What was found
AT ROTATION, ESSENTIAL POWER FAIL LIGHT CAME ON MOMENTARILY THEN WENT OUT WITH NR 1 GENERATOR FAIL. UNABLE TO BRING NR 1 BUSSSM20ACD200A2 ON LINE. LOST THE FOLLOWING: CAPT'S INST LIGHTS, PITCH TRIM, ASYM FLAPS, NR 1 EPR WITH PACKS TRIPPED, NR 1 OIL TEMP WENT -40 DEGREES, SYS A-HYD WENT DOWN TO 2000 PSI, ENG FAIL LIGHTS CAME ON. CAME BACK AND LANDED UNEVENTFULLY. WATER INTRUSION FOUND ON E-1 ELECTRICAL SHELF FROM RAIN. AREA DRIED AND GCU CHANGED PRECAUTIONARY. REMOVED AND REPLACED NR 1 GCU AND VOLTAGE REGULATOR IAW B727-200MM 20-10-011. RAN ALL 3 ENGINES IAW 727 JRH CH5. ALL BUS TIES CLOSE.