Here's the solution for Nokia 5630 Xpressmusic with a not working mouthpiece microphone problem. This solution provides some hints on how to fix this problem.
Since in Nokia 5630 used a digital microphone and operated some sort of digital clock to make it work, you may try to restore, flash or update the device firmware first. Refer to the solution below and locate the components holds for the microphone circuit. Then proceed to hardware repair after ensuring that the problem is not a software related.
You may first trace and check the mic supply voltage (VDigimic) from the power IC (GAZOO). Then replace the digital microphone if the voltage line paths is working okay. Just apply a tiny wire if the line pathsis open or cut.