What was found
AT 3500 FEET WE HAD SMOKE IN THE COCKPIT FROM THE DU4. WE SMELLED ELECTRICAL FIRE THE MFD 2 CIRCUIT BREAKER TRIPPED. UPON ARRIVAL THE MFD 2 CIRCUIT BREAKER WAS DISENGAGED. APPLIED POWER AND AVIONICS TO AIRCRAFT WITH NO DEFECTS NOTED. ENGAGED MFD 2 BREAKER AND IMMEDIATELY THE MFD 2 BREAKER DISENGAGED AND A STRONG SMOKE ODOR WAS VENTED THROUGH THE RT GLARE SHIELD AVIONICS FAN. REMOVED THE NR 4 DISPLAY (MFD 2) AND VISUALLY INSPECTED WIRING WITH NO DEFECTS NOTED. ENGAGED THE MFD 2 BREAKER AND APPLIED POWER AND AVIONICS TO AIRCRAFT. BREAKER REMAINED ENGAGED EVEN WHILE MANIPULATING ASSOCIATED WIRING. STRONG SMOKE SCENT WAS PRESENT FROM THE REMOVED FAILED PART NO: 7014300-901 SERIAL NO: 0302C466 NR 4 DISPLAY (MFD 2) COOLING FAN AREA. R&R DU4 (MFD2). APPLIED POWER TO AIRCRAFT FOR 2.0 HOURS WITH NO DEFECTS NOTED. GROUND OPERATIONAL CHECKS SATISFACTORY. ALL WORK ACCOMPLISHED IN ACCORDANCE WITH MM CHAPTER 34-25-01 (REV 44).