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

I picked up my iMac today from Apple. They replaced the LED backlight boards. I've been using it non-stop tonight (about 6 hours straight) and have not experienced any problems. Everything on the Mac is how it was, the drive was not erased for a Lion reinstall. So far so good. If it starts acting up, I'll post another update.

Yes, I agree, my original comment was misworded.

Here's a link: http://www.hddfancontrol.com/imac-hard-drive-replacement-fan-noise-issue/

This is a problem that a lot of people have with not only the iMacs but with some Mac laptops, particularly the Macbookpro.

Apple started using harddrives that required a temperature sensor. The sensors monitored the temperature and when the iMac (or some Macbookpros) got too hot the fans would kick on. However, Apple used some really cheap Chinese harddrives in some of their iMacs. These had a high failure rate with either a complete failure, or the temperature sensor malfunctioning. When people whose harddrive had failed completely replaced them they replaced them with hard drives that did not have a temperature sensor. This caused the fans to not run, or the mac to think it was hotter than it was and to make the screen go black, make the fan stop, etc. You could click the mouse and the iMac would start back up. But, the symptoms would appear again, fairly soon.

I made an appointment at the Genius Bar and took my iMac in. They had it for a week, but iMac did not go to black. While I was picking up my iMac one of the technicians came out to talk with someone. He was wearing a jacket. I went up and asked him why he had on a jacket and he said they kept the tech room really cold because there were so many machines on. Of course, that was why my iMac wouldn't fail even though they had it running 24 hours a day for almost a week. The room was too cold.

I took my iMac home and within hours it failed. I decided to turn off the heat in my place, bundled up, and waited. The place got really cold and my iMac didn't fail the rest of the day. It didn't fail the next day either. I turned the heat on again, and it failed. I did some research and downloaded one of the free fan controllers. It work somewhat. I discovered that my iMac would fail at 54° C and above (the fan controll listed my iMac temperature in the top menu bar). That was the cutoff. I put a fan behind my iMac and ran it and watched the temperature go down to about 49°C. It didn't fail. I turned off the fan and watched the temperature go up. It failed again at 54°C.

A lot of people on some other forums figured out what was happening and came up with various fan controllers to solve the problem. Most are free. I've tried them all and they worked sorta. But, my iMac was still going to black occasionally. So, I broke down and bought the HDD because people on another forum said it worked for them when the free ones didn't. And it worked for me, too.

Goto this link. Apple put this out! Hopefully this will resolve everybodies problems. Let just say, if you put money into fixing your issue... Apple will refund you!! It's real. Just read the link I attached

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

Now that heavy weight is off your shoulders!!!

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!

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

LONG-TERM FIX and SOLUTION: If you've read this far and still haven't been able to fix your screen from going black, please go back to Page 8 and reread this post by Motorcycle Michael, and subsequent responses by him and pbook4g5.

I've been following this thread for several years as my screen has exhibited this problem on and off. I've tried many of the suggestions that were logical, including installing smcFanControl (heat issues) and reseating and cleaning each plug inside the computer with electrical contact cleaner (connection issues). None of these solutions provided a long-term solution. I didn't even try reinstalling the OS (it's not a software problem), or zapping the PRAM and all the other voodoo suggestions (illogical conclusions).

My black screen continued to get worse to the point where lowering the brightness to zero was the only way to keep the screen alive. As a designer and photographer, I needed to see my image and could no longer rely on the histogram alone. It was time for a real solution.

That's when I stumbled upon Motorcycle Michael's solution. It not only makes sense, it works.

The culprit are two bad connectors on the LG display itself. Disconnecting, cleaning, and reseating the two connectors instantly solved the issue and I've been running 100% brightness for two weeks 16+hours a day (I work from home).

