Q: iMac 27" Screen goes black repeatedly, but then settles for a while?

I can only detail what I found with ours.  The black screen has been a problem for nearly three months.

First we found that the screen could be kept working by lowering the brightness.  Eventually though, even on minimum brightnesss, the screen started to die again.

I was advised to try a PRAM & SMC reset.  I did this and the screen came back on full brightness for a while. But the problem was still there with the black screen occurring more and more frequently even with us reducing the brightness.

We tried another PRAM/SMC reset and again it recovered for a week before failing again.

Throughout this time we were able to access all the files stored on the iMac by looking over the network from the laptop. 

We also tried shining a light through the black screen but there was no sign of any icons hiding in the dark.

We took the iMac to the Genius at the Apple store and it passed all tests.  We eventually decided that the best solution would be to replace the whole display.

The iMac has been home for three days and has worked continuously since its return.  Time will tell.

My reasons for agreeing to a replacement display?

The screen had no icons, so it wasn't just a backlight failure.

All the files were visible over the network at all times, so any fault was not with the HD and its controls and I/O system.

And with the computer bit working the power board seemed OK.

That just left the display.

read my previous post with the link i've attached just before yours.  call & inquire with apple

@Berniedmj

No, that is for a different and very specific problem that affected certain models only. The display going to sleep is not one of them.

Sorry Berniedmj, completely unrelated to this problem. That is for an entirely different issue. As a matter of fact I had already called them about this when this article broke out a few days ago. Apple care told me they are only doing Mac Pro's for now, but I could see if my local store may have a different view. So they made me an appointment anyway since I had already complaint about a year ago. So here I go again...

My iMac does fall within the serial numbers that are bad, but I seriously doubt, even if they replace the card, that is going to fix the darkeking, flickering, blacking out problem this thread talks about. This is a more serious hardware issue I doubt Apple ever man up to.

Sadly that recall program is for the 2011 on models with the Thunderbolt connector.  Our iMac is a mid/late 2010 model that is not covered by that program.

read the link i've attached & get happy

http://www.cultofmac.com/241213/apple-launches-replacement-program-for-27-inch-i macs-with-graphics-problems/

Well, sorry.  I thought it only happened to the models in between 2011 & 2012. That's why I said the majority rather than everybody. Mine was pertaining to that article/forum & mine was fixed.   Good luck

Winchy -

I asked a nice Mac parts dealer on Ebay if he could narrow down the list of suspect parts - I was assuming that he had heard of this problem before, etc. He told me that the actual service manual, the one they give to "apple certified" technicians, says, more or less "replace this part, if it don't work replace this other part, if it don't work replace this other part..." etc. So yes, your impression that the experts don't know what the **** is going on is spot on correct.

It sounds to me like, if you can see an image through the display using the "flashlight test", then it's the backlight, which means it's either the inverter - the board which drives the backlights - or the backlights themselves, which, unfortunately, are built into the LCD (but NOT the fans, the logic board, the graphics card, etc.) No way that I know of to test which of those 2 components short of swapping them out with new ones.

If any of that sounds incorrect or substantially incomplete, please could anyone correct or fill in?

And, Winchy, what model/year machine you working on? "Cause if it's a 2009, you might get away with about $300 in parts all in (if you have exactly the problem I have and no other problem). If, like me, you have a mid-2011, I think it's going to be hard to escape with less than $800 down the pipe, but I've not yet purchased the LCD, gonna do that today unless someone convinces me I've got it all wrong. And if you've got a 2012, you might as well take it in 'cause it's gonna cost you a big bag of cash anyway...

Good luck and thanks for the input, all...

Just to tidy up a bit.  I'm in the UK.  The new display, fitted by the Apple guys at the Apple store, came to £434, or $680.

27 inch iMac 3.2GHz Intel Core i3, was purchased new in December 2010.

Jerry, yep... I have that service manual, which is why I took the steps I did in remedying my issue.

This may seem hit or miss, but really, its the same thing the techs do.

For what its worth, if replacing the LCD didn't solve my issue, my next step was the logic board and then the power supply.

Luckily, I'm fairly confident it was the LCD/Backlight itself. You can find them for the 2011/2012 machines on ebay for not too much money, so don't expect to pay a big bag of cash for one.

Good luck.

pbook -

I've just been told that, if the problem doesn't extend to an external monitor, it's just the built in that goes black, that eliminates the logic board as the source of the problem. I found a guy on Ebay who will do a replacement LCD for $550 (which in my world is a big bag o cash) or $350 with a trade in - which suggests that there IS a way to repair the backlights...

Ours is now 2 weeks in and the new display is still working.  Fingers crossed...

So a quick update on my apple repairs...

I took the iMac back to the geniuses to have the Radeon replaced under the recall warranty. Hoping that in some way, was related to this issue, but internally knowing it was really not related. But it wasn't going to cost me anything and my serial number was within the defective range so I figued, why not?

Well the first you all need to know is that EVEN if your machine matched the batch that had the bad Radeon, they do not go ahead and replace it blindly. They run a video test that looks for a particular signature the card put out when it contains the problem. Mine came out clean, so off course, they refused to replace it under warranty. I went through my shpeal of how many problems I have been having with the screen and how many times I had been to the bar to try to solve it that, I guess, they felt sorry for me and after a quick chat with the manager behind close doors, he agreed to replace it. Quoted the repair to take 5 days, but I got a call the next day that it was ready for pickup.

I arrived all giddy to get my baby back. Something inside of me was still hoping it would have fixed the dimming and black out problem but... once I got home, sure enough. Not 10 minutes into a working session, there it goes again, the flashing, the dimming, the flickering and in a month or so, the black screen, that is for certain.

So, like I had stated before in this thread, the recall on the video card has nothing to do with this problem that so many have experienced and Apple does not seem to want to acknowledge.

BTW: The total cost for the card swap was $265.14. All on Apple's, and it wasn't even needed, So can't really complaint "too" much!   Genus also re-stated that, for fix the other problem they would start replacing part by part until there was no more parts to replace until it was fixed. I really wanted to cry, but I didn't. I mean really, what kind of computer manufacturer does not what the problem is with their own equipment? What is up with the guessing game?  Off my soap box now.

Hi guys!

Just wanted to add to this discussion to keep it going AND HOPE APPLE NOTICES. I have recently experienced the same thing. I would switch on my iMac then it would black out. The shift+control+eject would momentarily bring back the screen sometimes but it won't work all the time. Also ruled out other problems like temperature, etc. Logically, if it were about the hardware then the screen won't even come back at all right. Also executed  SMC and NVRAM/PRAM resets. The PRAM reset would help for a while then the blackout would still occur when it has dimned. My system can boot to another partition and in Safe Mode but the blackout would still occur after a few seconds. I guess this points to a software problem, maybe the firmware of the screen perhaps? Currently exploring the possibility that it might be a dirt problem in one of the heat sensors.

I just chatted with Apple support and insisted it was a software problem. Even with more than 30,000 views on this thread, they couldn't even acknowledge the problem. Thinking my next computer won't be from Apple.

The left half of my screen started to occasionally darken and now my screen will just go blank with no warning.  I was able to get it to go back on by hard booting.  But it is starting to happen more frequently.  I read through part of this thread and it sounds similiar to the recall issue but I have the AMD Radeon HD 6770M in my 27" iMAC.  So I assume this is not included in the recall?