Letter Buttons (X,Y,A,B) Do not work

One of my buddies brought me a controller without working letter buttons. I wanted to ask before opening it, what should I be looking for or expect inside of this controller?

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 1
crwdns2934285:0crwdne2934285:0