A320 FLC WITH ELECTRICAL ODOR IN THE COCKPIT DECLARED EMER AND RETURNS TO DEP ARPT.

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RETURN TO FIELD DUE TO BURNT ELECTRICAL ODOR IN COCKPIT. ON TKOF; AFTER INITIAL PWR REDUCTION; HEARD A LOUD CLUNK LIKE A RELAY OPENING FROM COPLT'S SIDE PANEL. #2 MCDU WENT BLANK AND STRONG BURNT ELECTRICAL ODOR FOLLOWED. CONTINUED TKOF PROFILE AND AFTER CLEAN-UP AND TKOF CHKLIST; ECAM DISPLAYED 'HOT AIR TRIM FAULT.' #2 MCDU CAME BACK ON; ELECTRICAL ODOR SOMEWHAT DISSIPATED; BUT STILL STRONG ENOUGH FOR US TO CONSIDER USING OXYGEN MASKS. #2 MCDU INTERMITTENTLY WENT BLANK WHILE ECAM HOT AIR TRIM DISAPPEARED THEN REAPPEARED. DID NOT THINK IT WAS PRUDENT TO CONTINUE TO LAX SO I REQUESTED A RETURN TO THE FIELD. ALSO I WAS CONCERNED THAT WE STILL HAD NOT DETERMINED THE SOURCE OF THE BURNT ELECTRICAL ODOR AND THE POSSIBILITY THAT AN ELECTRICAL SHORT/FIRE IN THE AVIONICS MAY BE CAUSING THE ANOMALIES. SO I DECLARED AN EMER AND DID AN OVERWT LNDG. WE DID CONTACT DISPATCH DURING THE FLT AND THEY WERE ABLE TO PROVIDE SUPPORT. DID A CABIN ADVISORY WITH THE FLT ATTENDANTS. ONCE ON THE GND AND SIT STABLE; WE DID A NORMAL TAXI TO GATE. PRELIMINARY MAINT FINDING WAS THE '#2 MCDU INOP AND HAS BURNT SMELL FROM BACK OF UNIT.' ALL OUR ACTIONS WERE BASED ON THE FACT THAT WE COULD NOT DETERMINE THE SOURCE OF THE BURNT ELECTRICAL ODOR IN THE COCKPIT NOR WHETHER THE PROB WAS CONTAINED OR NOT.