What was found
APPROX 5 MIN AFTER T/O, BOTH A-SYS LOW HYD PRESS LIGHTS ILLUMINATED AND THE A-SYS QTY DROPPED TO ZERO. A-SYS PRESS REMAINED AT APPROX 2000 PSI, BUT OSCILATED FROM 1500-2400 PSI AFTER CK LIST COMPLETE A-SYS QTY ROSE TO 1.7. ALL CK LIST COMPLIED WITH AND AIRCRAFT RETURNED TO MEM. FOUND O/B FLAP CONTROL VALVE LEAKING OUT OF CONTROL SLIDE. REMOVED AND REPLACED SAME IAW MM 27-51-51. CYCLED FLAPS SEVERAL TIMES, FLAPS AT ALL TIMES WITHIN LIMITS. SERVICED ALL HYD RESERVOIRS TO FULL P/N ON 65-40449-4 OFF 65-40449-3 S/N ON UP14335 OFF DBP371/79.