What was found
EN ROUTE FROM PHX TO MCO, SMELLED A BURNING ELECTRICAL ODOR WITH VISIBLE SMOKE IN COCKPIT, WHILE DIVERTING TO DFW APPROXIMATELY 2 MILES LATER VENT EXTRACT FAULT LIGHT ILLUMINATED. MAINTENANCE PLACED SYSTEM ON MEL AND DEACTIVATED EXTRACT FAN. UPON ARRIVAL AT FIRST MAINTENANCE STATION, REPLACED AVIONICS COOLING (EXTRACT) FAN IAW AMM 21-26-51-04, OPERATIONAL CHECK WAS GOOD. SUPP - VENDOR CONFIRMED FAILURE OF AVIONICS COOLING FAN S/N 675, UNIT SEIZED, COULD NOT PERFORM INCOMING FUNCTIONAL CHECK. FOUND THE FRONT BEARING BROKEN, REAR BEARING LOOSE AND WORN, AND FRONT FLANGE CENTER HOLE WORN. REPLACED DEFECTIVE PARTS AND PERFORMED FUNCTIONAL TEST IAW CMM 21-26-42, REV 6.