My Solution

This solution may help fix Nokia 2680 slide On off key malfunction.
Note this solution can be applied if the flex cable is working okay or having tried replacing a new one but the on off key wont work and it shows charging indication on the LCD display when the battery charger is plug-in.

From the keypad pin connector there is a resistor that has a 0 ohms resistance value. You may need to check this resistor if open, replacing it or shorting it may fix the problem