Here's a recap of Motorcycle Michael's solution:

1. Open the case and very carefully disconnect the four connectors from the back of the screen. Here's a great tutorial to walk you through the process: https://youtu.be/xfP9mRlwYFI (only the first 3 minutes apply).
2. Place the screen face down on a soft surface such as a bath towel.
3. Locate the two ribbon cables on the back of the screen that extend from the middle of the screen, to the edge, then to two of the corners.
4. At each of the two corners, carefully peal back the silver metallic tape to expose a cloth tape, which you need to peal back. This will expose the ribbon cable and connector.
5. The connector is held in the socket by a white plastic retainer clip. Unfortunately, the tabs must be broken off to remove the socket. This can be done with a screwdriver or long-nose pliers. This step is irreversible.
6. Remove the plug. Insert and remove the plug several times to "clean" the metal contacts.
   PLEASE NOTE: If you use contact cleaner, DO NOT spray into the socket. Only spray the plug. Why? The cleaner will leak into the display and appear on the inside surface of the screen, which creates a blob on the screen - which you will see the next time you power on. Fortunately, the blob will eventually evaporate (1-2 hours) - but it can be frightening until it does.
7. Motorcycle Michael suggested adding a thin plastic wedge to help the plug to maintain contact, or using a dab of silicon dielectric compound. I did neither of these suggestions, as I felt confident the tape that was pealed back earlier would hold it just fine.
8. Place the tape back over the ribbon cable and reassemble your computer in the opposite order you took it apart.
   SIDE NOTE: Since you already have the case open, consider cleaning the dust buildup around the fans, duct work, and grill along the bottom edge. A can of compressed air would do the trick.

I would like to publicly thank both Motorcycle Michael and pbook4g5 for adding their experience and solution to this discussion. It was pbook4g5 that convinced me that it was the connection on the display itself. If you read his posts, you will see he followed the same replacement procedure prescribed by the Apple Tech Manual (which he owns for this model). pbook4g5 indirectly proved Motorcycle Michael's solution since his replacement screen would have had a newer connector.

If you try this repair and it provided a permanent solution to your black screen problem, please share your success story so others can learn and benefit from this solution.

Lastly, if this repair does not provide a 100% long-term solution for myself, I will provide a follow-up post stating so.

HERE IS THE SOLUTION

The problem is overheating. This usually starts if you have replaced the harddrive. My original harddrive was one of the really cheap Chinese ones that Apple had purchased with a high failure rate. They were crap. I replaced it with a great 2 terrabyte drive. Unfortunately after I replaced it I started having the going to black and shutting down problem. If you have the original harddrive it might be that it is working, but the temperature sensor is no longer working. I'd recommend you replace the harddrive, also. I bought my 2tb drive from ifixit.com. They are a great site. There are youtube videos that will walk you through replacing your harddrive, step-by-step, unless you have a local fixit place. Apple will not replace them with drives they don't sell.

The original harddrive had a temperature sensor that told the fan when to spin to cool everything down. Without that sensor the fan misreads the temperature and shuts the machine down. BTW this constant shutting down and revving back up is not good for your drive.

There are several solutions.

Solution #1: Try a free software program called smcFanControl. Here's the url:

http://www.eidac.de

Solution #2: If that doesn't do the trick you can buy a more robust fan controller for $29.95. Their site also has a complete explanation of what is happening:

http://www.hddfancontrol.com

Solution #3: Go to amazon and search for small desktop fans. Buy a really small one and just put it on your desk behind your MAC and run it to cool down the back of your Mac. That will also work.

It is a heat problem. I'm surprised that the people at Apple don't know this. I find that as long as my iMac is running at 52°C I'm fine. But once it gets to 54°C or more, it starts going to black and shutting down. Then when the fan spins down I can click on my mouse and it'll start back up and I'll be find for a while.

Like many of you, I took my iMac into the Apple store also and they couldn't replicate the problem because the store is airconditioned and the machines don't often get above 54°C. So they aren't going to shut down.

