Backlight LCD turns off + Buzzin Noise

Hi there,

my Apple Cinema Display 27" (no more warranty) got some problems with its backlight and I'm not quite sure whether its the logic board or the power supply..

It works for a few minutes, but than it randomly turns down the backlight of the LCD. There is still a picture, that can be seen e.g. at direct sunlight. So the LCD itself should work fine!

I can speed up this more or less random process by in- or decreasing the brightness.

If i disconnect the display from power and reconnect it, it works again for some minutes. Then, same procedure...

There is also a buzzing noise coming from "inside" which gets louder the brighter the LCD is but doesn't really stop when the backlight turned down again.

For me this buzzing noise sounds like a damaged transformer or some other power supply problems... but I'm not sure...

What I'm sure is, that these two problems have the same source and hopefully will have the same solution.

I already tried the things listed in the Apple Technician Guide and the ones on the internet...

What do you think? I thought I'll ask you for some advice befor ordering some parts like new power supply or new logicboard..

Thank you! :-)

Alright guys... I replaced to PSU. Nothing changed..