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

Hi Markus,

You ran into the same issue as me... the frame is glued onto the LCD. You have to pry it off. It looks like it'll hurt, and it does take some force, but it does come off.

Good luck! My new screen is functioning normally (knock on wood). I also replaced my LED Driver board at the same time.

sooooo i have Mid2011 27inch iMac and Ive been experiencing this problem for about 3 months now. I tried all the workarounds, fan control, switchresX, etc. I dont have applecare and I live in a small town in Hawaii and theres no Apple store/Genius Bar.. there is only a little shop that sells/works with apple products.

I finally took it last week and they have been trying to diagnose the problem for a few days. The tech at the store called and said he opened it up and redid the connections blahblahblah he hasnt gotten any blackouts since so i picked it up, paid their diagnostic fee, came home and plugged it in. SAME PROBLEM! Today, i switched the display to a lower resolution and I havent gotten any blackouts yet..kindof annoying dealing with the black bars on both sides of the screen but its been wroking fine.. fingers crossed!

Dang it. Switching to a lower resolution here too "solved" the problem on my 27in 2009 iMac.

What does that mean?

Spoke too soon. Just blacked out on lower resolution. However when it was running for a long period the brightness was reduced, so that might be working better.

Btw I set up the bottom right corner as "put monitor to sleep" so when the screen goes black a quick trip to the bottom right and out again brings it back.

Thank you, man. This worked like a charm for me. I was about to open the iMac to try to clean the fan because I thought that was my heavy smoking habit the source of the problem. But fortunatelly I found your advice, muchas gracias from Spain.

I have the same computer and am having the same trouble now. Just started doing this the past week after running fine for almost 2 years.

I started having issues with mine about 3 months ago. The LCD would flicker a few times and it will dim about 20%. After a couple minutes, it'll go back to full brightness on its own.

It kept doing that on and off, very inconsistently. Last night in the middle of an email, the LCD went black. I thought the machine had shut off, but pushing the power button brought it back to the point I was in so I know is not shuttinb off. Just the LCD went out.

Now I can only have the LCD on for about 5 to 10 minutes before it shuts off again. Luckily, I have a side by side HDMI monitor, and that keeps working fine.

I have an appointment at the bar today, but I am sooooo scared they are going to kill me there as I don't have the care package.

This, just a week after my 2yr old mac mini killed the ethernet port and apple requested $400 to fix it.

My mac mini is now a paper weight. Will my 2011 27" iMac become one as well?

Stay tuned...

Don't worry... just don't let them fix it for you (or it will probably be super costly)

If it was like my issue, it will be either the LED Driver Board (approximately $60 new on ebay and thats the first part I'd replace) or its your LCD display/backlight (I got a used one for $125 on ebay). From there, it could be your power supply or one of the cables or even the logic board, but I bet its either the board or the panel itself.

All semi-easily fixable.

THanks for the info. I am now sitting at the bar and they are monkeying with it.

We'll see what they have to say.

A quick update. Apple Geniuses ended up keeping the iMac overnight for observation. They said that just by me unplugging it, reset the power supply and the LCD driver and it may be enough. (hmmm... I am not sure about that, but OK).

They ended up not being able to replicate the blacking out problem. Just brought it back home and sure enough, the screen is not going black anymore. All giddy and 10 minutes into the working session, it starts flashing and dimming again. This is exactly how everything started 2-3 months ago remember?

I have money that says it will black out again soon. In which case, I know exactly what they are going to say. Let's put in about $600 in new parts. That should fix it! 😢

Is there any update on this???

From what I can gather, the real issue here is the LCD backlight failing?

jjhaffner what happened to your issue?

I took it to apple store and they tested it, on my case the logic board was failing 😢

This can be many different things...
If you're not sure about what is the problem, take it to a apple store (or an authorized store), if possible that doesnt charge for the check of the mac, and they will tell you whats the problem.

Hi all. My problem was easily solved. The old zap the pram actually worked. Been fine for 2 months.

Mine still dims and flashes about twice every hour. Three weeks or so of that game and the whole thing goes black. Power cycling brings it back for another 15-20 minutes and then it shuts off again.

If I unplug it and let it sit for a while, the whole cycle starts over again. Three weeks of flashing and dimming until the screen shuts off.

I really don't feel like spending $600 to repair this junk for now. I'll keep doing the power cycling until it dies for good. Then I'll get something else. You think you spend $2000+ on a machine and it'll be something descent... Nope! 😠

I don't want to jinx a good thing, but my machine miraculously fixed itself.

It has done this before for a few weeks before starting to act up again, however this time it has been good for a few months, so fingers crossed!.

I did adjust the sleep and resolution settings a few times as there was a suggestion this issue may have something to do with the sleep function. Good luck :-)