iMac screen goes black, but system runs fine in background

Update on my previous post Having concluded that this is not a hardware problem I too installed the TG pro software and set the fan to 10%. I also went into system Preferences and turned off energy saver also turned off screen saver. My screen is set at 100% brightness and I haven't changed it what I did do is go into accessibility and changed the settings there as displayed below. Now this hasn't fixed it completely but it is far more stables ie I'm getting around 6 hrs usage before it goes black to bring it back up again I just fiddle with the display settings and then reset to what's shown below. Not the ideal solution I know but at least I can get my work done ( Thank goodness for the second screen) I have noticed a few other odd things with this problem such as I don't always get asked for my password when I log in it just goes straight to my desktop. setting the Mac not to change the background image is ignored the image still changes. I lost all the extra desktops I setup. although I have upgraded to the latest OS I'm seriously considering wiping the drive and doing a completely fresh install. The main problem with such a drastic measure is the time it will take.

Don't know if it makes much difference at all but the Fan Controller I use is called HDD Fan Control.

I've messed about with various settings to increase speed etc but this made no difference which convinced me that it was not a cooling issue. Also, by "increasing" screen brightness to 100% alleviated the problem (for a while). These things together seemed to defy any suggestion that it was a cooling issue. Since my OS upgrade on the 12th April I haven't encountered a single black out. Long may this continue. Just to follow suit I've attached a screen shot of the HDD Fan setup.

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I recently ran into the same problem with my iMac (27-inch, Mid 2010) 2.8 GHz Intel Core i5 ATI Radeon HD 5750 1024 MB computer w/ 16 GB of ram. The screen started flickering than blacking out all together shortly after updating from El Capitan to Sierra. I called Apple and the technician basically told me there was no know issues with upgrading to Sierra. I tried Resetting Vram, Pram, using a different keyboard, booting in safe mode, etc. Nothing worked.

In the end resetting the computer back to El Capitan was the solution. No issues experienced since reverting using "Command-R" during start-up. Instructions available by following the link here: How to reinstall macOS - Apple Support

They do not offer hardware support for this iMac any longer, so I was glad to get back to having a monitor that functioned normally. A couple of years ago I had the power supply replaced, but have had few other issues with it since. Best of luck to those experiencing the same issue.

Hi,

I tend to agree with sureguru, but sadly after being in an apple center for 2 times with no success (they didn't had the issue) and after trying all the possible solution posted here and on other forums, I ended buying an external monitor (Dell UltraSharp U2312HM).

This just to let you know it's a viable solution, not the best, but viable.

So, i've been dealing with this issue for awhile with an older (2011) 27" iMac that i use as a second monito

A couple of weeks ago i finally scheduled an appointment at the Genius Bar. .. It turns out its a video card issue.

I think i paid $150-ish and it was ready in a few hours. Problem fixed.

Late 2009 iMac 27". SOLUTION: I'm reverting back to Snow Leopard.

History: The black screen happened when I first opened my iMac back in December 2009. After six months and many complaints by thousands of iMac users, Apple finally released a firmware update that fixed the issue. My iMac worked great until I upgraded to Yosemite a year or two ago (ugh, and I knew I shouldn't have done it!!!). The black screen was sporadic at first and progressively got worse. After the latest El Capitan update. I can't get the screen to stay on for more than a second now.

This morning, I booted up Snow Leopard from my external HD.
Viola! No more black screen. So it appears to be another firmware issue, just like the one Apple had all the way back in 2010, but now it's happening with the newer operating systems. I hope Apple fixes it. I really don't want to go back to Windows and PCs. I definitely prefer Apple products overall.

I don't believe all of these are heat issues as mine will do it from stone cold. I tried altering the brightness and the problem went away. YAY! 5 weeks later . . . it's back and altering the screen brightness has no effect. I've done a clean out (not a lot of dust though), I also have an aftermarket fan speed controller set at higher speed and accelerating sooner. Looking for a new idea now.

Just Wondered has anyone else has their mac setup with duel boot into windows? When I run from windows I don't get the black screen So this tells me It is not hardware related ie it's not over-heating, or keyboard or loose cables or backlight etc but a software glitch in the mac os. I can run all day in windows but when running on Mac platform I'm lucky if the black screen only comes up a dozen times in a day's work. Thank goodness I have a second screen. I'm running a late 2009 27" i5 with 1 Tb SSD and 32GB Memory. No problems when I run in Windows 10 only in Sierra

I'm still running El Capitan.

I might update to Sierra and see if it helps. Have been reluctant to as I'm still using the original 4GB RAM and wasn't sure if it would turn my machine into a brick in mud. 😕

MY problem started sometime after I installed Sierra on my mid-2010 27" iMac. It's usually after working for 4 hours. Keeping the brightness below 1/2 helps. I will try the TG pro software and turning off automaitic brightness. It has to be software or sensor related.

Very interesting. Mine is also a mid 2010 iMac 27" and yet my issue seems (so far) to have gone when I upgraded to Sierra. Been about a week now without a black screen but too soon to consider it an absolute solution. As expected, a noticeable sluggishness has resulted from the upgrade. Time I upgraded the RAM I think.

I Don't have a display settings that looks like that; maybe you aren't using the same model iMac.

I Installed trial version of TGPro and was able to work for three days with higher brightness, all the way to 100%. But now this morning it's going black again after about an hour of work. Fan is not running, temperature is well below normal. This is very annoying and is costing me time and money!

I will call Apple again.

Hi, Michael, the settings I showed are found under Accessibility in system preferences then click on display in the left-hand panel. I haven't done a complete rebuild yet but I have reinstalled sierra again manually and I have not had a black screen for 5 days I didn't touch any of my other settings that I mentioned in the previous post and have been doing some fairly heavy video and audio work for up to 8hrs at a session and all seems to be working.

Thanks Gomoweb. I should have just reread your post more carefully.

I got rid of TGPro as it didn't seem to help. The tech person at Apple Support is blaming the video card. I have an appointment at Apple store on 4/27; I'll let you know what they say.