iMac 27" Black Screen?

Are you using another Bluetooth key or USB?

6hrs and still good, was crashing every 15 mins before

Hope Apple figures this one out soon... I don't have another keyboard

Guess I'll go buy one later... 3 days is pretty good ...

Mine turned out to be a software issue. Machine would boot up, could hear the hard disk. Screen stayed completely black. Went to Radio Shack to pick up an adapter, hooked up antother monitor, it worked - so - whew! - it isn't the graphics card.

Main screen had been down for two days. After hybernating - it came back to life. I had the display back. Soooo... it was a software issue. Lion has been sort of dicey with hybernation from day one... I thought about attemting to find and replace faulty Kext files - but who's got time to dig around and find out where the issues are. Shouldn't Apple be doing this?

I upgraded to Maverics, and bingo! No more dicey hybernation. No more black screen. Issue solved.

This problem has got me – and Apple and their technicians – intrigued because of the variety of so-called fixes. After talking to Apple (Sydney) and the local tech for about an hour, this is how I understand matters:

1. The fault is not directly software related. Nothing to do with suspect code, except if the code somehow affects (in a significant way) a physical attribute inside the computer, such as voltage, current, or electromagnetic radiation (EMR), and that change in attribute causes the fault to occur. Brightness variation is just such a change because voltage levels undergo significant variation as brightness is altered. But the code itself cannot be blamed.
2. Not directly related to heat, either. The tech stated that the fault is more likely to occur cold. As an example, he blocked up the vents while testing a particular machine, ran a processing task that consumed all the CPU power, and watched while the Processor Temperature Diode (I think) ran up to 98º – but no fault. He also runs cold tests.
3. Could be related to the amount of EMR being emitted in certain areas of the video card. He gave an example (from his radio repair days) of a copper track making a right-angle bend on a circuit board. At the sharp point, radiation will be emitted much like from an antenna. The amount of such radiation will depend on voltage, current, and frequency of signals on the track, and may affect – cause arcing – in areas close by.
4. Apple's engineers may have an inkling of what the problem is, but if they do they are not sharing the info with technicians in Australia. The particular tech I was talking with has been pushing Apple for more info, and offering them as much info as he can, but in his words: "I've pushed and pushed, but until Apple engineers find what the problem is – nothing". He is still pretty much working in the dark regarding this fault. i.e. there is no definite fix as yet that points to a definite connector/component/track/whatever. They fix mostly by changing the video card, but other fixes can also appear to work.
5. Apple may not give the go ahead for repair until the problem is seen to occur AND the problem is detected by an Apple on-line diagnostic program, something called VST on the Apple Diagnostic Server. The tech hooks up the faulty computer, and based on the serial number of the computer a specific test is run.
6. It is possible that the computer can be faulty, but the fault not be picked up by the diagnostic test. From Apple's point of view that creates a problem. They would like to be able to fix the fault (which at the moment can't reliably be detected) by a defined series of steps (do this, do that), otherwise they are inefficiently spending money on repairs. But they also want to keep their customers happy. I can understand Apple's point of view. If the problem hasn't been definitely located, it is not sensible for Apple to simply replace all video cards on the off chance the problem may be fixed.
7. The tech said he is getting better at the diagnosis, but he still has to see the fault occur and have it detected diagnostically. He can't repair until Apple gives the go ahead.
8. Supporting evidence by means of a video of the fault occurring, preferably several in short succession, is good evidence which Apple may accept in lieu of the diagnostic test.
9. Affected computers are subject to a worldwide recall, iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support

To sum up: by all means experiment with various software fixes, but none of them go to the core of the problem. The problem is in hardware, but software can appear to fix the problem if the software changes some attribute (voltage, current, EMR), in a way that may be different from another piece of software trying to do the same thing.

Hey there, I tried a different keyboard (usb from my pc) and I STILL have the same problem (screen going black), exactly the same problems Rixxi had, except none of my parts have been replaced. I'm using an smh... I've had this problem since I upgraded to Mavericks. I did not use Time Capsule (I should've), so I lost Mountain Lion. I re-installed Mavericks and still have the same issue.

