If ever encountered this problem the solution below will show us of which and what particular components that needs to be check for repair.
This solution may works and can be used if the LED's already been checked by a multimeter and are still working and not already busted or blown out.
Nokia 2710 Keypad backlight LED solution
Th solution above showed the Nokia 2710 LED driver circuit, this circuit holds the LCD and keypad backlights LED's to work. Therefore if this said chip become damaged, may result to LCD and keypad LED's failure or unable to light up.
But if only the keypad keys LED's does not work or light up, you may first check the line paths of the keypads backlight LED's supply voltage.You may start to check the LED first and the keypad membrane flex cable: Then trace the line paths from the keypad pin connector through to a corresponding components where it is being connected.
There are certain components such as the filter coils and resistors on the circuit, you may check this components and replace if found damaged. Just then follow the simple instructions showed on solution above, hope this may help fix and repair Nokia 2710 keypad back light not working problem.