Currently Being ModeratedOct 13, 2013 6:36 PM (in response to Stepppy)
Same here, it has been about a year or so that the screen started going on and off. found by increasing the brightness has reduced the frequency of the screen going off also when the screen goes out by pressing ctrl-shift-eject several times brings the screen back on. Hope this helps, and apple should fix this either by software or hardware replacement.
Currently Being ModeratedOct 13, 2013 10:16 PM (in response to Stepppy)
Same problem started about a year ago. 27" iMac bought around end of 2010. Apple please do something to fix this!
Currently Being ModeratedOct 15, 2013 6:16 PM (in response to Julian Yu)
Read thru practically all of this 8-page thread and for what it's worth:
Dealing with a 21" early '08 iMac 2.4GHz running 10.8+ that has same symptoms, namely black screen with data barely visible using a flashlight. Used to replacing inverter boards for problems like this, but installing a brand new board didn't change a thing this time; it's the backlights, not a repair for the faint of heart. The 21s have backlights top and bottom, and this one flashes momentarily on startup (sometimes), then top half blacks out a milisecond before bottom one goes. External monitor lights up and works fine, except that it's useless without mirroring.
To jjhaffner - THANK YOU for that keyboard trick for switching monitors (control+shift+eject, 2nd entry in thread). We lost the F7 mirror key long ago and command+F1 doesn't work under 10.8 either. Couldn't find a keyboard command for switching/mirroring displays anywhere!
Can't seem to find the 21" version of this thread either, but I'll keep looking..... or start one. ;-)
Currently Being ModeratedOct 19, 2013 7:16 AM (in response to Stepppy)
Hi everyone. Just thought i would add to this post like many others. I have, at work, a 27 inch i5 imac (mid 2009) and untill recently has been working faultlessly. I had it at my house for a year then i took it to use at my business (kitchens and bathrooms if anyone is interested....haha) i run windows 7 via bootcamp on it too. Now, today in my showroom i was using the computer (on windows) and the screen went black. Everything was working ie hardrives and wotnot but the screen went black. I have read through the entire thread and have already tried the smc reset and the pram reset and have also tried the slight pushing of the power button( this occasionally brings the display out of sleep and back to reality as it were). I think all i am trying to say is that this problems isn't just linked to later models ..... i will however, try cleaning all of the fans because windows 7 does run very hot via bootcamp and the machine has never been opened and i am pretty sure that if it is a heat related issue this may be sorted.
Will keep you posted.
Currently Being ModeratedNov 14, 2013 1:17 PM (in response to Fozzy155)
For what it may be worth, replacing CCFL backlights within (early-'08) display fixed it. These are .095" outside diameter glass tubes, very thin-wall, long and extremely delicate, very difficult to replace and not recommended. There are two on each side of 27" or two top and bottom of 21" displays. Failed tubes were blackened on ends, just as any other burnt-out fluorescent tube.
LED displays do not have these, used on older LCD displays.
Fozzy155: Your mid-09 iMac has an LED display. Cleaning interior and re-seating connectors might solve it. If not, your machine has an LED driver board that is next suspect.
Currently Being ModeratedNov 14, 2013 4:15 PM (in response to Fozzy155)
Just replaced LED backlight board on a 27" mid-09 iMac with screen blackout problem. No change, still blacks out, so..... so much for that idea. Display or logic board. Exact same symptoms; with "Power Button Sleep" option on, a quick double-press of power button brings display right back. Sorry Fozzy. :-(
Currently Being ModeratedNov 30, 2013 5:29 AM (in response to Motorcycle Michael)
Hello, I wanna contribute something to this thread. I have an IMAC OSX 25" Just upgraded to Mavericks. It was released last year November 30th so It will still be a year old tomorrow. My black screen problem started about six months ago. Itwould go black while am using it then will come back after like few seconds. This would happen only rarely. It scared me the first time but it stopped so I forgot about it. But today, when i got home, my screen was black as usual cos I set it to 1 minute display sleep. computer sleep: never. So i click the mouse then the screen came up. But after a while like a minute it will go black. this goes on and on. just randomly going black even if am using it. The computer seems to be working just the screen is black. it was annoying. So i decided to shut it down in the hope that twas prbably due to overload. I hardly put my cmpter off.. But to my dismay, its still the same. I changed the setting for my display sleep to never. and shutdown my computer, still the sme. I can open the computer, still working but the screen goes black every after 1 minute, and it will only goes back like after 3minutes despite clicking my mouse. But instead of shutting down the computer i tried restarting it this time. And thank God. It was back to normal. Well it was only an hour ago and it still okay until now. Hope this helps.
Currently Being ModeratedNov 30, 2013 8:19 AM (in response to Stepppy)
Well, I posted here about the black screen back in the summer. It could be delayed by resetting the PRAM/NVRAM and reducing the brightness. But eventually even this did not help. So in August we had a whole new screen for around £400/$600. All has been well until now.
On Thursday it started going black again. I can't identify anything likely on the Console log, but I'm no expert. It happened three times. It came back after restarting the computer each time. Yeaterday and today the computer has been on all day and the screen is fine....so far.
The failure is not a general power problem, al the other equipment and electrics in the house are working fine.
This is just annoying now. I've had Apple stuff since the Lisa in 1982 and this is the first bit of Apple stuff that has gone wrong, but it was closely followed by the failure of the trackpad on a 2007 Black MacBook. Is this a sign of things to come?
Currently Being ModeratedNov 30, 2013 11:31 AM (in response to aero280)
Swollen battery under trackpad was most common cause of trackpad problems with those plastic-case MacBooks, but that's another discussion.
The display problem addressed in this thread is not Apple's fault but belongs entirely with LG.
