My Panasonic KX-T2315 telephone ringer sound stopped working properly so i decided to resolve this problem. First of all i downloaded the service manual and looking for the faulty component.

Ringer fault is caused by bad capacitor, in this case: “C3″(0.22 µF). I bought a new one and carefully replaced it. If you want to desolder easily the C3 capacitor first you need to remove the grey plastic battery holder element.(it has 2 legs sordered on the board).

After i replaced the bad capacitor the phone started to working porperly.
In this video you can listen the sound of the ringer: