What was found
ON INITIAL DECENT, LEFT BLEED TRIP OFF LIGHT ILLUMINATED. RESET TRIP IAW QRH, LIGHT STAYED OUT, EXTINGUISHES. ACFT GROUNDED. PERFORMED FIM TASK 36-10-809, WRENCH CHECKED ALL VALVES. VALVES CHECK OK. AS PRECAUTIONARY MEASURE, REPLACED HIGH STAGE REGULATOR REF AMM 36-11-07. GROUND VERIFICATION CHECK SUCCESSFUL. PERFORMED HEALTH CHECK IAW TASK CARD NG-36WC-00001 FAILED STEP 4J. HIGH STAGE CONTROL PRESSURE CHECK, R & R HIGH STAGE VALVE IAW AMM 36-11-06. COMPLETED HEALTH CHECK TASK CARD FROM STEP 4J. ALL TESTS PASSED.