Samsung Galaxy Alpha SM-G850F Mic very quiet

i have an issue with Galaxy Alpha on microphone. Already changed the whole USB flex cable where the MIC is on it, with even 2 different, new parts, but still is the mic very,very quiet.
This meens, when you speak on it, the other side can hear you only if you screem on it and then is it also still very, very quiet.
i didn’t have something like this so far, so don’t know where to start looking. the phone has no water damage, no other obvious damages on housing or mainboard. all parts look normall.
there is no schematics, no suggestions, there is simply nothing available for this phone modell, so i am asking here for help. maybe some1 had something similar…