What was found
ON AUTO SLAT EXTENSION TEST SLATS FAIL TO EXTEND SMOOTHLY. CHANGED SOL VLV ASSY BORROWED FROM NWA, NOW FLAPS WILL NOT EXTEND HYD FOUND INPUT SHAFT SHEARED FROM THE FLAP DRIVE UNIT TO THE PDU. WHEN ACP AUTO SLAT EXTENSION TEST, SLATS START, STOP, THEN CONTINUE TO FULL DOWN, INSTEAD OF ONE MOVEMENT. BOTH LEFT AND RIGHT STALL SYS. REPLACED T/E FLAP POWER DRIVE VALVE ASSY.