I hope this finally solves the problem for you guys. I know I was extremely frustrated. If it doesn't solve the problem don't hesitate to contact me at yvettegr@me.com.

Good luck. -- Yvette

Here's an update on mine.

I drove 50 minutes to the Genius Bar today and, of course, it would not do the montior shutting off trick while I was in the store and it had been doing it (this very morning) to the point that it was nearly impossible to use. I get to the store and nada. Go figure.

Anyways... the genius gave me a course of actions to try to narrow it down as to the cause and eliminate some possibilities.

First, try making a new user account. If it quits doing the blacking out while using the second account, then it's something tied into the first account.

IF it continues to black out after making a new account, he suggested I reinstall Lion (not wiping the drive, just over existing install and this should leave all my personal settings alone)

If that does not work, he suggested I go into the disk utilities and wipe the drive then do a fresh install of Lion. If I restore anything from a backup to only get non-App files such as docs, pics, music. Manually reinstall all my apps.

And if it STILL continues to do, bring it back into the bar and leave it with them. It could take 1 to 2 weeks to diagnose and fix.

I got home, set the Mac backup and BAM, the screen was blacking out! Why couldn't it have done that at the Apple store?

I'm trying the new user now, I'll keep you posted as to the success on it.

Here's an update on my Mac.

I made the new user account ( which was a pain setting everything back up the way I like it) and the problem disappeared for a couple of days. BUT it came back! I haven't had a lot of time, due my in-laws health issues, so that was as far as I've gotten and have just been dealing with random screen shut offs.

Last night, the screen was shutting off right and left. So I had the inspiration to check to see if the LCD was still on and maybe the backlight was the problem. Turns out thats my problem.

To check this you need a fairly darkened room. Take a bright flashlight/torch and hold it by the darkened screen at approximately a 45 degree angle to the surface ( it might take a little fiddling with the angle to find what works for you). IF the LCD is still on, you should be able to see open programs or whatever you were running through the glass. I set up a browser window that had lots of white on it, like this site. Then I could command W to close the window and watch it happen to be sure I was seeing what I thought I was seeing.

So now I have to get it in again so this can be repaired. Which will be hard to do with a tight schedule.

Hope this helps.

I had this problem also. My hard drive stopped working because of all the sudden stops without properly parking the drive. I had to reformat it, but couldn't get the operating system to load. The fine Apple Geniuses were able to load a system. I took it home and it immediately started going to black again.

I did massive research on the web and solved the problem, and came up with a reason for the problem.

The cause is heat. The SMC fan is not cooling down the system which is then shutting down because of the heat.

There is a temperature sensor in the drive to supposedly prevent this. However, if you've changed your drive like I did, and replaced it with a drive that did not have a temperature sensor, thent he fan controll gets all confused, doesn't turn on properly, everything heats up and then shuts down.

This also happens on factory installed drives when the temperature sensor goes bust. A lot of Apple's early drives for iMacs and MacBooks were really cheap and the sensor failed. I had to replace my factory isntalled drive because it failed. (Thank you time machine).

The solution is a simple FREE software download called SMCfancontroller that turns your fan on at specific RPMs, and turns it off when you aren't overheating. I installed the software and haven't had a "go to black" moment since. The software can be downloaded here: http://www.macupdate.com/app/mac/23049/smcfancontrol

There is also another fan controller called Ultrafan which is also free.

There is a paid fan controller, but you don't need it. the free ones work exactly the same. The paid fan controller gives you a 1 HOUR DEMO, which is not enough to evaluate whether or not it works.

BTW if you drive has failed and you have a time machine backup, which backed up before upgrading to Mountain Lion, DO NOT UPGRADE TO MOUNTAIN LION until AFTER you've restored your time machine backup. Install Lion first, do your time machine restore and then install Mountain Lion.

I found out the hard way that Lion time machine backups are not recognized by Mountain Lion.

Hope all this helps.

ricardoh123,

If you still have the warranty... use it!!! I did. It saved me a lot of money!!! Roughly $1000.00!!!

