Repair/fix broken xbox controller?

 Hey guys, all of my original xbox controllers have decided to quit on me, there doesn't seem to be any damage on them on the outside, i think it mighgt have something to do with the cords. Does anyone know what's wrong and how i could fix it? Thanks.

I had a similar issue with a few of my old Gamecube controllers. There was one that the buttons didn't work, another that the joysticks didn't work, and another with both problems.

What I did was take out the good/working parts and combined them into one complete controller. It works pretty well, but the main joystick is missing the top peice, so it is a little awkward to use. Other than that, all works well.