(5)
If the APU is stopped for an APU usual shutdown and the OVER SPEED light comes on, there is a possible malfunction in the automatic protection system. You should do a check of the electronic speed switch as a possible cause of this malfunction.
(6)
If there is an automatic shutdown during the APU operation and the OVER SPEED light comes on, specified maintenance must be done to prevent damage to the APU.
(a)
APU CONTROL UNIT WITHOUT THE TEST FAIL AND TEST PASS LIGHTS; To make the OVER SPEED light go off, you must push the OVERSPEED RESET switch on the APU control unit.
(b)
APU CONTROL UNIT WITH THE TEST FAIL AND TEST PASS LIGHTS; To make the OVER SPEED light go off, you must push the OVERSPEED RESET/TEST switch on the APU control unit.
O. Many problems have symptoms that you can see or hear in the area of the APU.
(1) You can use an observer to identify symptoms such as these:
(a)
Smoke in the air conditioning system
(b)
Unusual noise from the APU
(c)
Fire or smoke in the APU exhaust duct
(d)
Fluid that flows from the APU drains.
3. Troubleshooting Tips
____________________
A. Standard Tools and Equipment
(1) Multimeter - Simpson 260
B. References
(1)
AMM 20-10-07/201, E/E Rack Mounted Components
(2)
AMM 20-40-12/201, Electrostatic Discharge Sensitive Devices
(3)
AMM 49-11-00/201, APU Power Plant
C. Access
(1)
Location Zones
703 APU Compartment
(2)
Access Panels
3804 APU Cowl Door
D. Prepare for Troubleshooting
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49-00-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
WARNING:_______ DO NOT TOUCH THE IGNITION COMPONENTS UNTIL YOU DO THESE STEPS.
THESE STEPS WILL RELEASE THE HIGH VOLTAGE FROM THE IGNITION
UNIT. IF YOU DO NOT OBEY THIS PROCEDURE, INJURY TO PERSONS CAN
OCCUR.
CAUTION: TO PREVENT DAMAGE TO THE APU, MONITOR THE APU OPERATION LIMITS
_______ DURING THE APU OPERATION (AMM 49-11-00/201).
FOLLOW THE STARTER DUTY CYCLE WHILE YOU INVESTIGATE THE APU PROBLEMS. HIGH ENERGY STARTERS ARE EASILY OVERHEATED AND DAMAGED.
MAKE SURE THERE IS FUEL AT THE FUEL CONTROL UNIT WHEN YOU OPERATE THE APU. DAMAGE TO THE FUEL CONTROL UNIT CAN OCCUR IF THERE IS NO FUEL LUBRICATION.
MAKE SURE THE APU OIL LEVEL IS SATISFACTORY. DAMAGE TO THE APU ENGINE CAN OCCUR IF THERE IS NOT SUFFICIENT OIL FOR LUBRICATION.
(1) If you will touch the ignition components, do these steps to release the high voltage from the ignition unit:
(a)
Make sure 5 minutes have gone by since the last APU start.
(b)
Disconnect the igniter cable from the igniter plug.
(c)
Ground the igniter cable to the APU.
CAUTION: YOU MUST CAREFULLY DO THE STEPS IN THE TASKS BELOW TO REMOVE
_______ AND TO INSTALL THE APU CONTROL UNIT. A FAILURE TO DO THE STEPS CORRECTLY CAN CAUSE DAMAGE TO THE EQUIPMENT.
(2)
Do these tasks to remove the APU control unit:
(a)
"Rack Mounted E/E Box Removal" (AMM 20-10-07/201).
(b)
"ESDS Metal Encased Units Removal" (AMM 20-40-12/201).
(3)
Do these tasks to install the APU control unit:
(a)
"Rack Mounted E/E Box Installation" (AMM 20-10-07/201).
(b)
"ESDS Metal Encased Units Installation" (AMM 20-40-12/201).
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