Persisting I/O issue

I bought this laptop few months back. Still in warranty. 

A month back speaker and mic stopped working completely. Updated all drivers, but to no avail.

Raised service ticket. Engineer came home, replaced the motherboard. It was a badly repaired one. Immediately started giving massive screen flicker. Engineer replaced original board back and went back.

Today, he came with another board. Seems it is another bad repair job. 

While speaker is now working, mic is still not working. Engineer is still working for over 3 hours, opened up everything, reset everything, updated everything but still the mic doesn't work. He's still trying but about to give up.

I am fed up. Will Dell be gracious enough and replace this faulty laptop with a new one?