Assuming yours is a 27" iMac with LED-backlit display LM270WQ1 (SD) (A2), and display is not going to sleep but actually blacks out (data is barely visible on black screen with use of a flashlight), here's a workaround and a possible fix.
Workaround: Open System Preferences > Energy Saver and check the box marked "Allow power button to put computer to sleep" (if it isn't checked already). When screen blacks out, press power button once, wait a second or two, then press it again. This puts machine to sleep then wakes it up, somehow restoring backlight. Don't know why, but it seems to work reliably.
Possible fix: Potential for doing severe damage to iMac's logic board is enormous, so I don't recommend this process as a do-it-yourself repair. Removing machine's display requires disconnecting four delicate cables, two of which have retaining clips. Damage to any of these four connectors = disaster. If you're capable (and brave enough) to remove machine's glass and display panel - take apart instructions may be found online - the problem appears to be with a pair of tiny gold-plated backlight plug/socket assemblies on LG display. With display removed and placed face-down, you'll find a pair of six-conductor ribbon cables sharing the backlight plug to backlight board. Carefully removing tape covering these two cables will lead to plug/socket in corners of display. Here's one:
Plugs are held in their respective sockets by a white plastic retainer; retainers have tabs that must be cut off in order to remove the two black plugs. Once retainers are out of the way, plugs may be carefully "walked" out of their sockets using a hook-shaped tool (tool shown was made from a piece of .062" rod).
Just removing and reseating these plugs may solve your black-out problem; depending on how tight or loose they feel, this may be all that's needed. Otherwise, adding a thin plastic wedge may help them maintain contact, or perhaps a dab of silicon dielectric compound on pins might help.
Again, these are very delicate connectors, as are the ones behind display, and this fix requires some expertise and special tools. Proceed at your own risk!
Currently Being ModeratedNov 30, 2013 2:26 PM (in response to Motorcycle Michael)
Thanks Michael. I do however, have a few problems with your post.
First, you say "fault belongs entirely with LG". I am sorry, but I did not buy my iMac from LG, I purchased it from Apple. It is their sole responsibility to deal with any fall out of supplier's defective parts. They have to stand behind the product they sold me.
Second, on your DIY solution, how did you come up with this if you don't mind me asking? Did you try it yourself? Did it actually help the problem? If so, have you been running blackness free for at least 6 months? I find it very hard to believe a plug, with tabs that need to be cut off to be removed and that sits unmoved and untouched, decides to loose connectivity all on its own. If an iMac sits still, not moving on a steady surface, and the plug is the problem, it'd either work or it would not.
I think it is a far more logical and simple explanation the display board is bad. As others have already replaced the LCD and the bulbs to no avail. I have yet to see anyone replace the board on their own and share results.
Sorry, but I believe Occam's razor applies to this case.
Currently Being ModeratedNov 30, 2013 2:51 PM (in response to Winchy)
I'll chime back in here, as I'm still running blackness-free for 8 months now (or whenever I changed my LCD board with another one.)
I changed every cable BUT the black one, because I couldn't find a replacement online anywhere. All of the other cables, though, I replaced. So, I do think its something with that cable or the connection that it shares with the backlight board and the display itself. Having replaced the backlight board (twice) I don't think its on that end, so I'd also say its on the connection on the display itself.
Since I never took mine apart to look at it, I might just do that (since I still have my old display).
Heat could easily cause the connector to become loose, as they aren't the best type of connectors as far as snug fit goes.
And Winchy, the main components discussed in this thread are the display (with backlight all in one), the LED driver board and the logic board/power supply, etc. I replaced the backlight board twice, all of the cables that hook to it once and then I replaced the display itself.
There are no bulbs to replace here, at least not with the displays in question (older displays, yes).
Currently Being ModeratedNov 30, 2013 3:33 PM (in response to Winchy)
Fault is LG's in that an otherwise spectacular display can be brought down by a too-tiny and even unnecessary connector. Apple, like every tech company, depends on its suppliers to some degree.
Solution only applies to this one, specific LG display. Clearly _not_ a DIY solution, I arrived at it by testing and tracing the problem - basic troubleshooting - which is what I do for a living. Start with any "quick fix" that may apply, then progress logically thru the more complicated possibilities. Having eliminated everything but the display itself (incl. video card and LED backlight board - no CCFL "bulbs" here), these connectors were the next - and as it turned out - last suspects. To my knowledge, no one has ever fixed a computer using philosophy.
If you indeed do have the specific problem which is the subject of this discussion, take your machine to Apple and they will most likely replace its display. If it's some other issue (and there are a myriad of things that can make a display go black), they will certainly find and fix that, too. I just couldn't see wasting a fully-functional and stellar 27" display over an intermittent connection.
Currently Being ModeratedDec 1, 2013 10:34 AM (in response to Motorcycle Michael)
If others are having what appears to be boot up problems with a gray or whites screen and have a '11imac
Make a Genius Bar appointment. It's probable you have a bad video card. It's about a 290$ repair, but apple has acknowledged it as bad design and fixes it free even if not under warranty.
Currently Being ModeratedDec 22, 2013 3:14 AM (in response to Stepppy)
I am having same issues. Although I usually use my iMac 27" mid 2011 in bootcamp windows 7. I have had it now about 10 times in the last week that all of a sudden the screen goes black but the computer still works. I just press the power button so system shut down itself and when I start it up again straight away all is fine again.
I have send it to a apple repair centre. My iMac flew through their test, so they didnt find anything.
When it happens again I will do that test with the flashlight in dark room.
Currently Being ModeratedDec 22, 2013 3:45 AM (in response to AlexJ2013)
Just had the black screen happen again. Now tried to see if I could see anything on the screen using a flashlight. I was using windows 7 and could see the bar and start button on the bottom of the screen. So I don't know what this means now?