mid-2011 iMac, screen randomly goes dark

[ChrisA]

As the title says the screen goes black randomly. This happens a few times every day then not for three days and then four times in one hour. It might be heat related.

I figured out I can 100% get the screen to come back if I breifly click the power button twice. I do a "click" on the rear power button, wait 4 seconds then a second click. Maybe the first click puts the iMac to sleep then the second wakes it? I don't know why but this fixes the problem. The screen comes back and there is no log-in required and I am back at the desktop. Of course two "long presses" fixes this too by power cycling but this is not needed, two short click works.

The iMac does not sleep when the screen is black as I notice I can still type and when I do the double click on the rear power button I can see what I blindly typed.

Is the above information enough to dianose this? My guess is a failing GPU card.


Anyone know what is wrong? My 2011 vintage computer is about due for replacment but I want to wait until after the Arm-based macs are out. I do have two other computers I can use so I can holdout. But, I'd like to fix this problem if I can. The 2011, with 24GB RAM and SSD boot drive is still fast enough for most normal use.

 

[USB3foriMac]

Sounds more like a backlight issue, not really like a GPU problem.
I'd try to disconnect and reconnect the screen. Particularly the connector to the backlight is sometimes a bit loose. I had one where I took the pins out of the connector, tightened them, and put them back.

 

[ChrisA]

Sounds more like a backlight issue, not really like a GPU problem.
I'd try to disconnect and reconnect the screen. Particularly the connector to the backlight is sometimes a bit loose. I had one where I took the pins out of the connector, tightened them, and put them back.

But why do the two clicks on the rear power button always fix the problem?

Als what does a screen with no backlight look like? Can I see an image on it if I use some kind of light??

 

[USB3foriMac]

But why do the two clicks on the rear power button always fix the problem?

I tried just now: when doing this, screen goes black, then comes back. Screen is flickering briefly, which means it is the backlight that is switched off and on. So that supports the thesis that the problem is backlight.

Als what does a screen with no backlight look like? Can I see an image on it if I use some kind of light??

Yes, if you use a torchlight and look at sections with high contrast (e.g. icons), you can identify those.