TM 1–1520–238–T–3
18–4
Change 4
18–9 SIGNAL NAME:
APU OVERTEMP IND
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
8
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU engine gas turbine (EGT) temperature.
REMARKS: From APU thermocouple through APU speed electronic control unit and DASEC TO
FCC.
PASS:
If fourth digit on the HOD is 4, 5, 6, or 7, go to failure symptom index and next failure symptom
paragraph.
FAIL: Location of fault: APU thermocouple, wiring from APU thermocouple to APU speed electronic
control unit, wiring from APU speed electronic control unit to DASEC. Troubleshoot wiring to
isolate fault (TM 1–1520–238–T–8).
18–10 SIGNAL NAME:
APU RPM
MEMORY LOCATION: 002134
MEMORY DATA BIT(S):
4–19 (ACY) 4–15 (ACZ)
(SCALAR)
CONDITION:
Monitor HOD while APU is spooling up; memory location response digits should
increase as APU revolutions per minute (RPM) increase.
SIGNAL FUNCTION:
Monitors APU RPM.
REMARKS: From APU speed sensor through APU speed electronic control unit and DASEC to FCC.
PASS:
Location of fault if CONDITION has been met: replace FCC (TM 9–1230–476–20–1).
FAIL: Location of fault: APU speed sensor, wiring from APU speed sensor to APU speed electronic
control unit, wiring from APU speed electronic control unit to DASEC. Troubleshoot wiring to
isolate fault (TM 1–1520–238–T–8).
18–11 SIGNAL NAME:
APU EXHAUST TEMP
MEMORY LOCATION: 002133
MEMORY DATA BIT(S):
4–19 (ACY) 4–15 (ACZ)
(SCALAR)
CONDITION:
Monitor HOD with APU running; memory location response digits should increase as
temperature increases.
SIGNAL FUNCTION:
Monitors APU EGT temperature.
REMARKS: From APU thermocouple through APU speed electronic control unit and DASEC to FCC.
PASS:
Location of fault if CONDITION has been met: replace FCC (TM 9–1230–476–20–1).
FAIL: Location of fault: APU thermocouple, wiring from APU thermocouple to APU speed electronic
control unit, wiring from APU speed electronic control unit to DASEC. Troubleshoot wiring to
isolate fault (TM 1–1520–238–T–8).
18–12 SIGNAL NAME:
APU IGNITION
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
13
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU ignition unit.
REMARKS: From APU speed electronic control unit to DASEC.
PASS:
Location of fault if third digit on the HOD is 0, 2, 4, or 6: replace APU speed electronic control
unit (TM 1–1520–238–T–8).
FAIL: Location of fault: APU speed electronic control unit, wiring from APU speed electronic control
unit to DASEC, DASEC. Troubleshoot wiring to isolate fault (TM 1–1520–238–T–8).
