What was found
APPROACHING DESTINATION, SHOWED RED X'S ON AIRSPEED, ALTITUDE, AND VSI. ALSO RED ATT FAIL AND RED HEADING FAIL. AFTER ARRIVAL, FOUND DISPLAY UNIT 4 BLANK. ACCESSED CMC DIAGNOSTICS & FOUND ALL MODULES TO BE REPORTING EXCEPT FOR DU 4, SHOWED NO COMMS, ATTEMPTED TO REWRITE SOFTWARE INTO DU 4, RECEIVED ERROR MESSAGES. SWAPPED DU 4 WITH DU 1. FOUND DISPLAYS TO BE WORKING NORMAL. REPOSITIONED DISPLAYS BACK TO ORIGINAL LOCATIONS. ALL DISPLAYS CONTINUED TO WORK NORMALLY. SWAPPED DU 3 & DU 4 FOR EVALUATION. CLEANED CONNECTORS ON RACKS & REINSTALLED DISPLAYS IN OPPOSITE POSITIONS. FOUND DISPLAY 3 INOPERATIVE. REPLACED DU 4 IAW MM 34-23-00. ACCESSED CMC & LOADED SOFTWARE. OPS CHECKED GOOD.