What was found
(CAN) FOLLOWING TAKE OFF, CONTINUOUS LOUD DINGING ALARM, #4 MFD BLANKED, LOST ALL CAS MESSAGES. FLAP INDICATION CYCLING BETWEEN AMBER AND GREEN. LOST ABILITY TO USE HEADING, VERTICAL OR F/D MODES. DECLARED EMERGENCY, RETURNED TO AIRPORT WITH TOWER VECTORS, VISUAL APPROACH. LANDED UNEVENTFUL. APPROX. 45 SECONDS AFTER LANDING ALL SYSTEMS RETURNED TO NORMAL (TC# 20190410020)