What was found
NITROGEN GEN SYSTEM DEGRADED TO BLUE LIGHT. BLUE LIGHT ON. COMPLIED WITH MEL 4701. APPROVED PLACED ITEM ON MEL 4701B. DISCONNECTED OXY SENSOR INLET TUBE FROM SENSOR IAW 47-42-03-020. SMELLS OF FUEL. REPLACING SECONDARY BACKFLOW PREVENTION CHECK VALVE. REMOVED AND REPLACED SECONDARY BACKFLOW PREVENTION CHECK VALVE IAW 47-21-04-400-803. OPS CHECK GOOD IAW 47-00-00-790-802. BLUE DEGRADED LIGHT EXTINGUISHED GREEN LIGHT ILLUMINATED. READY TO CONTINUE.PARTS USED: 29-4721-9-0001, QTY :1 ROTABLE PARTS CHG:TT # 1358367 SN OFF 0831 PN OFF 29-4721-9-0001 IPC REFERENCE # NO COMPONENT FOUND.VALVE, CHECK, 0 OFF 29-4721-9-0001 3889 ON 29-4721-9-0001 9909 PERFORMED IDT INSP OF ALI ITEM OF NEADS LINE LEAK CHECK PER AMM 47-00-00-790-802. CHECK OK.