Hi,
I have the exact same problem. After the phone is completely assembled, the mic does not work. Once the display is lifted a bit - with the home button cable cable still connected - it works fine. The same moment you put the display on the bottom case the mic is deaf again.
There seems to be a contact somewhere that causes a shortcut or something. Or could it be the little earthing clip mentioned on step 26 of the front panel replacement guide?
See the URL: https://d3nevzfk7ii3be.cloudfront.net/igi/r5pGqAJI6TCa2N3k
Does anyone have an idea? Many thanks in advance
Wolfgang