Chosen Solution
I have been having issue of intermittent black screen on my iMac. The screen worked for sometime then started showing gradated screen. The top section being lighter with the bottom being darker. I replaced the LCD display thinking that would solve the problem, but it still has the gradated screen and it freezes up. I opened it back up and checked connections and cleared out the dust on the fans. Now, it’s back to a black screen. I took a picture of the power source while I had the computer open because it looked odd. If someone could tell me if they think the power source is bad or if maybe the inverter is causing the issues, I sure would appreciate it!
A screen which is lighter on one edge than the other implies the backlight circuit is having a problem. Double check your invert cable connections. If that doesn’t fix things then the inverter would be the next thing I would test or replace. This model uses CCFL tubes within the display they can be worn out.
@perna “gradated screen and it freezes up.” is most likely not directly related to the CCFL or the backlight. The issue sounds like it is more related to the power board and video processor which may cause the issues with the backlight. Since it works after you cleaned the fan I’d suggest cleaning all of it and possibly replacing the thermal paste on all the heatsinks etc. Post some images your boards from both sides and of what your screen shows when it shows this again.
