I've been looking for a couple of weeks now how to solve the problem with both the microphones not working on my Xperia U st25i.
After trying everything I've read about this topic (disabling the live wallpapers, Live Manager, soft reset, repair with PCCompanion, etc) I haven't been able to find a solution. So I ask a friend of mine, that has the same model, if I could disassembly his phone and try to connect the bottom part (where the primary microphone is allocated) to my phone to see if at least my primary mic would work. When I was at the point of disassembling the bottom part of his phone I saw that the ribbon connected to the phone could break so I decided not to go any further. So I reassembled his phone and the result was that now his primary mic isn't working. So now I have one phone with both microphones not working and another one with the primary microphone not working.
Anyone knows what could I have done disassembling my friend's phone to break the primary microphone?