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

SOLUTUION FOR ME!! (maybe for everyone)

i had this problem like a curse for a year. apple services couldnt detect anything. i used to use extentional power supply to protect my imac from power outage harms. i dont use that anymore and i replaced power cord cable with very regular power cord. its not an apple's product even. NO MORE BLACK SCREEN. i know it can be seems irrevelant with screen thing but i dont know. it is working for me. i waited 2 months for testing and observing my imac before write here. everything is just fine. full brightness of course.. i wish a salvation from this blody curse for all of us. byez.

Thanks to the help of other users of this forum I got my problem solved, at least for now (fingers crossed).

My 27-inch late-2009 iMac was working fine since I bought it new until yesterday, when the screen just went black. The day before I watched youtube for a couple hours which I rarely do. My guess is that this caused the iMac to overheat. It started normally, but then the screen went black, although everything else was seem to be working. Tuned off and on a few times, the screen blinked couple of times, but otherwise stayed black. I got the Apple Mini DisplayPort to HDMI adaptor and connect the TV as an external monitor. The external monitor was working, so it wasn't the Power Supply module or the Logic board. I went through many posts on this forum and many suggest to use the flashlight to see if there is image on the screen with no backlight or there is no image at all. In my case, there was no image at all, so it wasn't just missing backlight. I disconnected the power cord and took the glass off then the display itself (there is a youtube video on how to do it). Actually the glass came off without using the suction cups, I just pulled the top edges gently with my fingers. I disconnected all 4 cables and removed the display. Vacuumed all the dust out (there was a lot, no wonder it overheats) from the fans, heat sinks and the bottom screen using the vacuum brush adaptor. One thing that I noticed was the display data cable connector plug (photo from Ifixit website) that connects the display to the Logic board came off very easy, like it wasn't holding well. I tried to connect it disconnect it, it clearly wasn't holding well; it felt loose. I looked with the magnifying glass and it looked like the connector (again, photo from Ifixit website) on the Logic board was a bit curved up in the middle, although everything else including the soldering looked OK. Using my nail I gently pushed the middle of the connector towards the Logic Board to make it parallel to the Logic Board. Then I used the Electrical Contact Cleaner Spray to clean the connector and the display data cable end plug. I tried to connect the display data cable and it was holding much better now. Everything is back together and it worked! No black display and now even the fans don't come on at high speed anymore, I guess the dust was blocking the cooling air flow. I'll update later if it's still working, but I strongly believe that the warped display data cable connector at the Logic Board was the culprit in my case.

Hope this helps!

GL!

Hi There,

Got the black display issue here this morning, on my Late-2012 iMac 21.5" running Yosemite 10.10.4. Never had the issue before today.

Here in South-Western France, we've got extreme outside temperatures a week ago : 40°C and above. In my home office (under the roof) I guess it reached the 55°C barrier.

Being on the road for a week, I just switched on my iMac this morning : Display went black every ten seconds or so, with no reason.

I'm typing this post on my MBA, the iMac before my eyes : Display bright clear, no glitches no dark screen since ten minutes or so.

Like you, I was more on a Software bug rather than on a Hardware problem. Bingo ! Thanks to a guy in this thread - back in 2013 or so.

The fix is very simple : System Preferences / Energy Saver : Display sleep to "Never".

Works perfectly well here.

ps: in the meantime, I've run all the sw fixes explained in this thread : Permission repairs, Display brightness, etc. Maybe the fix is a combination of all that.

Hope this helps,

_Marc

Hi, though I would add my experience to this thread as I also did a lot of reading to see if I could fix the same fault on my mid 2010 mac 27". In my case the screen would go black at random intervals and got progressively worse until the screen would only be on for a few seconds during boot up. Since I am happy to open electronic things (my job) I followed one of the many Youtube posts to have a look inside. Usually these sort of problems are related to poor electrical contacts on connectors so just pulling out the LCD and reconnecting the connectors is always a good start. The video cable has a connector at both ends so peel back the metal tape on the rear of the LCD and reseat this end of the video cable as well.

