iMac 27" Black Screen?

I noticed that after display went black, my external speakers also reduce the intensity and loudness. So, I have to hit ctr+alt+ eject and then turn the volume up.

Hi Guys,i too have had the same problem for nearly 2 years with my mid 2010 Imac.

When this first started i did the same as everyone else,googled it hour after hour with no working results,i have my xbox 360 connected to my Imac via display-port-HDMI video converter,i also get Black screen when my console that is up and running,once again that can work for weeks and then black screen appears

i can sometimes run my Mac for weeks and weeks and then it just starts,i have taken the Mac apart and cleaned it of dust,several times now,tried All the OSX'S from S/L including Yosemite.

I usually have to have my brightness set to 4 marks,any higher and it black screens,it black screened a few weeks ago and out of total frustration once i got the screen back on i turned the brightness up 1 dash over half and the screen stayed on!!!

It worked for several weeks and has decided to play up yesterday,messed around for 3 hours this afternoon watching it black screen and also losing signal for my xbox360,tried several different Brightness settings to no avail.As i type this it has stayed on for 20 minutes now on Brightness mark 3,which is way too dark for me.

Over the past 2 years i have tried everything,i can use my Mac no problem for weeks and that includes my Xbox 360,then all of a sudden it black screens and the nightmare starts again.I know the problem is not with my Games console as it works on other screens including another 27" Mac.

I have emailed apple and basically been told to take it Genius bar which is 2 hours away from me,i bought my mac second hand so have no warranty

I have a friend who has the exact same problem with the black screen on his 2012 Imac,i agree its deffo an engineering issue

really sick of this problem on a £1000 computer

Steve

use option+command+ eject then click your mouse. this usually helps but i'm at the point where it takes more than 5 tries to keep it on that i restart the computer. I've been having this problem for months now others have speculated its a million things but nothing helps. it goes away for awhile or happens less even gets to the point where the before mentioned sleep shortcut works on the first try but personally its gotten worse as of late. My guess its an apple error in the making of the imacs because all gens have it.

Has anyone got a link to the keyboard post???can't find it,thanks

I noticed that after display went black, my external speakers also reduce the intensity and loudness. So, I have to hit ctr+alt+ eject and then turn the volume up. Anyway, it's been a quite a while that this issue hasn't happened again (black screen). I am running fans in default mode via iStat menus. Fingers crossed.

My 27" iMac got to the stage where the screen was permanently black except for a few seconds on startup and when waking from sleep, though the computer worked fine and I managed to limp along by setting my second monitor as the main monitor. It was bugging me as that was far from ideal. Then I came across this post and tried switching the bluetooth keyboard off - so far the iMac screen is working perfectly again. I happened to have a very old (and very long) apple usb kb hanging around, so I'm using that with no problems so far. I've been maintaining my own macs pretty competently since 1995 but I'd never have guessed this one without reading here, so thanks very much! 🙂

I found a fix.

I am running Yosemite and my iMac started to have this problem after I tried a bluetooth keyboard. It still had the problem even after I switched to a USB keyboard. Now after I turned off all three options in the Blue tooth advanced menu, it never goes blank screen again. These options are:

[] Open Bluetooth Setup Assistant at startup if no keyboard is detected

[] Open Bluetooth Setup Assistant at startup if no mouse of trackpad is detected

[] Allow Bluetooth devices to wake this computer

I thought the wireless keyboard fixed the issue and it did for the longest time, but that was only about a week. I just tried your suggestion and that isn't working for me either. I even switched the iMac's bluetooth off completely, using a usb mouse and kb, still black screened. That suggests to me it's not a bluetooth problem.

So far (on mid 2010 iMac with 12GB RAM) I have tried:

Switching all bluetooth off.

Unplugging all external devices including my 2nd monitor, a dell 24" and running the mac on its own - even without internet connection.

Resetting PRAM and SMC.

Verifying and repairing permissions.

verifying HD, no faults found, it is a relatively new one as part of the replacement program.

Scanning for baddies with ClamXav.

Checking for any firmware updates.

The problem began under Mavericks and has persisted in exactly the same way on upgrading to Yosemite, suggesting either a hardware problem or a software bug that hasn't been squished.

One constant is that my 2nd monitor, 24" dell which is much older than the iMac never blacks out, thankfully. At least I can still work, albeit in a more cramped and degraded way.

A 4 year old computer should still have years of life, especially when you pay a premium.

