27' iMac (2011) Screen turns off

Tried all of the tricks listed in discussions group. They all failed.

Installing and running Mac Fan Control and reducing screen brightness gave me a partial break until I had my iMac physically Cleaned by a Mac technician.

PROBLEM SOLVED and my old iMac runs like new

I just recently started having similar issue when iMac screen would turn off for no reason. I would press the hard start button (quick press), wait few seconds, press again(quick press) and some keyboard activity would bring the screen back on right where it was, no re-start actually taking place. I read the posts here and took my iMac apart to check for the listed display connector with possible issue. I noticed however that my issue seems to be time related, screen would turn off after been on for couple seconds. I didn't actually timed it exactly but usually less that a minute or so. This was telling me that overheat could be involved in the issue, either a component going bad after warmed up in the power supply, display driver etc, perhaps a cracked PCB track switching on and off with temperature. Connectors usually don't behave this way. Anyways, took the display out and examined the connectors. I saw no issues, all seems in place, firm as it should be. Following my original thoughts, verified dust buildup on the cooling fans, did some good cleaning and put all together. Working fine after that. It could be:

1)Connector had a contact issue and was resolved with just a little shake

2)Other connectors that you need to take out in order to remove the display had issues and turned good after display reconnected

3)Cleaning the fans fixed the issue, although the dust buildup didn't seem big enough to cause an overheating problem.

Let's see how long it holds.

AAnyone have any ideas with this one?! Already replaced the screen once (2011 iMac 27") this is second screen, computer won't even start anymore, this is as far as it goes then restarts

Update.

Didn't last for too long. Next day the screen started blacking out again.

I took the clear cover and noticed that the display was very, very hot. Decided to take the main board out and do a deep cleaning of all fans and heat exchanges. Some were well clogged. Tested the fans on the bench and all worked fine. Everything put back in place and now running. Time will tell.

Update.

Working flawlessly for 5 days now. Overheating due to limited air flow seems to be the culprit for this issue, at least in my Mac.🙂

Mine has been getting worse the past week. I used to be able to prevent the backlight going off by going to "3 bars" worth of backlight. Anything below that had been safe for years. Now the backlight is going off more frequently regardless of the backlight level.

For almost my entire iMacs life I've run MacsFanControl to keep my system between 35-45c. Anywho, a little story ⚠:

Frustrated with it I decided to open it up and disconnect the backlights vsync cable, someone on Youtube said it helped them. I did that, tested it out and I could not replicate the problem! It was alive again! But after switching off again and reassembling I had that "dark side" backlight problem! Opened it again, put it back together and it magically worked. But the backlight has been going off since!

Thing is... Apple recently increased the price of iMacs here. I was all set to buy a new one this week but they 1) didn't introduce new ones and 2) increased the price of the current/old ones by £400! So no, instead of Apple getting £2k I'm spending it on a new LED driver (or inverter I think they're also called) board from eBay. I don't know if it's going to fix it. If I don't report back assume it worked.

(Thing is this computer is nearly 6 years old now. I installed an SSD, a 3tb HDD, bluray drive, and 16gb of memory into it 4 years ago and it still flies)

Installed a new LED Driver, or backlight inverter, whatever it's called! So far no problems. Considering how bad its been recently I think I've got it sorted now.

Also did a clean with compressed air, bit of WD40 on the fans+DVD moving part bits, polish on plastic+metal pieces. So maybe that helped too.

The replacement LED driver board didn't fix it. So as I was putting my old card back in and boxing up the replacement to ship back, I thought I'd try that technique someone mentioned earlier involving the two wires on the display panel.

I peeled back the metal taped corners where the LED strip wires go into, exposed the connector, removed the white tabs on the sides of the connector by using a pair of tweezers and flicking them down towards the middle of the panel (they come off easy if you do that!). But then I made a mistake! I only had some isopropyl alcohol wipes to hand rather than any real contact or electrical board cleaner. I unplugged the cables and then stuck these wipes into the sockets! I damaged the pins slightly and after some careful surgery I managed to get them back in the right places. I then put the connector back into the socket and put some folded card ontop of them to add pressure - apparently this works. I crossed my fingers and, well, its been 5 days and it hasn't gone off yet! I created an applescript to cycle the backlight from maximum to minimum over and over, because with mine I found that the process of lowering the brightness would cause it to "trip out". I left that running for an hour and it was okay!

So I think that's it for me now. To be honest I don't know what I really did to those connectors. They were really tight in there before I took them out! I mean they're tighter in there now, but I'm surprised that slight difference fixed it. But I'm very happy now! My 2011 27" iMac will live on.

Well it's back! But it's much easier to temporarily fix than before (by turning off the display in OSX or Windows, and waking it back up). I only need to do that once before it works - previously I'd fight with it for a minute or two before it would eventually settle.

I'm going to buy some contact cleaner and give it another go later today. The previous method of reconnecting the backlight wires did help somewhat.

