What was found
COCKPIT SMOKE: ON THE GROUND WITH MAIN CABIN DOOR OPEN, SHUT DOWN APU MOMENTARILY. ON RE-START, SMOKE CAME FROM COCKPIT AREA AND QUICKLY FILLED CABIN. NO DISCERNABLE, OIL, ELECTRICAL OR OTHER NORMAL SMELL. SHUT DOWN APU AND ALL ELECTRICS AND LEFT AIRPLANE FOR SMOKE TO CLEAR. PERFORMED OPS CHECK OF APU WITH NO DEFECTS NOTED. RAN APU FOR APPROX 45 MINUTES, NO SMOKE OR FUMES NOTED INSIDE OR OUTSIDE AIRCRAFT. BORESCOPED APU INLET AND EXHAUST FOR OIL OR DEBRIES, NO DEFECTS OR LEAKS FOUND. OPS CHECK GOOD AT THIS TIME