iMac randomly goes BLACK - started after OS upgrade to Sierra 10.12.3

[honestone]

By the way, JamesD, in case you do get Yosemite, yesterday Apple released a Security update for it:

http://tidbits.com/article/17139

That update will not be on the thumb drive you might purchase from MacInstaller.

 

[MystressMac]

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I have a late 2009 27" iMac.

Flawless until last weeks OS upgrade to Sierra 10.12.3

First problem was random freezing (cursor would move on screen but no mouse click function)
I disabled WebGL. Voila! Robust fix, freezing problem never heard from again

BUT NOW!...

Randomly the screen goes black.

- if, say, a YouTube video was playing, you can still HEAR it, so the “computer” is still working, just no screen

- if you were typing in a document and kept typing, the text is there when you get the screen back, so again, “computer” maintained, it was just the monitor went black

You can “get the screen back” by

- a reboot

- sleep the system then wake it (opt-com-eject, space bar)

- sleep the monitor then wake it (shift-cntrl-eject, space bar)

But the effects are only temporary.

Monitor will black out again sooner or later (may be 2 hours, may be 2 minutes, may be 2 seconds!!!)


- I have reset the PRAM/NVRAM numerous times.

- I have reset the SMC numerous times.

- In Energy Saver I have set my Display Sleep and Computer Sleep times to “Never”.

- The fan speeds and temps are nominal, so it’s not a heat problem.


I have done countless web searches, can’t find any real solution.
Everybody just says reset the PRAM/NVRAM and SMC.


But many of the posts/replies I've found are older.

So I thought I’d post my own thread and get some NEW EYEBALLS on my problem.


Any help greatly appreciated.

James

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James:

I think it's likely that your problem is a faulty LCD (Liquid Crystal Display)

Here's why:

I had the same problem. (screen intermittently goes black. If playing a video when this happened could still hear audio but could see no video) Tried the PRAM reset to no avail.

I took it into the Apple store, they tweaked some software and ran it through a stress test but could not replicate the black screen problem.

Within 3 days of getting the iMac back from this Apple Store "repair" the black screen problem returned.

I took the iMac back to the Apple store where they changed the vid card and something else (sorry can't recall what) but when they powered machine back up they saw the black screen problem was still there. The tech told me he shined a flashlight on the screen and could see the video playing and could hear the audio and that this indicated to him that the culprit was a "bulb" which is part of the LCD (Liquid Crystal Display). So, they replaced the LCD and now the machine is working great and there's no recurring black screen.

Hope this helps!