As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER DEICE BOOTS WERE CYCLED AND AN I.F.R. LANDING APPROACH WAS ENTERED, ALL PRESSURE GYRO INSTRUMENTS FAILED AND SYSTEM PRESSURE WENT TO ZERO. BOTH RED INDICATOR BALLS REMAINED IN. FOUND LT CHECK VALVE IN MANIFOLD DEFECTIVE AND LT PUMP OUTPUT LOW. CHANGED BOTH ITEMS, BUT SUSPECT DEICE VALVE STAYED OPEN TOO LONG.