What was found
ELECTRICAL SHORT CIRCUIT SMELL WAS FELT BEFORE TAKEOFF AT GND, RETURN WAS DONE. IAW AMM 21-26-51 PB 401 THE BLOWER FAN WAS REPLACED IAW ESPM 20-46-10 THE CB 1HQ AVNCS VENT BLOWER FAN WAS REPLACED & IAW ESPM 20-44-11 THE CONNECTOR 20 HQA WAS REPLACED. IAW AMM 24-51-55 P 401 THE CONTACTOR 8HQ BLOWER FAN CTL AVCNS VENT WAS R & R IAW AMM 21-26-00-710-001-A. OPERATIONAL CHECK OF THE AVIONICS EQUIP VENTILATION SYS VIA MCDU WAS PERFORMED WITH SATISFACTORY RESULTS. PN EVT3454HC SN OFF 164900864 SN ON 164903466.