Here's the Nokia C3-01 solution for keypad filter IC. You can use this solution if having or already tried replacing the NUMERIC Keypad membrane flex board, or already tried replacing the said filter IC but the problem still exists.
This solution may works if having trouble finding the cut-off or open line paths of the keypad connections especially for wet or water damaged Nokia C3-01 touch and phone.
The solution below shows the connection line paths of the keypad filter IC that can be use for quick tracing the corresponding keypad connection line paths down to the keypad pin connector.
The keypad filter IC is mounted or located besides the battery connector. Just trace each corresponding solder ball bumps connection, for a deep tracing repair procedures.