What was found
APPROXIMATELY 30 MINUTES AFTER LEVEL OFF, AT FL400 EICAS LT BLEED OFF. COMPLIED WITH QRH, CABIN ALTITUDE MAINTAINED APPROX 30 MINUTES LATER RT BLEED OFF. RAN QRH AFTER COMMENCED DESCENT FROM FL400 TO 10,000, GOT CABIN ALT EICAS, RAN QRH, O2 MASK ON. RESET RT ENG & LT ENG. BLEED VALVES, ESTABLISH PRESSURIZATION & CABIN ALTITUDE & LEVELED AT 15,000 FT & STATUS MSSY, CAB ALT AUTO 1. RAN ENGINES AS PER JRH AND ENGINE RUN FORM AND OPS CHECKED AND LEAKED CHECKED REVERSE FLOW CONTROLLER VALVE , OPS CHECKED NORMAL. OPS CHECKED THE COMPLETE PNUE . SYSTEM AS IAW AMM-36-11-00-5-0, EVERYTHING OPS CHECKDED NORMAL AS IAW AMM. ACFT OK TO CONTINUE.