What was found
(CAN) ON JULY 25, 2000 CREW REPORTED UPON SELECTION OF APU BLEED AIR ASSOCIATED INDICATOR. OF LOAD CONTROL VALVE OPENING HAD FAILED. A/C MAINT ENGINEER OPENED EXTERNAL AIR SOURCE PANEL ONLY TO FIND APU FAULT INDICATOR PANEL HAD MELTED. FURTHER INVEST. FOUND THAT APUS LOAD CONTROL VALVE FILTER HAD DEPARTED FROM VALVE ASSY & TRAVELLED THROUGH PNEUMATIC PLUMBING EVENTUALLY JAMMING CHECK VALVE LOCATED AT EXTERNAL AIR SOURCE COUPLING. RESULTANT 10TH STAGE AIR LEAKED INTO ACCESS PANEL AREA & HEATED APU FAULT PANEL TO POINT OF MELTING IT. THE FAULT PANEL WAS ISOLATED, PNEUMATIC SYS INSP & A NEW LOAD CONTROL VALVE INSTALLED, DISCREPANCY RECTIFIED.