What was found
FUEL IMBALANCE BEGAN AT FL 380 ABEAM SPOKANE, WA. NO INDICATION OF TOTAL LOSS OF FUEL, ONLY 2,600 # IMBALANCE BETWEEN MAIN TANKS. COMPLETED "FUEL LEAK-ENGINE" QRH CHECKLIST AND SHUTDOWN #2 ENGINE. NORMAL LANDING AT PDX. NO UNUSUAL FLIGHT CHARACTERISTIC OR ROLLING TENDENCIES. GROUNDED - YES. INITIAL EVALUATION, NO CROSSFEED VALVE LIGHT ON FUEL PANEL AT OVERHEAD. RELAMPED PUSH BUTTON LIGHT, NO HELP. DISCOVERED CB FOR CROSS FEED VALVE, PG-3 B7, POPPED/FOUND OPEN. PERFORMED BC RESET PROCEDURE AND INSPECTION IAW B737-800 AMM 20-60-01, NO DEFECTS NOTED. CB RESET, POPS OPEN WITHIN 5 SECONDS. DISCONNECTED CONNECTOR AT CROSSFEED VALVE, D792 AT V39. RESET CB, STAYS RESET/IN. PULLED AND COLLARD CB AGAIN. SUSPECT BAD CROSSFEED VALVE ACTUATOR MOTOR. RECONNECTED D792. WHILE PERFORMING T/C, FOUND FQIS DEFECT. REF LP 60239088. REMOVED AND REPLACED FUEL CROSSFEED ACTUATOR REF AMM 28-22-21 OPS CHECK GOOD. INDICATIONS IN FLIGHT DECK NORMAL.