What was found
(CAN) DURING THE ACFT RUNUP, THE PILOT SELECTED FLAPS DOWN. AT 30 DEGREE OF FLAP DOWN POSITION, A NOISE WAS HEARD AND THE FLAPS STOPPED. THE ACFT TAXIED BACK TO THE RAMP. AFTER INSPECTION, THE RT CONTROL SPROCKET, PN 0861500-71 ON THE FLAP ACTUATOR WAS FOUND BROKEN. THE BREAK WAS WHERE THE ATTACHING PIN, PN 0861500-70 GOES THROUGH THE SPROCKET AND ACTUATOR DRIVE SHAFT ASSY.