What was found
AC RETURNED, DUE TO TRANSPONDERS FAILED AND NO RADAR CONTACT WAS REPORTED BY CONTROL TOWER. MAINT PERFORMED AUTO TEST IN THE TRANSPONDER 1 AND 2 IAW MM 34-54-00, ALL CORRECT. AC WAS SENT TO THE HANGAR AND SYSTEMS WERE TESTED WITH TESTER MODEL TR-220 AND (C) AND (S) MODE WERE DETECTED OUT OF SERVICE. THE TRANSPONDER/TCAS CONTROL PANEL WAS REPLACED FOR THE (S) MODE IAW MM 34-54-03, TESTED CORRECT. IN THE (C) MODE THE WIRING WAS DETECTED DAMAGED, THEREFORE WIRING WAS REPAIRED IAW EO983490, TESTED CORRECT.