What was found
RNO - BURNT SMELL NOTICED BY FLIGHT ATTENDANT, RAMP AGENT IN FRONT OF CABIN. WHEN COCKPIT DOOR OPENED PILOT SMELLED THE ODOR ALSO. CHECKED FOR POPPED C/B'S, NONE NOTED. RAN UP BOTH ENGINES AND APU, OPERATED BOTH PACKS, OPERATED TEMP SWITCHES FOR ABOUT 5 MINUTES, UNABLE TO DUPLICATE SMELL. RETURNED TO SERVICE. NO PARTS REPLACED.