What was found
TRANSPONDER FAIL LIGHT ILLUMINATED AFTER TAKEOFF, ATC WAS NOT RECEIVING TRANSPONDER SIGNAL. AIRCRAFT IS CONFIGURED WITH ONLY ONE TRANSPONDER AND RETURN FROM ARRIVAL DESTINATION WOULD NOT BE PERMISSIBLE. AIRCRAFT ADVISED TO RETURN TO DEPARTURE STATION. AIRCRAFT SWAPPED WITH 266US AND FERRY FLIGHT CONTINUED MBJ. ATC TRANSPONDER TROUBLESHOT TO INOPERATIVE TRANSMITTER, FAIL LIGHT ILLUMINATED ON RT, REMOVED AND REPLACED TRANSMITTER, P/N 4061400-905 FROM STOCK ROOM. AIRCRAFT RETURNED TO SERVICE. (M)