Remove the earpad by twisting counterclockwise and firmly holding the earcan with the other hand. Once you have removed the earpad, you can unscrew the 4 small screws. Then you must unscrew the central screw that locks the headphone to the micro. After that, you have to carefully but strongly pull the inner plastic part. There, 4 more screws are revealed which can be unscrewed to access the mic part. In my case the faulty cable was the one going from the mic part to the headphone (presumably due to a bad design). I used a multimeter to test which one of the four (+/- left and right) was failing, and soldered a new cable. Now is working but I don't think it will last too long.