iMac screen goes black, but system runs fine in background

Another thread for the same problem:

iMac 27" Black Screen?

Did you put your mac on another laptop while using it?

If yes, then don't. My mac went blank because of that.

I have had all of the problems stated above: screen backlight would not stay on past half brightness level. I've had to keep my screen on the lowest brightness setting in order to have a functioning computer. It would almost instantly cut the backlight and i would have to prompt it to wake up from sleep (control+shift+eject).

After changing the backlight board it did not cure the problem.

Although i have just removed the vsync cable from the display to the backlight board and everything is now fully functioning. My brightness has been on maximum and I have had no problems since. Although I've yet to replace the vsync cable. I did see some of the contact points were damaged.

Yeah thanks, it does sound like my problem but I have the 2.7GHz with AMD Radeon HD 6770M 512 MB and they don't acknowledge a problem with that model.

Thanks a lot for sharing your experience with the vsync cable. Did you removed the sync cable and it works or did you replace the sync cable and then it works?

I turn the vsync "off" (graphic tools for xcode -> Quartz debug-> Show Beam Sync Tools-> disable Beam synchronization (it´s not a permanent adjustment)) but if I set a higher brightness the screen immediately turn black.

Which Imac model do you have?

This happened to me (Currently using an imac late 2013, bought in feb) maybe a coincidence, but seemed to start when I updated to 10.10?

Kept doing the alt+shift+eject and it worked a few times. Annoying fix, none-the-less. After doing that for a few days, I suddenly got a black screen. Shined a torch on it and could see my desktop - so that was a massive worry.

Shut my computer down and did a PRAM reboot. I then verified my disk etc. and it hasn't happened since (That was 24 hours ago. Since then I've managed to watch about 3 films and surf the web in between.)

I have also switched back to an old keyboard as I see that is suggested here.

Hope that helps!

Late 2009 27 inch Imac, quad 2.8 I7 processors. This black screen crap started about a week ago which happened occasionally. Thought it was a heat issue so I unplugged cable and just turned computer back on when cold to the touch. 1 minute later, black screen.

I finally figured out the problem. Apple ***** ***. They should have a major recall of every Imac just like automobile industry does. It sickens me to know that people are paying up to $900 to have this fixed. I am going into Apple store tomorrow and telling the store manager politely, that if they do not fix my computer for free because this is a know issue, I am going to yell at the top of my lungs the following

"attention customers looking to purchase an Imac. Please do not do so until you go home and google "Imac and black screen problem" The manager will panick because it's 3 weeks before Christmas. I will go to store everyday until they fix a known defect for free. How ****** up can a company be when they have known for years about this issue and no recall. I am going to contact Channel 4 news and channel 7 news here in NY and they will be all over this because it's documented all over the internet. People work way too hard to purchase a $2,000 computer to deal with this crap. The thing that really ***** *** is that once you use an Apple, you can never go back to a Windows machine.

Go into your local apple store on a busy weekend and tell people looking at Imacs to forget buying one until Apple fixes this issue. Take out Iphone and google the issue and show customer all the threads that come up. Than tell the manager that you cost them 2 sales today and you will be back on the weekends until you computer is fixed for free. If that doesn't work, I will take them to small claims court and will provide the judge with the 1000s of posts that are online and even on youtube about this known bug. If you are uncomfortable speaking up for your rights in front of 100 customers in the store, bring 100 small pieces of paper and write down the following "do not even think about buying an Imac until you go home and google "Imac screens going black"

The amount of time and loss productivity from all of us going to the forums to find answer is ******** when Apple knows they need to recall tens of thousands of Imacs. It's all about the stock price and keeping investors happy. They should be more concerned about keeping consumers happy.

Sorry for flipping out with this post, but I can't allow Apple to get away with this crap any longer.

I will let everyone know what happens after I go to Apple store this Wednesday Dec 10th.

Cheers

BobbyD

Just a quick update,i have been using my 2010 Imac running Mavericks for 4 months on 3 brightness and it hasn't gone off once.

Even though this is not acceptable i have spent previous days,weeks and months constantly fighting against the dreaded black screen courtesy of Apple.

I decided yesterday to upgrade to Yosemite,my system will run it fine and i have a Iphone that i can use with Yosemite.Installed from a USB drive and began using Yosemite after 2 minutes i received the dreaded black screen,got the screen back on working via Ctrl alt eject reset and within seconds it was off again.

Tried resetting the system as advised by Apple,after 30 minutes i once again had had enough of this problem,i wiped the drive and time machined back to Mavericks.

System back to normal now(well as normal as can be)No black screens😕

Any updates Bobby?

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 had not gone dark on me. I should note that even at this temperature, if I block the central part of the vent slot, the computer will go dark within a few seconds. So, as long as I don't do this, I can now use my computer without the dreaded black screen.

Well this is strange, and may be good. I was minutes away from going to shell out $500 to get the LED display on my late 2009 27 iMac replaced, and I decided to give it one last try.

I hooked up the 27 as an external monitor to my 24 iMac via the mini displayport cable.

After being black for 4 months, the darn 27 monitor works! It works as an external display. Which means the monitor is probably not defective.

What does this mean? Thanks.

Thank you.

I tried every fix suggested. Ready to throw out my very expensive but now unusable imac I had one last go - I replaced the keyboard.

Bingo!

Everything is back to normal. Such a simple solution. I urge anyone with this problem to try it.

I replaced my keyboard and it (temporarily) solved the problem for the Black Screen issue on my 2009 iMac. After a short period of time, the black screen problem returned.

I've had this issue for about two months, and like for many here, nothing worked. I was about to buy a new computer, when a friend sent me SMC RESET INSTRUCTIONS THAT WERE DIFFERENT, AND IT WORKED! All the instructions I'd seen before didn't mention you need to remove all peripherals, and holding down the power button after you've done so. This probably won't work for all, but I had to post in case it works for some. Here's the complete instructions:

SMC reset

1. Shut down the computer
2. Unplug the computer’s power cord and all peripherals (anything in the USB port etc. EVERYTHING)
3. Press and hold the power button for 5 seconds
4. Release the power button
5. Attach the computer’s power cable
6. Press the power button to turn on the computer

Then,

PRAM Reset

1. Shut down the computer
2. Locate the following keys: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4
3. Turn on the computer
4. Press and hold the Command - Option - P - R keys. You must press this key combination before the gray screen appears
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time
6. Release the keys

I hope this works for some of you as it did for me!

A sad update to this. This worked for an entire evening. Put the thing to sleep. When I got up this morning it went back to its old self. Tried the resets again, and it didn't work.

The one thing I'm hung up on is that when I did the PRAM Rest (when it did work) I never got to the second startup sound. No idea what that means.