If the earpiece is not working or no sounds can be heard on it, you may first manually check the receiver speaker using a multimeter. If the speaker is damaged replace it. A poor,distorted or garbled sounds is also an indication of a bad speaker.
If the speaker is okay clean the speaker terminal contact pads, ensure that it has properly or good connection between the speaker’s terminal. Check the filter components, such coils and ESD diodes.
Samung S5620, S5628 Ear Speaker Ways,Track, Jumper, Solution, Repair
Samung Gt-S5620, S5628 Earpiece Speaker Solution