I opened it up again this time armed with contact cleaner and some compressed air to give it a good cleaning. Spent an hour taking pieces (that I could) out and giving them a dusting then a spraying down with the cleaner. Opened up the corners of the display and sprayed the cleaner in the two backlight cable sockets. Put it all back together and oops! The spray leaked into the backlight and created a (cool!) pattern on the display itself! I set the iMacs fans to only come on at high temps and 'cooked' it, causing the excess cleaner to evaporate.

And so far it's great! It still flickers when the display switches back on IF the brightness is set to low. On high there is no flicker. But the fact it remains makes me think the problem will eventually come back. But after 24 hours of pushing it the backlight hasn't gone off yet.

So if you're skimming through;

- Clean out the inside of your iMac!

- Download MacsFanControl and set your fans to use the GPU proxy, hard drive, CPU proxy sensors, all at 40-50 (min-max) degrees celcius.

- Put your display face down on something soft. Follow the backlight cable (the wide cable that splits into two as it sticks to the rear of the display), peel back the metal tape all the way to the corner on each side, slide a screwdriver under the brown cable cover and lift up but leave the black cable underneath where it is. Using tweezers flick off the two white tabs on the side of the now-exposed contact case thing. Then lift the black cable up taking the contact with it. Spray contact cleaner inside, put the cable back in, rinse and repeat a few times. Use a lot if you want but be prepared to wait and hour or so for it to evaporate from the display when it's all wired back up.

-The power supply unit might be causing the display to cut out (I suspect it's part of the problem). You can remove it quite easily and give it a good cleaning if you do! Especially all the unplugged connectors! I recommend WD40's 'fast drying' Contact Cleaner for all this!

-The backlight sync cable CAN be left disconnected, this is the small thin cable on the left. Unplugging it will make the display make a high pitched sound at full brightness and it will flicker occasionally at low brightness. Some people have said leaving this unplugged helped them.

Last update I swear!

So no it's gone back to flickering and switching off randomly. There's nothing else I can do now except fight it when it happens. Whatever I did helped it but I can't work out if it was the pressure pieces on the back of the display, the cleaning I gave it, or something else that got nudged during all this.

Has this issue ever been resolved? I just started recently experiencing all the issues mentioned, originally thought it was the video board and brought into an authorized service center...my thought here.

iMac 5K goes to sleep mode (blank/black screen), the screen will not wake up unless Imac is rebooted

Got this bug just last week awhile after updating to El Capitan......

https://macperformanceguide.com/blog-2016-01.html#20160121_0928-OSX_10_11_3-Slee pBug-iMac5K

Model Name: iMac 27"

Model Identifier: iMac12,2

Processor Name: Intel Core i5

Processor Speed: 2.7 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 8 GB

Boot ROM Version: IM121.0047.B23

SMC Version (system): 1.72f2

Serial Number (system): C02GCEGXDHJP

Hardware UUID: E7A93B22-3482-5D4B-937B-B3EFC7110EFC

Had it dropped off at an Apple Authorized service depot after trying fruitlessly to solve the problem, was sure it was hardware related, backlight, video card etc. The no wake symptom occurred once at service and was fine after that until I got it back home.

The problem then returned repeated just after a few minutes of use and not even completing a reboot to the login, rebooting into internet recovering the screen was stable but that would only allow reinstalling LION. The screen was also stable after several attempts trying to get to recovery mode and reinstall of 10.11.6 which was successful, hoping that had solved the problem.

Currently at at 10.11.6.... unfortunately the problem has returned but so far much less frequently, lowering the brightness with the F1 key caused it twice to go into the black screen requiring a reboot, other than that it has been relatively stable but the bug continues to exist none the less.

Regards

Robert

Dec 1, 2016 9:55 AM in response to rob80b

Problem has just recently gotten worse after being stable, on reboot goes to white screen with chime for a few seconds then black, got to login screen a few times prior to that but now cannot even get it to reset NVRAM or boot into recovery or diagnostics. Using apple wire extended keyboard.

Found a few other comments here but still no definitive solution, quite a few users like myself have had their units into an authorized service center with no success.

http://forums.macrumors.com/threads/imac-screen-goes-black-must-hard-reboot-help .1375427/

https://www.ifixit.com/Answers/View/79159/Random+Black+screen,+Help+please
"I had the same problem and the fix was easy. Download and install the SMC fan control program and bump up the speed on the HD fan. In my case the HD was too hot. I haven't had the issue since."

"I spent under $150 for parts and tools, and ended up successfully replacing the inverter board and power supply. It looked to me as they had been corrupted by moisture and dust."

Dec 1, 2016 10:10 AM in response to rob80b

Given all the related issues I cannot say this an El Capitan issue it just coincidentally started after upgrading.

I was able to login without screen by entering first letter for user then entering password....oddly screen has just come on 20 minutes after going to black at startup?

On a whim turned off automatic brightness just to see...so far so good but it has been less than an hour...

Just a follow up after a trouble free week, Imac has been stable, no further problems since "automatic brightness" was disabled, knock on wood but hopefully (oddly) that was it.

Imac eventually stopped booting, 1/2 a chime and then shut down.

Problem was completely resolved with the replacement of a new back light.

Hey, did you end up finding a solution? I have, or should say had the same issue, but managed to figure out what was causing it.