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This solution covers for Nokia 6700 classic Backlight LED not working on the LCD Lcd display that result to a dark or black Lcd LCD display.
You may first try to install a new LCD Lcd module before applying or using this solution below.If the LCD Lcd is already tried installing a new one but still the backlight LED still not working or unable to light up. You may then need to trace, check and or replace the components showed on the solution above.
There is a BVAT voltage line that supplies to the LED driver IC and you can check this voltage about 3.7 volts which is came from the battery  positive terminal. and came way across to the two filter coils before it feeds in to the LED driver IC.

If the the voltage supply line is okay, remove the LED driver IC and trace each corresponding solder ball terminal line paths through to the pin connector and VBAT voltage line filter coils.
Rework and clean the solder ball terminal pads.
Replace the LED driver chip if the problem unsolved.

Heres a step by step procedure on how to fix or repair a damaged nokia 6700 slide that has a navigation key and upper keys that stop working or not responding when being pressed. This solution may also help work if the device show charging indication but unable to turned  the Power ON.
If encountered this problem the solution below will tell us which particular parts or components that might damaged and caused the problem.

In Nokia 6700 slide the upper keys like the soft left, soft right, up, down, select, right, left, send, menu, S60 and the power ON OFF key is mounted or connected on a flexible cable wire.
This solution below shows the upper keys connection with each other  keys.

Aside from keypad button connection, there also other major operational circuit is being connected to it like the LCD display, microphone, earpiece and camera.
Once the flexible cable wire damaged or breakdown all of these connected circuit will show some difficulty and problem.

In troubleshooting  the upper keypad problem, you must first ensure to check the flex cable wire or try to install a new replacement spare if having trouble how to determine if it is already damaged or not.
A damaged flex can be checked visually for looking some cuts or brushes but sometimes not so easy to determine.
Now if the flex cable wire is already been replaced but still does not solved and fix the problem, you can proceed  and see this soltion below for further troubleshooting.

Now, this solution shows the location of the two ESD-EMI filter used on nokia 6700 slide keypad circuit.
This filter ICs also holds the numeric keys, if one or both of these keypad filter IC is damaged this will result to keypad not responding problem.
By replacing this keypad filter ICs will possibly help fix and solved Nokia 6700 slide keypad malfunction problem.