Hi,
As I understand you have a problem with the ringer (buzzer).
Open this manual:
[guide|51579]
than go on step 3, the second picture.
The buzzer is on the rear bezel (down left). There are not a direct contact between the buzzer and the main board.
Now see at the display assembly (same picture - down right). There is one yellow flex cable stucked on the display assembly. This cable makes connection between MB and buzzer. Check this cable, also check the small gold pins on the main board, near to the buzzer.