What was found
AT FL 330, ATS LEVER DROPPED OFF, NR 1 A/P DROPPED OFF ALONG WITH A PUFF OF SMOKE VISIBLE BE GLARESHIELD FLOOD LIGHTS. ATS RE-ENGAGED AS DID THE NR 1 A/P. NO FURTHER "PUFFS" OF SMOKE. NO FURTHER PROBLEMS. PERFORMED MTP AFS BITE AND FMC BITE, BOTH FAULTED FCU LAST FLIGHT. REMOVED FCU AND NOTED BURNT SMELL FROM AFT VENT HOLE OF FCU. INSPECTED FCU CONNECTOR AND C/P PINS. NO FAULTS NOTED. INSTALLED NEW FCU PER AMM 22-15-12-4. PERFORMED AFS/LAND TEST PER AMM 22-40-00-5. ALL OPS CK OK. ACFT OK TO CONTINUE. DOWNGRADED A/P NR 1 TO CK II PRECAUTIONARY AND A/P NR 2 REMAINS CAT II.