bug in macOS (and probably earlier versions) to make our ageing iMacs perfect again OR - Option 2, get us to buy the new iMac (when the old one is still perfectly up to the task).

PS: Take note Apple - this has been a 31-screen-blank reply for me - Oops, make that 32 :-)

Hi croozey,

My 27" is a mid 2010 if that's any help and came with Snow Leopard. Not sure how long it was before I upgraded to the next OS, but I do know it's only been since the last 2 upgrades I've had the issue. Yosemite seemed fine but my blank-outs began well into El Capitan, so I'm inclined to think it was an update applied to El Capitan.

Thank you SO MUCH for the Ctrl-Shift-Eject [pause-2-secs] tip. Man, my biggest frustration has been waiting for the "sleep" to kick in so I could wake it up again. There's only so much stuff you can do on a smart phone.

I called an authorised Apple Service Centre here in New Zealand and he reckoned it was either a Graphic Adaptor issue or more likely an LCD screen issue. Biggest problem with that, he said, is there aren't parts around any more and I'd be unlikely to find a screen. My only remaining option? Replacement! Not entirely convinced about that but it will depend how much the frustration levels escalate.

I struggled for ages trying to work out how to avoid this nightmare. After I got blacked out playing on a final table in a poker tournament which cost me the equivalent of £1000 I decided to buy and connect to the iMac a cheap monitor for about £50 and put my £1800 iMac dream machine under the table where it languished contently serving out the remainder of its life. I virtually gave it away as I was so disgusted with it. I will never ever buy an iMac again

I have the whole suite: iMac, iPhone, iPad, MacBook Pro & Apple Watch and I do love how well they all work together.

I just cannot bear the thought of contributing this ageing but still near-perfect iMac to land-fill on the back of just this issue, especially since it could turn out to be a software-only issue. But it has now persisted for well over 12 months and it is slowly sapping my trust in Apple's ability or willingness to deliver products that last longer, in favour of the next sale.

We pay a premium for quality products which are expected to last longer. In this throw-away society, if I cannot expect more than just the warranty years, why continue to pay a premium?