Chosen Solution

Hi I use ifixit so much and always find my answers here but now I’m stuck. I’ve got an 27 inch core2duo late 2009. After booting the screen turns black (so I see the apple logo and then the screen turns black, the machine stays on and I hear the HDD). I tried the LCD on a different iMac also late 2009 and then I got it booted but after a few seconds it turned black again but you hear the HDD run. I exchanged the LVDS cables and they both do the same. I know the LCD issn’t completely broken because it sometimes works… Question is: whats causing the LCD to turn black after a few seconds? Update (06/08/2015)

Dan included is a screenshot os temperature gauge pro. I kept on googling and I think there is something wrong with the led strip on my LCD or the board steering it. kind regard Frederik

Can you aim a flash light at your screen at a low angle you should see your desktop icons. If you can you know the displays backlight system is failing. You can also try plugging in an external monitor as well to see if the desktop is visabable on it. The next issue here is why is the display winking out. You may want to download this app: temperature gauge pro it will allow you to monitor the internal thermal sensors. What you want to check out is the LCD display sensor. Post a screen shot for us to see.

Several days ago it started happening to me. I read everything I could find … one thread was 17 pages long. The best I could do was run it at 20% brightness. If I got bold and tried to nudge it a bit higher … … But, just as a wild guess and maybe in frustration I jammed (in one nanosecond) that !&^#% screen brightness slider (not the brightness button on the keyboard) to full 100% brightness. And nothing happened! It stayed on, and that was several days ago. The next day I tentatively lowered it to about 80% (where it had been set for a couple of years) … and all is well so far. Try it. Nothing to lose. Ron in SW Alberta

Exact same problem, which happened after a HDD replacement to SSD on a late 2009 iMac. I salvaged the circuit board from the old drive to keep the HDD temp sensor in the circuit to control the fan speed.  The display blackout started almost immediately after replacement.  I replaced the LCD temp sensor but to no avail. I wonder if the apple built-in diagnostic process looks for a delta between the various temp sensors and shuts down the display if there is too wide a disparity between them? Thinking of trying the inline digital thermal sensor cable from OWC.