imac 27 black screen

I was plagued by the same situation about 6 months back and stumbled on something that worked for me. I am not sure if this fix will work for your problems but by putting the iMac 27" to sleep using the apple menu and selecting "sleep" and then waking it, the video issue has not reoccurred. Saved me a trip to get it repaired. Since then no video or black out problems but I do hear the occasionally ark and spark like the old cathode tube monitors. Try this, it's simple and free...

I'd take it back, if the computer is still "awake" when the screen goes black then it could be the same problem I was having. Either the Backlight board or the LCD or both. If your computer is under warrenty they should fix it no problem. As far as putting the computer to sleep and waking it, that didn't make any difference for me as it was a hardware issue not software for me.

Thanks for the tip, I had tried this as well as the SMC reset. This along with being unplugged for a few days seems to be the most reliable way of getting it to work fine for a day.

Actually I leaning towards some environmental factors. I did several things that did not help :

- use a circuit that is on a different home 20Amp breaker

- unplug Linksys wireless router and connect direct to DSL model.

The last option I am testing right now is to move the iMAC away for the DSL model.

I had it sit on the washing machine during the day yesterday, no problem (and cancelled my Genius appt), then at night moved it back to the desk, black screens again.

Today I am sitting on the floor in the living room, so far so good.

I will report in a few days with my findings in case it helps other folks.

I got mine back a few days ago. So far it's working just fine. Keeping my fingers crossed that the problem is permanently solved.

The report said they changed the LCD display and the LED backlight board and it had passed every other software + hardware test. So I'm quite hopeful it stays that way.

Hi Eve - How did you get on with this? I have exactly the same issue - as do many many with iMacs.

Since I got the iMac back everything has been normal and working fine. No problems anymore.

Apparentyl it was a hardware issue and you can only change the display.

Hi, I hope you find this information useful:

A few years ago, we purchased iMac 27" 11,3 (Mid-2010) (with i7 2.93Ghz, ATI 5750 1GB VidRam, etc.) for our offices and software development team. They were originally shipped with Snow Leopard and worked as expected and without any problems. However, a year later, we upgraded to Lion and all of machines immediately exhibited the same problem: the screen would go to sleep by itself and would require a hard reboot or sleep on/off. (Only the screen was asleep and the rest of the iMac continued to function; this was confirmed by screen sharing to the machine.)

Due to the severity and impact on our business, we immediately contacted Apple and their genius bar staff in New York/SoHo. They were unable to determine the root cause, so they replaced all of the logic boards, video cards, and screens, and got us back online asap. This resolved the problem, but we were curious to know why. After days of rigorous testing, we concluded that the issue is caused by a bug in MacOS. Specifically, faulty Kext files (Kernel Extension files extend the functionality of the MacOS Kernel) for the ATI drivers. So, why did the replacing the hardware work? We think that the Kext files that were released and distributed with Lion (and later MacOS versions) correctly supported the newer hardware revision of the replacement components, but not the older ones.

If you're experiencing this problem, short of replacing the components or waiting (for another 3+ years) for Apple to hopefully fix their OS software, you can lessen the effects and be able to recover faster by doing the following: (Please bear in mind that these are not permanent fixes.)

1. Turn on "Hot Corners" and assign one corner to "Put Display To Sleep". When your screen goes to sleep, move your mouse (which still works) to that assigned screen corner for a second, then move it again. This will wake your screen. You may have to do this a couple of times, but it's much faster than a hard reboot or a sleep on/off for your iMac.
2. Turn the brightness of your screen to a low setting (10%-15% of the total brightness).
3. Turn on screen sharing, so you have a last resort method of accessing the machine.

If you're not convinced that it's a MacOS software problem, then do what we did and see for yourself; install Windows 7, Windows 8, or Linux via Bootcamp or as the only OS on the iMac. Those operating systems and drivers worked flawlessly for us; the bug does not occur and the screen does not go to sleep, but if you dual boot and switch back to MacOS, the bug reappears because the iMac is loading faulty Apple MacOS software.

Good luck!

Since these threads aren't merged, I'm posting the same in several threads.

I've had the screen blank problem, took the IMac in twice, got home, still not fixed.

But they used their own keyboard in the shop and couldn't reproduce the problem. I switched keyboards and so far so good. It's been 3 days now.

I'll keep folks updated. Don't get a new graphics card before you try a new keyboard.

Be sure to take the batteries out of your keyboard when testing another one as the board does not turn off if it is like mine.

SOLUTION: Cleaned dust off fans!

Background- I had this problem for at least 6+ months. I tried all the software fixes, reformatting, fan configuring, adjusting brightness, sleep, no sleep, delete software, reinstall, folks I TRIED EVERYTHING, even all the suggestions from an Applecare support guy with no avail!

I took it into an Apple repair shop and after 2 days the tech was unable to duplicate the problem. He mentioned that the screen, video card, logic board, and the various hardware solutions were going to be about $600-$700 each! I took my iMac 27 home and looked through the discussions once more, just in case.

A few people posted that dust build up on the fans caused their black screen. I looked up how to clean the inside of the iMac on youtube. Went to the hardware store and bought a suction cup grab handle for a bathtub, pulled off the screen and sure as ****, the fans and heat shields had a good amount of dust. I used a small vacuum and canned air to clean them off. I carefully put it back together and guess what.... NO MORE BLACK SCREEN!

Try this as a last attempt before spending hundreds on a repair. If you can't do it, have the tech try this option first.
Good luck!

After the new keyboard fixed it for several weeks and I read about the LCD cable, and the fact the thing worked both times I took it in and lasted a couple weeks, I went with 'jostling it'. It's been OK for a week now.

pbook4g5:

"...the ribbon cable between the display and the LED driver board. As I stated in my repair notes a few pages back (and now a few months ago), the only thing I could do to fix the issue was to install a new display, which had a new display cable attached to it."

That's the one fix that makes sense.

I don't see how dust on the fan makes any sense. Software makes no sense.

Definitley I'm not going to start replacing expensive parts. I'm going to keep trying the jostle and the simple things. And when it finally breaks for good, it should be testable.

It's still as annoying as heck. Solutions are beginning to border on superstitions. You try something, it works. Then the problem comes back weeks later and it turns out the fix was coincidental not the cause.

I do hope cleaning the dust on your fan works for you.

Happening to me too. One year old 27 inch iMac. I have native Windows installed and it happens there too so for me its a hardware issue, not related to OS X. When it starts to happen I've tried to unplug my keyboard but that doesn't help. I suspect it's related to USB because when I used Wifi keyboard it didn't happen. Assigning a hot corne helps and also the trick by putting computer to sleep and back from Apple menu also seems to help temporarily for a few hours. Weird.