There is a reported fault with the backlight connectors at the bottom left and right corners of the LCD screen. Again you can carefully peel back the tape and have a look - a gentle movement on the cable bundle will show if the connector has come loose and requires more drastic surgery. In my case the fact that the backlight came on (if only for a few seconds) showed that the LEDs themselves were working and there was some sort of electrical connections.

The steps I followed were:

1) connect remote screen using a display adaptor -> if it works then the graphics card is ok

2) use a torch to see if you can spot characters on the screen. It actually took me ages to shine the light in the right spot at the right angle just near the login prompt before I could actually confirm this. If you can see characters then the LCD is working and the problem is with the backlight board.

3) Buy a replacement backlight driver board (I picked one up on eBay for $40) and install this. All fixed!

Although in this software centric world of apps people always jump to the conclusion that there is a software bug (and I was hoping for this myself) sometimes you just have to accept there is a hardware problem and get the screwdrivers out. For the backlight driver board failure was probably bought about by early aging of the capacitors (high temperatures accelerate this effect so keep those fans clean) or a failure in the pcbs internal connections (vias) which are also a high failure item in pcbs.

So go through the above and hopefully you will be up and away agin. Good luck and thanks to everyone else for your posts which set me down the path to a solution.

I have been working for weeks trying to get to the bottom of my 2008 iMac screen constantly going black.

I tried every fix suggested, in every forum I could find.

I did all the PRAM and SMC resets over and over, I uninstalled and reinstalled Yosemite, I unplugged all peripherals, I installed smc fan control in case it was an overheating problem. I turned off bluetooth etc etc

NOTHING worked.

I was about to give up and resign myself to having to cart my heavy machine down to the Apple store with the prospect of spending a lot of money to investigate and maybe not even fix the problem. But there was one last thing I'd read that I hadn't tried. I couldn't see how it would make a difference but I had nothing to lose so tried it.

It worked!!!

The solution? Try a different keyboard.

So simple but so effective. I was using a wired Apple keyboard with a usb stick plugged into it to power a wireless mouse. I plugged the mouse usb into a usb port in the iMac and plugged in a different (wireless) Logitech keyboard.

Ta da! Problem gone.

I can only assume that the Apple keyboard was causing a glitch (like tripping a fuse) in the display. Different keyboard, no problem.

I urge anyone with this problem to give this solution a try. It's like a miracle cure 🙂

Hi Joe ... It's been 21 days of your new keyboard fix. Is your iMac going black problem still fixed?

I have a 2011 27" Intel iMac and am having the going black problem described in this thread. The only solution I've found - and it may be temporary - is dimming the brightness to its lowest setting.

I read that I'm entitled to a new AMD Radeon 6970M Video Card replacement under a recall program and will be checking into that.

You're all brilliant. Wish my monitor was 😟 Carry on.

I've got an iMac with the same problem! First thought it was a sleep issue and software related, but sure enough there is still a shadow of an image, so thats almost definitely backlight hardware related. Its even blacked out before could get to OS selection. Been scouring the web for a couple days now, and there seems to be a few variations of the issue. Most are summarized in this 15 page+ thread!

-If you don't see a brightness meter, reinstalling OSX will fix, likely a KEXT /driver issue

-A grounding issue in which a new UPC cable does the trick.

-Even a faulty keyboard, maybe sending a sleep command, or some sort of monitor brightness function.

-But for those with the stubborn back light dropping out, I would say things point to the backlight board. But that only seems to work for some, so were left with one more known possibility - there is a confirmed problem with the V-Sync cable connector on the display of 27" iMacs of your erra. That is, the socket, not the Cable. Over time the solder on this connection breaks up. The reason frequency increases in black screen while the computer is on, is the joints warm up and expand, and disconnect. Although this known issue in 27" iMacs is more popular for manifesting itself in other ways such as a half dim screen, its possible that this faulty connection could result in a total black out. Repairing it in that case, is unfortunately pretty tricky and requires some pretty extreme soldering skills. From what I hear, Apple protocol is to replace the whole screen. Which I get when it comes to amount of work and tools it would take to repair. Hope that helps any other pour souls with the same issue! I personally am going to try a new backlight board, just in case.

