Here's the repair guide solution to repair Nokia 5730 xpressmusic LCD LED backlight problem, a failure when the LED backlight failed to light up that result and turns the display into a dark, black or blank screen display.
This solution may only work and can be applied if the LCD and flex cable is properly check, test or by way of replacing it already but the problem still exists.
You may check the filter coil first, then trace the line paths on it.
You may also then remove the LED driver IC and trace all corresponding lines from the chips ball bumps through to the flex cable pin connector, which is in pin number 47 and pin number 50.
Just follow the picture guide above to determine each of its line being connected. Replace the LED Driver SMD IC if all line paths are working fine.