What was found
DURING CRUISE FLIGHT, CREW NOTED THAT ISO VALVE CAUTION LIGHT ILLUMINATED. HYDRAULIC QUANTITY OF NR 1 SYSTEM HAD DROPPED TO 1 QUART. CREW ADVISED MAINTENANCE CONTROL AND DECISION WAS MADE TO DIVERT TO MDT. AIRCRAFT LANDED WITH 0 DEGREE FLAP SETTING, TAXIED TO RAMP AREA AND WAS THEN TOWED TO GATE. MAINTENANCE DISCOVERED PROBLEM WITH NR 1 ENGINE DRIVEN HYDRAULIC PUMP AND REPLACED THAT UNIT. OPS AND LEAK CHECKED PUMP IAW MM PROCEDURES. ALL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.