iMac screen goes black, but system runs fine in background

Experienced this "black" screen problem on my late 2009 iMac. It started a couple of months before it was booked in to have an SSD drive fitted. It happen twice a day initially, but by the time it was taken away to have the new hard drive fitted it was every ten minutes or so. During the SSD install it also had its logic board replaced due to faulty connector and upon return the machine is so much faster, but the black screen problem is still there. Done the PRAM resets and the other one and turned down the screen brightness ( which helps prolong the cut out time but still not a permanent solution). Tried fan speed software, but no better.

Decided this morning to look at energy saver settings and discovered they were set at 5 mins for display and computer sleep. I increased them to 1 hour, ignoring the warning about being more costly to run and also wearing out the display and drive sooner as I wanted the thing to work!!! and voila the black screen has vanished. I've even turned the brightness back up to full which previously seems to crash the screen to black and no problem.

So don't spend money on software, or hardware try this simple adjustment of your "sleep" settings in System Preferences - Energy Saver first and see if it that resolves it for you. I assume an IOS software update must have altered these settings at some point as Ive never been into Energy Saver before

Interesting to read your story gohunter, I will save that for later in case my blackouts come back but here's my very different story which also seems to have fixed my iMac. I have been suffering with screen blackouts for years now—I think there’s some confusion between the 2009 backlight failure and the mid 2011 blackout problem. For the record, mine is the 27” mid 2011 with HD 6770M video card and Mavericks. I have had long periods (months) without blacking out, usually with the brightness set to 3 blocks but recently it became unstable again and I was constantly having to use Ctl-Shift-Eject to see what I was doing. (My iPhone is always on the desk with Bluetooth on)

So my latest fix came about when I was to trying to get the Fan running faster with SSD-Fan-Control - thinking this was an overheating issue. This was giving me some success and I was running with the screen much brighter for longer periods but it didn’t last. Interestingly the iMac was running pretty warm at the back even with the fans blowing hard and getting quite noisy. I then accidentally launched SMC Fan Control - I forgot it was even installed and it’s not likely to be a good idea to have both these fan control apps working on the same machine. So I set SSD Fan Control back to Auto and hit the Reset button in SMC Fan Control to return to defaults. That required a reboot and I did PRAM reset for good measure at the same time and now my iMac is perfect. Running much cooler, no fan noise, and no blackouts with the brightness midway. One other thing I did was to tick auto brightness in the Display Settings. So out of all this, I don’t know what actually made the difference but I am very happy with how things turned out. Hope it helps someone.

My mid 2011 iMac hasn't so much as blinked since I did the fix in my previous comment. research this fault and the fix for that will cure your black screen too: (Apple iMac 27" Dark Side Screen Failure - The Manufacturing Fault Apple Will NOT Admit!! - YouTube )

My previous diagnosis may have been correct, it certainly worked much better for a few weeks but then for the first time I started having the well known issue where the left side of the screen goes dark. I followed the fix on YouTube: (Apple iMac 27" Dark Side Screen Failure - The Manufacturing Fault Apple Will NOT Admit!! - YouTube ) -this involves digging out the plug at the back of the LCD screen and soldering the wires directly to the board. Not easy to do, I can tell you. But now several weeks later I'm very happy, and the iMac has been good as new.

This is very frustrating and so many people seem to have the problem. I'm a 2010 27" iMac user. I am a little surprised that Apple didn't issue a product recall. It also makes me nervous about ordering parts on eBay because how far along are they from failure, too?

At the moment, I have El Capitan installed, having firstly gone back to Snow Leopard just to see if the problem exists there, too, which for me it does. I have tried so many of the suggested quick fix solutions but none have worked, sadly, though I greatly appreciate all of the suggestions given.

Clearing the PRAM briefly seemed to work but only for a minute or so. The only way I can get the iMac screen not to go completely black is to have the brightness set to its lowest point. If it's a very cold day, I can have it around 20% higher than that but not for long.

This model has had so many problems, for me, including the noisy Seagate hard drive. I am going to strip down the iMac and replace the thermal paste on the CPU and graphics card, which I should have done long ago, the temperatures were a little higher than other users and, in my opinion, when under load for long periods, are really too high for long term stability of the iMac. I resorted to using the iMac as a screen for a computer but it still got very hot. Like a lot of people with the 2010 27" model I have cloudy areas on the screen from dust that requires very carful surgery (ribbon cables) and aluminium tape (does anyone know what tape Apple/LG use) to remove that dust.

