iMac 2011 screen goes to sleep randomly

quick solution for black screen (for us at least)

iMac 27 2.93 i7, 16GB ram. Screen goes black randomly after Lion upgrade 10.7.3.

This issue just started for us about a week ago, and i finally found a quick solution to avoid a restart after a blackout.

When it goes black the CPU and system is still running, but can't do anything without force restart. Mirrored monitor stays on and i can work, but its a pain. The blackout is intermittent and i can't recreate the issue. Have restarted, Reset PRAM, SMC, prefs, privledges...everything.

This worked for me to get the screen to come back on without restart:

Shift+Control+Eject key. This forces the system to switch back to the inegrated graphics and not the nvidia drivers, which is causing the blackout.

http://reviews.cnet.com/8301-13727_7-20083947-263/some-lion-users-plagued-by-black-screen-bug/

Edit: Ironically while i was dropping in the link above, the monitor went black again and the little key fix got it back. Hope this is addresses soon by apple, it's got to be a hardware issue!

Gigabitten said:

iMac 27 2.93 i7, 16GB ram. Screen goes black randomly after Lion upgrade 10.7.3.

This issue just started for us about a week ago, and i finally found a quick solution to avoid a restart after a blackout.

When it goes black the CPU and system is still running, but can't do anything without force restart. Mirrored monitor stays on and i can work, but its a pain. The blackout is intermittent and i can't recreate the issue. Have restarted, Reset PRAM, SMC, prefs, privledges...everything.

This worked for me to get the screen to come back on without restart:

Shift+Control+Eject key. This forces the system to switch back to the inegrated graphics and not the nvidia drivers, which is causing the blackout.

http://reviews.cnet.com/8301-13727_7-20083947-263/some-lion-users-plagued-by-black-screen-bug/

Edit: Ironically while i was dropping in the link above, the monitor went black again and the little key fix got it back. Hope this is addresses soon by apple, it's got to be a hardware issue!

Click to expand...

Mine did the same thing 6-7 months after I bought it in May 2011.
They changed the graphic card, it still does it from time to time (a lot less than before).
The only workaround I found it to minimize (not eliminate the problem) is :
1- turn the brightness to the minimum
2- turn it off every night before going to bed
Some people claim that replacing the LCD fixed the problem.

FYI, the ctrl, shift eject, I beleive forces it to sleep and then moving the move will wake it up. This is what the kernel logs appear to say. It will also drop a vpn connection as the netwrok resets...

Gigabitten said:

This worked for me to get the screen to come back on without restart:

Shift+Control+Eject key. This forces the system to switch back to the inegrated graphics and not the nvidia drivers, which is causing the blackout.

http://reviews.cnet.com/8301-13727_7-20083947-263/some-lion-users-plagued-by-black-screen-bug/

Edit: Ironically while i was dropping in the link above, the monitor went black again and the little key fix got it back. Hope this is addresses soon by apple, it's got to be a hardware issue!

Click to expand...

Thank you so much for this great tip.

Mine has just started doing this and I have been turning it off each time. Incidentally it seemed to start doing it soon after I enabled a hot corner for a black screen. I turned it off as I kept going into the corner by mistake.

It usually happens shortly after my screen has gone off as per Energy Saver defaults (computer and screen sleep 10 minutes, but screen dims before shutting off), but last night it just shut off whilst I was browsing.

Just started for me too.

iMac 2011, OSX Mountain Lion 10.8.2
3.4GHz Intel Core i7, 16GB 13333Mhz DDR3
Startup drive: 250GB Flash SSD
Other drive: 2TB SATA

First thing I noticed was random screen brightness changes this past week - I've just moved the computer so I initially thought that the room's lightbulb was a bit rubbish and was playing merry hell with my brightness sensor.

Then, today, for no reason (just like everyone else's) the screen went black. I thought we had had (another) power cut, but everything else was fine. I realised that the HDD was still spinning so I thought I might have accidentally put it to sleep or the screen had gone onto power save. When I wiggled the mouse or pressed the keyboard, nothing happened, so I tried the on/off button (a quick press). This caused the HDD to stop and put the computer to sleep.

Pressing the on/off again caused it to wake - I was halfway through a document and nothing had changed. The same has happened twice since then today, with no real reason why. I haven't changed any settings, haven't installed any updates or new applications. I turn the computer off every night (but often use Resume), only have one account and haven't done anything recently to put it under any stress.

In retrospect, I do think I saw a wobble a moment before it had its little episode.

sams89 said:

iMac 2011, OSX Mountain Lion 10.8.2
3.4GHz Intel Core i7, 16GB 13333Mhz DDR3
Startup drive: 250GB Flash SSD
Other drive: 2TB SATA

First thing I noticed was random screen brightness changes this past week - I've just moved the computer so I initially thought that the room's lightbulb was a bit rubbish and was playing merry hell with my brightness sensor.

Then, today, for no reason (just like everyone else's) the screen went black. I thought we had had (another) power cut, but everything else was fine. I realised that the HDD was still spinning so I thought I might have accidentally put it to sleep or the screen had gone onto power save. When I wiggled the mouse or pressed the keyboard, nothing happened, so I tried the on/off button (a quick press). This caused the HDD to stop and put the computer to sleep.

Pressing the on/off again caused it to wake - I was halfway through a document and nothing had changed. The same has happened twice since then today, with no real reason why. I haven't changed any settings, haven't installed any updates or new applications. I turn the computer off every night (but often use Resume), only have one account and haven't done anything recently to put it under any stress.

In retrospect, I do think I saw a wobble a moment before it had its little episode.

Click to expand...

Take it into the Apple Store and they will sort it. It's a well documented issue that they know about and will involve replacing the LED backlight and fitting a new LCD, it comes together as a service kit.

Luckily I still had a month of the original warranty left so it didn't cost anything, but my receipt showed that it would have cost just under £400 if I had to pay for it. I purchased the additional Applecare warranty quickly before my 1 year one was up.

Good luck.

this started with mine out of the blue a few months ago.

It's driving me nuts.

Possible Solution to sudden sleep...

I may have a solution but it may not be the answer. question is, have you ever placed anything magnetic on the left side(the area next to your trackpad) of your macbook? I had the same problem and i finally figured out why it was happening. the detection for anything magnetic triggers it to go to sleep. so it would help by not placing anything magnetic onto that area. hope this helps!
other than that, if this doesn't help, sorry

I set up the bottom right corner as "put monitor to sleep" so when the screen goes black a quick trip to the bottom right and out again brings it back.

Imac goes to sleep

I found the vent was completely caked with dust. As soon as I cleaned it out, this problem stopped. Seems like it's a protection against overheating.

This is the iMacs heat protection system kicking in to protect it. Three things cause this: improper air flow, bad heat sensor on power supply, overheating power supply. Try cleaning fans, if that doesn't work likely a new PS is needed. I saw this exact issue a few months ago, turned out the PS was damaged from overheating due to clogged ventilation. Cleaned it and replaced the PS fixed it.