Microphone faulty after replacement

Hello All,

I have replaced a couple of my friends iphone 4 microphon/charge port assembly and afterwards the microphones havent worked, i have tried 5 different mic/port modules so it is unlikely to be those and on one the mic i replaced wasnt faulty and when i put it back in it works again. The microphones work on facetime but not for phone calls. I have also restored the 2 devices from genuine apple firmware stock and the latest version. Has anyone got any ideas as its confusing the h&*l out of me. Thanks All.