This is fun! 🙂

In 20 years as a mac user I've never had one give up, that's why I've always been a rock solid mac user. Perhaps times and standards are changing - or perhaps statistically speaking, it was simply bound to happen at some point!

Grateful for the continued suggestions though.

This is what i tried on my 2010 intel i5 imac

remove dust (one day good)

unplug and plug all the cables from the monitor including the small backlight cables in the corner (one day good)

set the sleep-mode to "never" (no effect)

set the brightness to 4 blocks (seems to occur less)

set the brightness to 6 blocks (seems to occur more)

PRAM reset (no effect)

SMC reset (longer problem-free intervals after reset)

set the brightness to 80 % yesterday (didn't occur since)

turn off the bluetooth an hour ago (didn't occur since)

i have a wired keyboard and mouse.

it occurred in cold and hot conditions.

it occurred several times while browsing and playing minecraft.

it didn't occur once in screensaver mode.

When it happens it happens several times in a short time.

it occurred once in mavericks the day before i upgraded to yosemite.

After the upgrade to yosemite it went a lot worse.

it occurred while running ubuntu from a USB stick.

I hope this helps, if everyone analyse the conditions in with it happens maybe we could one day find a real cause.

It drives me mad,

Thanks Manuarmata. That's interesting, the one thing I hadn't tried was setting the brightness slider. On opening the monitor panel it was set to about half way despite the monitor always looking as though it was on full brightness, so I set the slider to full brightness and for the first time today I'm able to use the primary monitor. This could of course be pure coincidence, but I'll post as an when anything different happens.

Cheers

I have a late 2009 iMac 27 inch.

If I raise the brightness above 1/3 it goes black. Hitting OPT, COM, Eject then any key will wake it up again.

Computer stays running, monitor goes black. I have an external monitor so I know the computer stays running.

I use a wired keyboard.

This happened before Yosemite, and with Yosemite. Now, the mac is back to pre-Yosemite.

I took it to the Apple service place and they replaced the video card. That did not solve it.

They said I need a new monitor, $800 (and here in Seoul, a new iMac 27 is $2500)

The darn monitor works but only below 1/3 brightness.

I can now confirm that the brightness keys (or slider in the display prefs) seem to be playing their part. After turning brightness up full I was able to keep the monitor on and got a full day's use without blackout. So the next time it repeatedly blacked out when trying to wake from sleep, I turned the monitor brightness down to about a quarter and it consistently stays on (although having the screen that dark is pretty useless.) As the brightness goes up a bar at a time, blackout hits at a point somewhere just before half way. Both these behaviours currently seem repeatable and reliable so it must mean something.

I do remember brightness set to zero used to fade the screen to black, but at some upgrade of the OS that behaviour changed to barely visible.

I also remember reading another thing related to the HD swap I got as part of Apple's replacement program. The article suggested that some SMC related connection may have been loosened during the hard disc replacement. I can't remember the link offhand but if anything comes of that I'll post.

Cheers

Savbox Your imac seems to play up exactly the same as mine!!!we have the same problem with the brightness,every so often on mine i can turn the brightness up to half and it stays on for days,one mark over half and it black screens.

As i type now i have it on Brightness 3,i have just increased brightness to 5 and it black screens,i now have it at 4 and it has stayed on.

This is a joke and now even more people are having the same problem,waste of time getting in touch with Apple.

That sounds very familiar Steve! I may have just stumbled on to something else. Are you turning the brightness up via your keyboard keys or via the system prefs>display>brightness slider?

I ask because the first time I turned it up full (a few posts back, Oct 24, 2014 3:34 PM ) I used the slider in system prefs. all the other times since I've been using the keyboard keys, but just now I turned it to full via the sys prefs slider and it has stayed on at full brightness. From now on when it blacks out I'll use the display prefs slider to see if this is a repeatable pattern as that might suggest a problem with the way the iMac and brightness keys communicate.

Cheers

I doubt it is a communication problem. I had blackouts in linux and other people talk about blackouts in windows. Personally i think it is a semiconductor problem. It is way to unpredictable to blame it on software or firmware. if just someone with very frequent blackouts could monitor the input and output voltages of the backlight controller we could get much wiser.

When we monitor the voltages during a blackout and one of the voltages drops we can replace it with a current from another source witch should be possible for someone with some electronic skills.

If all the voltages stay it is probably a transistor in the led board witch convert the 24 v current to a lower voltage but i doubt that as the left and right side are controlled separatly.