iMac 2009 27" *intermittent display on/off* - Any fix?

[mehvins]

Good evening. I purchased an used iMac (end) 2009 27" and everything worked fine for one month.
One month later, the display would go on and off, but the mac still working. If I tried to move the mouse, nothing happened, but if I push the power button 2-3 times, it comes alive and then shuts down again after a while.
If I keep the display brightness to 2-3%, it works for long times.
Ok, so I've ALREADY searched a lot on this problem, and I've found a lot of forums on ifixit and here, but there isn't really a good solution for this problem.
I replaced the inverter with a new one, it seemed to work, after a while it gave me the same peoblem. So it isn't the inverter. I tried to open, clean it, replace the vsync cable with a new one, I tried to keep the flat cable of the display even better on place with some tape; i tried to remove the LCD prox sensor, I use Macfancontrol and the temperatures are ALL OK even on the GPU....
So what the hell is the problem here!??!?!
it gives me the same problem even in safe mode so it isn't even software related.
The specs are:

ATI Radeon HD 5750 1024 MB
2,8 GHz Intel Core i7
(27-inch, Late 2009)

this problem is making me crazy and there is no fix for it?

 

[Amethyst1]

One month later, the display would go on and off, but the mac still working. If I tried to move the mouse, nothing happened, but if I push the power button 2-3 times, it comes alive and then shuts down again after a while.
If I keep the display brightness to 2-3%, it works for long times.

Does an external monitor also exhibit this behaviour? If so, it could be the GPU.

 

[mehvins]

Does an external monitor also exhibit this behaviour? If so, it could be the GPU.

The same exact problem people got like me tried the external monitor thing and always worked. it's not a gpu problem cause i've played games too, temps are fine, gpu seems fine. I dont have an external monitor to try but i know people who tried on forums it works fine .

 

[rampancy]

Given what you've said, my only thinking is that it's the LCD backlight that's going or gone kaput.

My own searching turned up a Mac 911 article that discussed this issue, but I'm guessing you've already tried cleaning the machine out, or fiddling with the LCD panel's thermal sensor.