Hi Ryan - Did you change the backlight control board and did it work?

For the sake of adding my name onto the long list of owners of faulty iMacs ... I also have a late 2009 iMac (2.66ghz i5) bought new in 2010 with the same "black screen" issue. The issue started to appear very randomly in May 2010 just after my applecare ran out; I initially thought it was a software issue of some sorts and as it was a random fault did not take any actions other than keeping my eyes and ears open for possible fixes and avoiding to use the iMac much.

With time the "Random black screens" became more frequent and the iMac is now only usable at a brightness of approximately 4 bars maximum, above this the screen goes black within a few seconds.

What are the symptoms:

- Randomly the screen gets black. Initially the fault occurred every few month but could some time happened repeatedly in quick succession on a single day, making the iMac unusable on this day. Nowadays, the fault is much more frequent if the display brightness is set above 4 bars (Roughly 30% of the Maximum possible) and this appears to be reducing with time.

- The computer continues running as normal when this happens - There are no events/errors in the logs.

- The image is still visible on an external display and the computer can be operated as normal.

- Shining a torch on the black screen shows the actual image is there in the background.

- The black screen can occur when the computer is starting up (even before the log in screen) and is cold or later and does not seem to be temperature related.

- As I do not see any glow on the screen when it turns black, I assume that the backlight is off.

- An extended diagnostics check identified no hardware issues.

- PRAM and SMC resets did not solve the issue.

- The screen can be "awakened" by using SHIFT CTRL Eject + any key or by putting it to sleep and waking it up again. I set-up a hot corner at this effect.

- A screen recording of the screen during blackout using QuickTime player does not show any blackout. The screen looks normal as per the external monitor.

Next Steps:

As I am interested to know exactly what caused the issue, I am taking the iMac to a well reputed electronics repair company for a full assessment tomorrow and if they succeed in tracing the issue to a specific component or connection I will report back on this thread and hopefully help others with the same issue who may be looking at keeping their old iMac for a bit longer.

As a side comment, I would point-out that the Apple certified resellers/service providers were mostly interested in changing parts until eventually they got (or not) to the right one; a way to operate that is fine when an item is under warranty but that can be extremely un-economical for an out of warranty item. Add to this, the diagnostics cost and it is a potentially very pricy repair! I was even told by one of them that I got good use from the iMac so should not have anything to complain about! OOPS! I guess I need to stop being a laggard! 🙂

I have done a lot of reading on this, as I have a Late 2009 running yosemite 10.10.5 with this problem. Here is a summary of what I have found.

1. People are often told to reset the pram and SMC but these rarely, if ever work.

2. Some have found that changing peripherals, such as the keyboard solves the problem, especially if the genius bar was unable to replicate the black screen when the computer was left with them.

3. If you use an adapter to plug in an external monitor and it works, your graphics card is not the source of the problem. Be sure to been running the operating system, as the installation process, or apple hardware test do not drive the external monitor.

4. Apple hardware test (start and hit D) will usually not report a problem. Some have reported the need to run the extended test three times in a row, but I have not seen anyone reporting success through this method, and it did not work for me.

5. The problem is progressive and becomes worse over time. Some have had success using the keyboard or hot corners to put the computer to sleep and wake it, to get the monitor to function but this only works for a while, and no longer works for me.

6. Some have reported success simply by detaching the video sync cable (the first cable you have to remove when opening up the iMac), but this did not work for me. Leaving the sync cable detached did not cause any problems in running the system that I could note. Others have reported success by removing and reseating ALL of the cables inside the iMac.

7. Most, including me, get the best success by turning down the brightness of the monitor. I can run for at least several hours with the brightness turned down, but the screen will black out almost instantly if I turn the brightness up beyond about 25%.

