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

Well, as soon as I moved that brightness level the screen went black. I re-booted the computer again and it came to life with the brightness defaulting to 25%.

Back to Square One. I wonder why my little fix worked for an hour last night.?

Je me demande, "Qu'est qui se passe?"

@Boomer49: it didn't. Our brains are build for detecting connections, so if an action is followed by an effect we quickly conclude that the effect was caused by the action. But often this isn't the case. That's why in Science you need at least three repeats before you trust a result, and even then others have to confirm it independently before it is accepted.

Btw a LOT of superstitions arise from these false connections .

Hmmmm .... just tried bumping the brightness from 25% to 35% three times and it blacked out immediately so I tried something I maybe read about yesterday ... I just jammed that effen slider to 100% as fast as possible ... and the screen is holding at 100% right now.

Go big or go home. Let's see how long it works. It is now 1:35 on November 15th, 2015.

It is 7:25 and heat is (as always) pouring out of the top of the iMac (as it has since I bought it a few years ago) ... the screen (at 100% brightness) gives-off the usual infrared warmth in this cool room ... BUT IT IS ALL STILL WORKING.

Please just do what I did, and give feedback to this website.

Here's what worked, at least for a day .... Before it goes black after nudging-up the brightness-control from 25% to some lame 45% on the Systems "Display" app ... doomed to fail ... be ready to just crank that ****** slider to the max 100 in a nano-second. Don't use the keyboard brightness keys.

A day in ... and so far all is well ... the heat is pouring out of the top vents at the back of the screen (as it has for a few years) but ... so far so good.

Them Apple engineers are not earning their keep. They maybe don't follow this **** on the Internet?

There's no budget for catastrophic Apple failures like this?

R

I took Psych 100 in 1967, and know that "correlation" does not mean "causality" ...

But thanks for chiming-in ... everything helps.

Four days and still working fine! As I posted on another thread ...

Several days ago it started happening to me. I read everything I could find ... one thread was 17 pages long. The best I could do was run it at 20% brightness. If I got bold and tried to nudge it a bit higher ... <POOF> ...

But, just as a wild guess and maybe in frustration I jammed (in one blazing nanosecond) that *!&*^#% screen brightness slider (in the Display section of the System Preferences App ... not the brightness button on the keyboard) to full 100% brightness. And nothing happened! It stayed on, and that was several days ago. The next day I tentatively lowered it to about 80% (where it had been set for a couple of years) ... and all is well so far. Try it. Nothing to lose.

My iMac (27-inch, Late 2012) is also having the same problem: after entering into sleep mode with the default settings of the Energy Saver the screen goes black and stops responding to the keyboard, mouse, and the power button.

The only way to make it work again is to do a SMC reset by unplugging the power cord, wait for several minutes, plug the power cord, wait for more than 5 seconds, then pressing the power button.

When did it start? About a week after updating El Capitan to 10.11.1.

I have tried practically all the suggested procedures I could find in this support forum with no results. The only thing that seems to work is to shutdown the computer when I am not using it AND unplugging it from the wall. I also have observed that the longer the iMac is left unplugged, the longer it seems to go until the next time the screen goes black.

Now I am trying the suggestion from Boomer49 above.

Hey Tabrings,

I've got my fingers crossed ... it would be great to know if I have been able to help someone.

It wouldn't exactly be solving the mystery, but a fix is better than nothing. 🙂

And if it doesn't work after a couple of tries, try minor tweaks and variations. Be sure to let us know how things work out.

Boomer

Thanks, Boomer49. I set the brightness level at 100% following your procedure, and my Late-2012 iMac has been working well for 4 hours so far. I have set the Energy Saver to put the Display to sleep after 30 minutes of inactivity. Let's see if it comes back after going to sleep.

Yahoo!!!!!

Worth noting .... just to be on the safe side, I set the Go to Sleep schedule to NEVER. A minor but cautious idea. To heck with anything like defaulting to SLEEP. And, to sort of "allow" for that, I set the screen saver to the least energy-intensive possibility ... one single slowly-squirming coloured wormlike line writhing around on a black background.

To **** with energy conservation ... I drive a 2001 Hyundai Accent ... very low carbon footprint. 🙂

Soooo happy to hear about your results.

My iMac 27 (late 2012) just shutdown while I was in the middle of writing an email.

Screen brightness was at 100% and Energy Saver was set to never go to sleep.

Console Log says that:

11/21/15 8:28:17.000 PM kernel[0]: Previous shutdown cause: 0

Cause #0, according to other posts means loss of power.

Tabrings,

Well, that was disappointing news ... just when we thought that you were "on the road again" ....

May I suggest that you once again do the old "slam it to 100% brightness as fast as possible" trick ... and then, if it's still OK after a few minutes, smoothly lower it back to about 80%. That would exactly duplicate my procedure, which seems to be still working for now.

And 80% is just fine for most situations.

Tabrings,

Well, that was disappointing news ... just when we thought that you were "on the road again" ....

May I suggest that you once again do the old "slam it to 100% brightness as fast as possible" trick ... and then, if it's still OK after a few minutes, smoothly lower it back to about 80%. That would exactly duplicate my procedure, which seems to be still working for now.

And 80% is just fine for most situations.

Tabrings,

???????????????????????????????????????

You owe us a ******* reply.

Maybe Buddy has shuffled-off this mortal coil. Has anybody else tried this "fix"?

FFS, I am still here.

And craving some feedback ...

Ron

The display brightness is not related to the problem in my iMac. I tried various display brightness levels and my iMac would continue to randomly blackout. After a blackout, the only way to restart the iMac was with a SMC reset.

After one of the blackouts I re-started the iMac holding down the D key in the keyboard to boot into Apple Diagnostics. The quick test did not find any problems, but when I selected the extended test, it seemed stuck at 34 minutes during the pass 1 of the memory check, even though it was running for more than 2 hours. I tried stopping the test but it did not respond to the mouse or keyboard. As it did not respond to the power on button, I pulled the plug.

I pulled out the 8 GB memory upgrade I had installed about 2 years ago and left only the original 8 GB from Apple. I rebooted into Apple Diagnostics again and this time the extended test completed in less than one hour and found no errors.

It seems that the problem was caused by bad memory. Now, with only the original memory that came with the iMac, it has been working without any problems for more than 2 days. The screen brightness is set to automatically adjust, and the computer sleep and display sleep have been working as expected.