OK. If you have an iPhone/iPad, record the issue, try to replicate it again and then show it to them! It's way better than explaining what the **** is going on. A recorded video is considered a documentation. (This is a continuation from my 1st post above) During my 2nd appointment, I've tried everything to replicate my issue and... No issues. They did another diagnostic, passed with flying colors, and I picked it up the next day.

I hooked up everything at home and then after an hour or 2, the same thing happened?!? My screen went blank with the music/email notification sound/volume going up or down still sounding off. I recorded everything on my iPad from turning it OFF to ON to doing the normal stuff I typically do. In this case, watching Youtube. I was unfortunate yet, fortunate to replicate while recording it on my iPad because it happened again and again.

Long story short I visted the genius bar a total of 9 times to resolve this issue!!! I complained about it & it went all the way to corporate customer relations.

Long story SHORTER, they replaced my video card, the mother board, & the monitor. My computer is working fine. No more blank screen with sound.

So the only issue (which happened 2 times so far but it's not a huge issue) is... I get these different color prints on my screen & then it freezes. The best way to describe these prints is like... removing a adhesive tape from a screen but the adhesive is still on the screen. I don't know but that is it.

So use your warranty & record all issues!!!!

Well I'll add my two cents here since I'm also dealing with this same issue (27" iMac 2.66 i5 Late 2009). A couple of months ago, my machine turned itself off (or so I thought it did). In reality, just the screen went off, so I restarted and it came back. Fine for a couple of months. Then I thought... hey, I should research why it did that...

That's when I found these threads. And literally, almost as soon as I clicked on one, the screen went dead again. iTunes was still playing, and I was still getting external video to my secondary monitor. I read somewhere asking if I could see a faint image on screen by holding a light to the lcd at an angle... yep, image was there. So, I confirmed the backlight had gone off.

So I did some searching. My machine started going dark every few minutes (and the machine wasn't warm at all... it was cold). Sometimes a PRAM zap fixed it for a few days, but eventually it got to the point where there backlight was shutting off a few seconds after startup.

After reading EVERYTHING in this thread, and tens of others, I thought the first logical step was to replace the LED Driver board. Found a seller on eBay selling new, OEM Apple boards for $52. I bought one. Installed it. The old board did have some slight discoloring on the soders near the power connectors, like they were slightly cooked... I thought that was interesting.

Machine ran fantastic for about three weeks. Zero issues. Well, the issue is back again. I've got a thirty day return policy with this part so I inquired about another one.

In the meantime, I thought the next logical step was to replace the LCD panel since the LED backlight is integrated with it. So, I ordered a used panel for $100 (I stole it using eBay's make an offer option). I ended up getting it from the same seller of my backlight board. So, he shipped them out together. They should be here Wednesday.

From everything I've read, you replace the LED driver board first, and if that doesn't fix the issue, replace the LCD panel.

IF that doesn't fix the issue, then I think my next step will be the power supply itself, since thats what's driving the LED driver board. Hopefully I don't need to do that, though. I'll keep everyone updated. Such an annoying issue.

*My fallback is to just buy a nice(r) external display and mirror them and use the imac as an overgrown computer with a dead LCD.

I responded earlier about a free fan controller. However, I've since found that springing the 29.99 for the paid HDD fan control solved the problem for me.

The problem is that your iMac is either heating up, or thinks it is heating up. When that happens the iMac shuts down. My problem started after I replaced a defective hard drive. The hard drives that come with iMacs have a built in heat sensor. When you replace your hard drive the machine doesn't regulat the heat properly. And sometimes the heat sensor just breaks.

The HDD Fan Controller solves this problem completely. Ever since installing it a while ago my iMac has not gone to black once.

You can purchase the HDD fan controller at: http://www.hddfancontrol.com

They have an indepth explanation on what is happening to cause your iMac to shut down.