8. Some have reported success by replacing simply the LED control board, which is different from the graphics card. This is the board that the video sync cable is attached to. There is no actual backlight on LED displays so a failed backlight will not be the problem on this era of computer

9. Others have needed to replace or repair (see motorcycle Michael's post on this, above) the entire LG LED panel to solve the problem.

10. Some have been able to see the display by looking very carefully at the display while holding a strong light to it. I am not sure what this tells you however.

11. Heat and cleaning the fans does not help me, but some have reported getting longer by installing a fan controller program. Again, this did not work for me; No matter what the temperature, turning up the brightness will eventually lead to a black screen.

So, as things are right now, according to the above, I either need to keep the display dimmed, replace the LED control board (also sometimes called the inventor board), or replace/repair the monitor. I know of no way to determine which will solve the black screen problem on this iMac

@Murrfk: About Point 10: if you can see the desktop then it is the backlight which is off, and the actual screen is not the problem.

That might be true for the screens that have a backlight, but mine, being a LG LCD (I mistakenly typed LED in my previous post) does not have a backlight. So perhaps the flashlight test is not useful for screens that don't have a backlight?

Also, I did read where one person felt the problem was solved by removing incompatible memory, and I failed to mention that in my previous post.

My display blackout issue (As per my above comment posted on 1 October 2015) has been diagnosed as a faulty LG LCD Display (LED strip)... Unfortunately not a cheap fix as the display unit needs replacing. I would guess that the majority of the screen blackout issues (Partial or intermittent) were probably caused by the same design/manufacturing issue with the LG LCD display.

That would suggest that Motorcycle Michael's fix might be useful. I haven't tried it yet, as I am kind of learning to live with it.

Hi guys,

The screen blacking-out started happening to me just yesterday. I could still hear faint mechanical sounds from within, so I know that the computer was still running. I was able to get the screen working again (for not too long) by unplugging the computer and then plugging it back in, and then restarting it. But the blacking-out situation would soon re-occur. I intuitively sensed that the screen was "shutting down" for self-preservation reasons, and tried lowering the brightness level to about 35% ... quite dim ... but if I nudged it up even a bit more ... click-blackness.

I managed to read all 16 pages of this. Oh ****.

But then I had a minor flash ... actually two flashes. It seemed to be putting itself into some kind of sleep mode, but a sleep mode from which it couldn't be awakened in the usual way. Somebody suggested adjusting the sleep timer to *never*. I had enough technical expertise to do that do that, and then I would use the slowest smallest simplest darkest Screen Saver instead. But I was a Science teacher, and I started thinking back a day or two ... wondering what might have changed with the computer ... and I suddenly remembered that yesterday morning I'd had to replace the batteries in my wireless ... KEYBOARD! And at least two people in the thread had commented about switching-out keyboards! Hmmm ...

So I turned off the computer. Removed the new batteries from the keyboard ... confirming that ... yes ... they were placed in correctly. I fired up the computer and returned the batteries and turned on the keyboard (which connected immediately) and boldly set the monitor's brightness to a very workable 50%. And that was 30 minutes ago. in a coupe of days.

Still goin' strong ...

Two variables were monkeyed-around a bit, but the Screen Saver hasn't even had a chance to kick-in yet, so I am thinking that the simple disconnect/reconnect of the keyboard might have done something. Your mileage may vary, but it's worth a shot. I'll report-back in a couple of days.

Well, it's morning now. The screen saver was working when I went to bed, but ... uh oh ... black screen is back. I restarted the computer and set the brightness back to about 48% and poof ... in three seconds the screen went black. I quickly restored it with keystrokes and rushed to turn down the brightness level but poof it would go black within a few seconds. So I turned off the computer and removed the keyboard batteries and restarted the computer. With the dead keyboard sitting here, I went to the brightness level and moved it to 50% ... in three seconds it goes black. Restart the computer and connect the keyboard and it loads in at 30%, but it's functioning. So now I'm gonna try to move the brightness to 45%, to see if I can duplicate last night's relative success. Fingers crossed. Here goes ...

(To be continued ... )