Dears,
I want to make sure, that the internal microphone is never used, not even accidently.
Instead, only the headset (3.5 mm) has to be used.
I’ld prefer a solution w/o soldering, but if the only way is physical destruction of the microphone, I’m fine with it.
TIA!
If you also don’t need the webcam you can just pull off the bezzel(yay magnetic) and disconnect the webcam module (microphone is on there), you can even entirely remove the module to save a few gramms if you want.
Alternatively you could carefully tape/cut off just the mic pins on the wecam connector if you still need the camera.
Thanks! Yes, I need the webcam.
Is there any documentation about the webcam module, i.e. which pins are related to the microphone?
(I would try to cover them, so that the microphone could be re-enabled by a potential, future owner of the device. Only if that does not work, I’ld destroy the microphone.)
Interesting: When I switch off the microphone (shifting the left switch to the right), only the internal microphone is switched off, while the headset continues to work.
When I tested this some days ago, I thought, that the headset was switched off, too. Most likely, I did sth. stupid while testing. Now it just works as intended.
Problem solved 
That is what is supposed to happen. It’s a hardware switch for that particular microphone not a software mic mute button (think that’s the alternative function of one of the f-keys).