iMac 27" Black Screen?

That sounds logical. On another chat line, they said that the tech shop gave up looking for the problem, and just unhooked and re-hooked every connection. Problem solved.

If I Iived closer to a repair shop, I would bring the Mac over and ask them how much they would charge to unhook and rebook.

My screen works just fine, if it is below 30% brightness. Go over that and black.

I'm going to gather some coins and buy a 27 inch LG monitor.

Congrats.

Same problem, random black screen, stated in Mavericks continues in Yosemite. Had the video card replaced (re: stbodie). Black screen returned after a week. Have tried all of the solutions mentioned in this thread, with the exception of having all of the wires re-plugged in. Appears Apple is just ignoring this issue.

I'll throw in my two cents worth, untested. A friend rang me about this problem with his 27", mid 2011 iMac. Was unaware of this thread when I paid him a visit, but will be suggesting to him that if it is a software problem and something to do with controlling screen brightness, we should be trying Brightness Control, a small program which controls brightness.

See http://www.macupdate.com/app/mac/10429/brightness-control

I used it for years as a fully adjustable brightness control, not as a fix for the dark-screen problem.

An update, after trying everything I've read about this issue online, I finally solved it by installing the Owly app. Works beautifully, no black screen (hope I didn't just jinx myself) for 3 weeks.

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.

What about just pointing an 8 inch fan on the back of the computer. It seems that would have the same effect. I tried that but nothing.

Now, my screen stays on for only seconds before going black, no matter how low the dimmer settings.

I'm using an external monitor in mirror display to use my late 2009 iMac 27.

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.

Says to me: faulty internal connection somewhere.

I've had my friend's mid-2011 27" iMac for a week now, trying to pinpoint the problem. It's subject to the recall, but the local Apple tech and I agreed that until we can reliably trigger the fault, it's best not to send it for repair just yet.

Another interesting thing: when this particular machine goes black screen, it can always be fixed by Opt-Cmd-Eject which puts the machine to sleep. Now, sometimes after about 5 seconds the machine automatically comes out of sleep, all by itself, and the screen is okay. But other times, I have to Opt-Cmd-Eject a second time.

The tech couldn't explain this behaviour. What could be the explanation of a machine in sleep mode, coming out of sleep by itself?

Also, I'm thinking of starting a new thread: not how to fix the fault, but how to induce it. If the fault can be reliably induced, it can be fixed.

I have used the Opt-Cmd-Eject method and the screen comes back on,when my Mac was at its worse i would Opt-Cmd-Eject and then within a second it would black screen again.

As i explained the other day mine is now fine as long as i keep the brightness on 3 blocks,anymore and it black screens instantly.

Not forgetting i am running Mavericks which is very stable,i tried to upgrade to Yosemite last week and after a while of using it,the black screens came back big time!!!

My monitor had that exact same problem.

If brightness went above 50% it went black. Then 40%. Then 30%. Then it would come on for only seconds and go black.

Now, it works just fine as an external monitor.

2 months ago I took it to the Apple repair shop and then another place. They both checked or changed something that cost about $200 (graphics card? blah blah panel, board?) , and returned the Mac to me, but both times the black monitor returned.

But the monitor DOES WORK as an external display.

And this just occurred to me.

My 27 iMac works as a monitor for my 24 iMac. But it does not work as a monitor for itself.

However, and oddly. The 27 iMac will send it signal to an external monitor.

The brains of the 27 will show visual to from another computer. And to another computer. But it will now show visuals on itself.

hi guys

I'm having this problem as well.. it's started this week about Tuesday

I've been told it could be "adware" and cleanmymac" and even that its my logic board battery.

so here goes.

i run SSD Fan control

Owly app

using a usb keyboard (a knackered one for the time been)

only using track and a wacom one tablet

disconnected my bluetooth mouse from my iMac in the other room and other things related

i do have all the plugs filled at the back of the iMac

will give it a go

and report back

You can add me to the list!

Since last week I too have a black screen on my 27" 2011 iMac. I have tried all the tips here; fan control, keyboard, singel user, etc. I did a clean install of Yosemite twice and also tried starting up from an external drive, but after just a few seconds my Mac goes black. Connected an extra monitor and that keeps working even if the iMac's screen goes black.

But now for the weird thing: if I start up Bootcamp, the Imac screen is working perfectly!!!

So, it looks like OSX is putting the screen to sleep for some reason, but why is it still doing that after a clean install?

I have had problems recently with the white screen of death. I have a 27 inch iMac, from 2012.

Last September or so I started having keyboard problems. I was getting strange characters when I tried to type. I had an Apple wireless keyboard. Apple suggested it might be a software problem. I remembered that I might have leaned my elbow on part of the keyboard and damaged some of the keys. So I bought an apple USB keyboard. The keyboard came with an extra USB cable, but I did not use it, since the cable coming out of the keyboard was long enough to reach the back of the monitor. The new USB keyboard fixed my problem with inputting characters; however, sometimes on booting up the keyboard would not work at all when I tried to input my password. I read that some users had had this problem and fixed it by just plugging in the keyboard cable USB connector in another USB slot on the back of the monitor. This solution worked for me. Sometimes I would have to boot up one or two more times and try another USB connection slot. After two-three times I was able to input my password and get to my documents, etc.

Last month I had my first experience of the white screen of death. While I was using Power Point, the screen flickered, and then went completely white. The machine would start up, but would never boot past the apple logo. I tried various keyboard commands suggested by apple support and by users, such as Safe Boot, Command-R, Shift, etc., but none seemed to work. I tried DiskWarrior and it may have helped. I set aside my computer for a couple of days and worked on a laptop. A few days later a login screen appeared on my desktop, and I was able to login. However, after two-three days the machine flickered again, this time in a checkerboard pattern, and went out, back to the white screen of death. In trying to deal with this problem, I had read in user support comments that the Command and Option keys on the right side of the keyboard should be used, not the ones on the left side, which I had been using. The right-side Command key plus r got me this time to Disk Utility. I verified my disks, and there were no problems found. I still found that sometimes in logging in, the keyboard input would go dead, and I could not input my password. Changing the USB slot helped a few times, but then it didn't. Thanks to apple support users, I had also read that the Apple keyboard USB connector on the cable coming out of the keyboard sometimes had weak connections with the USB slots on the back of the iMac. So I tried the extra USB cable that came with the keyboard. I connected the keyboard cable connector to the extra USB cable and then connected the extra USB cable to the a USB slot on the back of the iMac. This worked. I was able to login, and I have been using my iMac for two-three days so far without any flickering screens and crashes. I keep it in Sleep mode so I will not have to boot up.

I do not know if this is just a temporary fix or not. Anyway, two take-aways would seem to be:

1) Use the Command key on the right side of the keyboard + r to get past the white screen of death to Disk Utility and

2) Check your USB connections from the keyboard to the monitor and use the extra cable that comes with the apple usb keyboard　　

You can add me to the list too.. Unfortunately.

10- 15 minutes ago black screen with a cursor fail had happened to my computer.

But different from other users, after restart from button my computer started working...

But after a quick search I stated that is a common and urgent matter to all apple users.

And I think not for apple comp.. Sadly.

After selling most expensive hardware on the market around the world, they have to

solve our problems so as their products problems rapidly. 2013 to 2015 there is a

great deal of time to diagonise the problem and fix it both software and hardware

part of product.

I will check it regularly from now on.

(Sorry for my bad english.)