Unfortunately the keyboard changed fixed the problem for a couple weeks, taking it in (jostling?) the computer fixed it for a couple weeks. Right now I feel like I'm just trying things the way one tries superstitions. But someone else had an answer that makes sense to me, but it's expensive or difficult to fix.

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.

I could find the main cable from the display to the logic board to replace, and that didn't fix it, but I couldn't find the cable from the backlight board to the display itself (outside of a new display) so I'm convinced its the connection with that cable.

I don't think its temperature related, I think its just a bad connection somewhere on one of those ends.

PS My replacement display (which is actually just a display pulled out of another "recycled" system, is still fully functional after almost 9 months of use."

https://discussions.apple.com/profile/pbook4g5

https://discussions.apple.com/thread/4053857?answerId=25054120022#25054120022

Hola,

2 months ago I had the same problem. I was working one night on my iMac (27' inch 3.4 GHz Intel Core i7 4GB Mac OS X version 10.7.5) and boom, my screen went black, but the music in the background still playing, so I thought it was the heat because I've been editing photos all day, so I turned it off and turned it back on again later that night, and the screen was black, I couldn't do anything.

I read this threat a lot, and did everything you guys said, but nothing. I even thought this replacement program was for me. So I took it to an authorized store and they said it was my logic board and it needed to be replaced and it would cost me $700. I didn't find that diagnostic logic because my computer was working, only not displaying anything, I could work with an external monitor or video beam, and everything was fine. So I took it to another authorized store in a different city (Mac Center, Medellín), and they said it was the backlight what need to be changed, so they ordered a new backlight board (part 923-0047) which costed me around $300 with installation.

Its been a week and so far my computer is working fine, no black screen. If something else happen I'll post it. But for now, that was my solution.

I had these same sort of issues and tried everything. Turns out it is a known issue and Apple has a replacement program for the bad video card in many iMac models. The bad card causes grey screens, black screens, sleep issue, hard drive slowness, system spins, kernel panics, and more! Wow, all fixed at no charge at my local Apple Store!

See:

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support

I'm having the same issue recently (older iMac 27, Mountain Lion), though the iMac does not really go to sleep. It's only the screen that turns itself off randomnly, the Mac is still awake. To get it back on, I use the key combination alt-cmd-eject to actually put the iMac to sleep. Hitting any key will wake it up with the screen turned on again. Annoying. Can't find an answer so far as to where the problem is coming from.

I replied in another thread but it applies here as well. I think it could be the keyboard.

I had the problem recur 3 times exactly the same, screen goes dark, computer is still on as the audio works. Twice the genius bar failed to find the problem.

Then I realized they use their own keyboard when I take it in. The keyboard has a brightness control, so it's not completely illogical.

I have a new keyboead and so far the problem has not recurred.

The bigger question is why hasn't Apple figured it out yet?

I'm on day three with the alternate keuboard, no repeat of the problem. I'm going to have to use this one for a couple weeks and if the problem doesn't recur, get a new keyboard (this one is klunky). Please do let me know how your experience progresses. I appreciate it.

I'm using my old keyboard from a PC that I replaced with the IMac. It's wireless but the signal is from a USB connected device and it's not Bluetooth. I removed the batteries from my Mac keyboard to assure it was off. It's the one that came with the IMac. You can turn it on, but hitting the switch again just turns it on, not off as far as I can tell. So I took the batteries out.

How are you typing with only a mouse?

I'd suggest waiting to see if the keyboard is the problem by buying one of those really inexpensive ones to use for a while before getting another nice one.

Also, I'm considering taking the keyboard in to the genius bar. Around here Apple doesn't charge for diagnosing, only for fixing if you are off warranty.

The more I think about it the more nervous I am to use the problem keyboard. I don't know if it's possible it might make the computer unbootable or unable to stay on long enough for me to switch back to this keyboard.

And speaking of that, do you have a model with the recalled hard drive? Mine was. That wasn't the screen problem but the hard drive was failing when I took it in. They weren't going to give me a free replacement because the window for getting a new one had passed. I put up a fuss and got the free hard drive replacement. After all, it was a recalled part.