What was found
INSPECTION TYPE: PS-10140Z, BLOCK TURN BACK TO AFTER COMPLETING THE LEFT ENGINE START THE LEFT A/S IN, ALTIMETER, VSI ALL WENT INOP, ALONG WITH LEFT TRASPONDER. SWITCHING TO ALT POS ON AIR DATA CORRECTED PROBLEM. AFTER BLOCKIN AND SWITCH TO APU ALL INSTUMENTS NORMOPERATIONAL CHECK OF LEFT ADC PER AMM 34-12-00-716 SHOWS NO FAULTS.