I hope the next generation of domestic iMacs feature the same cooling system that the iMac Pros use and that there is some concession made to people who want to upgrade memory and storage. It's unlikely that my replacing thermal paste and re-seating cables will make a difference (to the blackouts) but I will report back, either way. The iMac is long enough out of warranty that it seems worth a go.

Update on my previous post Having concluded that this is not a hardware problem I too installed the TG pro software and set the fan to 10%. I also went into system Preferences and turned off energy saver also turned off screen saver. My screen is set at 100% brightness and I haven't changed it what I did do is go into accessibility and changed the settings there as displayed below. Now this hasn't fixed it completely but it is far more stables ie I'm getting around 6 hrs usage before it goes black to bring it back up again I just fiddle with the display settings and then reset to what's shown below. Not the ideal solution I know but at least I can get my work done ( Thank goodness for the second screen) I have noticed a few other odd things with this problem such as I don't always get asked for my password when I log in it just goes straight to my desktop. setting the Mac not to change the background image is ignored the image still changes. I lost all the extra desktops I setup. although I have upgraded to the latest OS I'm seriously considering wiping the drive and doing a completely fresh install. The main problem with such a drastic measure is the time it will take.

I was having this same problem as well and so the computer has been standing unused for a couple of months until i could afford to fix it - in the meantime i have got a new iPhone so I went to switch on the iMac so that I could quickly back up my old phone before the screen gave out, then I could plug in my new phone the next time and the back ups would just run in the background even after the screen went off was the theory. However when I went to switch it on it was making the startup noise but nothing was happening on the screen at all and then the computer was just switching itself off and not even trying to boot up..??!!! HELP!!!!

Thank you to everyone who shared their story. I have been reading through the posts here and on the web, watching videos on YT the last few nights trying to ascertain the correct fix for the blackout screen problem on my, late 2009 Imac 27” 2.66 GHz i5 16GB Ram ATI Radeon HD 4850 512MB. I sincerely appreciate all of your notes and experimentation. This is my fourth Apple computer in 21 years, the last was a short-lived G5, and I hope they will eventually come clean and address the issue.

Don't know if it makes much difference at all but the Fan Controller I use is called HDD Fan Control.

I've messed about with various settings to increase speed etc but this made no difference which convinced me that it was not a cooling issue. Also, by "increasing" screen brightness to 100% alleviated the problem (for a while). These things together seemed to defy any suggestion that it was a cooling issue. Since my OS upgrade on the 12th April I haven't encountered a single black out. Long may this continue. Just to follow suit I've attached a screen shot of the HDD Fan setup.

Send Apple feedback. They won't answer, but at least will know there is a problem or a suggestion for change. If enough people send feedback, it may get the problem/suggested change solved sooner.

Feedback

I recently ran into the same problem with my iMac (27-inch, Mid 2010) 2.8 GHz Intel Core i5 ATI Radeon HD 5750 1024 MB computer w/ 16 GB of ram. The screen started flickering than blacking out all together shortly after updating from El Capitan to Sierra. I called Apple and the technician basically told me there was no know issues with upgrading to Sierra. I tried Resetting Vram, Pram, using a different keyboard, booting in safe mode, etc. Nothing worked.

In the end resetting the computer back to El Capitan was the solution. No issues experienced since reverting using "Command-R" during start-up. Instructions available by following the link here: How to reinstall macOS - Apple Support

They do not offer hardware support for this iMac any longer, so I was glad to get back to having a monitor that functioned normally. A couple of years ago I had the power supply replaced, but have had few other issues with it since. Best of luck to those experiencing the same issue.

I don’t know why but that seems to work!! Had the same problem with my late 2011 iMac ; thanks

wildkarde, i am running el capitan and have the problem.

Hi,

I tend to agree with sureguru, but sadly after being in an apple center for 2 times with no success (they didn't had the issue) and after trying all the possible solution posted here and on other forums, I ended buying an external monitor (Dell UltraSharp U2312HM).

This just to let you know it's a viable solution, not the best, but viable.

So, i've been dealing with this issue for awhile with an older (2011) 27" iMac that i use as a second monito

A couple of weeks ago i finally scheduled an appointment at the Genius Bar. .. It turns out its a video card issue.

I think i paid $150-ish and it was ready in a few hours. Problem fixed.