TC reported that the cab door opened byitself as the train was departing and EB was applied. Closedcab door and reset EB - ok. Train proceeded to next station in AM. TC reported that the cab door opened by itself as th  ~~~~~ Check and found #3541 A/S cab door top cable snap causing cab door tounge to be stuck. Replaced top cable and function check cab door tounge - smooth opeation. Security check-ok. Done by: Sateesh and Asruddin