Philips 55PUS6704/12 broken backlight or PSU?

I have a Philips 55PUS6704/12 that's maybe 3-4 years old now (out of warranty). When i turn it on the ambientlight comes on and the Philips logo flashes really quickly the just a black screen. If i shine a flashlight on it i can see the menus and stuff like that.

I've taken of the back and measured the voltage at - VLED (5.34v) and + VLED (25.5v) measure against ground.

How can i find out if it is the board that need's to be replaced or the LEDs?