TM 1–1520–238–T–3
18–2
MULTIPLEX READ CODE INTERPRETATIONS
18–1 SIGNAL NAME:
APU START SW
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
16
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors auxiliary power unit (APU) START/RUN/OFF switch.
REMARKS: From APU/Fire test panel through digital automatic stabilization computer (DASEC)
multiplex remote terminal unit (MRTU) to fire control computer (FCC).
PASS:
If second digit on heads out display (HOD) is 1, 3, 5, or 7, go to paragraph 18–2.
FAIL: Location of fault: APU/Fire test panel, wiring from APU/Fire test panel 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).
18–2 SIGNAL NAME:
APU OIL PRESSURE LOW
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
15
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU oil pressure.
REMARKS: From low oil pressure sensor through APU speed electronic control unit and DASEC to
FCC.
PASS:
If second digit on the HOD is 2, 3, 6, or 7, go to paragraph 18–3.
FAIL: Location of fault: low oil pressure sensor, wiring from low oil pressure 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).
18–3 SIGNAL NAME:
APU OVERSPEED IND
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
14
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU speed sensor.
REMARKS: From APU speed sensor through APU speed electronic control unit and DASEC to FCC.
PASS:
If second digit on the HOD is 4, 5, 6, or 7, go to paragraph 18–4.
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).
18–4 SIGNAL NAME:
APU IGNITION
MEMORY LOCATION: 002131
MEMORY DATA BIT(S):
13
(BINARY)
CONDITION:
(None)
SIGNAL FUNCTION:
Monitors APU ignition unit.
REMARKS: From APU ignition unit through APU speed electronic control unit and DASEC to FCC.
PASS:
If third digit on the HOD is 1, 3, 5, or 7, go to paragraph 18–5.
FAIL: Location of fault: APU ignition unit, wiring from APU ignition unit 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).
