What was found
THE PASSENGER OXYGEN SYS IN THE CABIN FAILED TO DEPLOY, IN MANUAL OR IN AUTOMATIC MODE, WHEN TESTED. ONLY THE LT ROW, FROM SEAT 1 TO THE OVER-WING EXITS, FUNCTIONED. MX FOUND A WIRE (W636E220) HAD SHORTED TO GROUND AT TERMINAL NR 8 ON STRIP 53-154. THE CORRECTIVE ACTION WAS TO RE-SEAT THE PSU CONNECTOR AT ROW 2. OPS CHECK OF THE PASSENGER OXYGEN SYS WAS SATISFACTORY PERFORMED IN BOTH MANUAL AND AUTOMATIC DEPLOY MODES. THE ACFT HAS RETURNED TO SERVICE.