late 2011 IMac 27" random black screen - GPU or other how do i prove?

[decotopian]

Hi All,

I have inherited a 27" Imac late 2011. IT was given to us because the screen keeps going black after a while and it wont come back on, the mac is clearly running in the background, lights are on on the mouse, mouse clicks make noises etc.

I have done some research and have found that its a common problem that the graphics processor solder gets cracked and needs reballing.....

But - I need to prove this before I go down this course of action to have a hardware repair.

One thing that doesn't add up for me is that if I press and hold the power button to reboot the machine will come back on - even if just a few seconds after it has gone to screen black mode. So that tells me that it may not be hardware?

What I have done to troubleshoot so far....
1. New OS install High Sierra
2. Used a fan speed App to put all CPU / HDD and DVD fans on max to see if heat was the problem - all temps hanging around 49 degrees max.
3. have looked for WHEN it seems to fail and go to black screen. It seems not to do it while the machine is in use - arguably i haven't used it for hours and hours but i think the evidence is pretty reliable. It seems to do it when you leave it for 5- 10 minutes. Is this a default sleep mode duration or something like that?

What else can I fiddle with to try and get to the bottom of this - are there any logs / error codes I can check or parameters I can change to find out what is going on before I have to spend money???

PS I am a PC convert and used to work in 3rd line PC support, Mac troubleshooting skills still bit fresh but learning fast!

 

[MacInWin]

Sounds like it isn't waking up from screen saving. Try going to System Preferences/Energy Saving and sliding the sliders for the display all the way to "Never." What that will do is keep the screen lit forever, never letting it go into screensaver mode. If that solves the problem, you have a couple of choices--leave it there and just put up with the screen being on all the time or look for a reason it's hanging up in screensaver mode. If it doesn't solve the problem that points to a hardware issue being more likely.

 

[decotopian]

Hi MacInWin

I did this and yep sure enough so far so good, it will go to Screen Saver but will come back up. The thing is that it has had a total new OS install and we haven't yet put software on it - so basically its completely clean.
. It was sold to us with the fault of the screen going blank..... I wonder what it could be?

 

[MacInWin]

Well if you do a search on the subject of "mac screen black on wakeup" you get lots of hits. Here is one article: http://osxdaily.com/2017/04/02/fix-black-screen-wake-sleep-mac/ that suggests an SMC and NVRAM reset, but if the previous owner knew about it, they may well have already tried that.