F.
Brake control system fault messages on the CDU.

 (1)  
Fault messages describe malfunctions and identify the affected LRU. These messages come into view on the CDU when a test fails or existing faults recall is done. These are the fault messages applicable to the brake control system:

 (a)  
ANTISKID TRANSDUCER -(number 1 thru 16 specified) FAIL A bias current is transmitted through the transducer coil and back to the control unit. The voltage across the transducer is monitored by the main wheel card and compared to voltage limits programmed into the data aquisition BITE card. Any voltage on a transducer circuit that is outside these limits is registered as a fault. The bias current is approximately 10 mA. Greater than 9.5 vdc is computed as an open circuit. Less than 2.5 vdc is computed as a short circuit.

 (b)  
NORMAL ANTISKID VALVE -(number 1 thru 16 specified) FAIL A bias current is transmitted through the servo coil in the antiskid valve and back to the control unit. The voltage across the valve is monitored by the control unit and compared to voltage limits programmed into the data aquisition BITE card. Any voltage on a valve circuit that is outside these limits is registered as a fault. The bias current is approximately 5 ma. Less than 0.23 Vdc is computed as a short. Higher than 18 Vdc is computed as an open circuit.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 (c)

(d)

(e)

(f)

(g)

(h)

(i)

A
747-400
MAINTENANCE MANUAL

ALTERNATE ANTISKID VALVE (number 1 thru 16 specified) FAIL Fault isolation functions the same as for the normal antiskid valve described above.IRU-L>BSCU INPUT FAIL (Captain's Select) Circuits in each main wheel card and the autobrake card receive IRS signals. Each card has a receiver and a circuit that monitors and compares the data. The message occurs when:
 -No IRS message is received
 -IRS digital message is formatted incorrectly
 A data disagreement is computed as a BSCU FAIL.
IRU-R>BSCU>INPUT FAIL (First Officer's Select)
 Circuits in each main wheel card and the autobrake card receive
 IRS signals. Each card has a receiver and a circuit that
 monitors and compares the data. The message occurs when:

 -No IRS message is received
 -IRS digital message is formatted incorrectly
 A data disagreement is computed as a BSCU FAIL.
BRAKE TORQUE SENSOR -(number 1 thru 16 specified) FAIL
 Circuits in the brake torque limiter cards monitor excitation
 voltages in the brake torque sensor circuits and sensor output.
 This fault message occurs when any of these conditions are
 detected in the sensor circuit:

 -Open circuit in the sensor or line
 -Short circuit in the sensor or line
 -Brake torque sensor cannot be zeroed because offset
 signal is too large (More than 5000 lb ft)BRAKE TORQUE CONTROL (left front, right front, right rear or left rear specified) CHANNEL FAIL The data aquisition BITE card monitors the power supply output of the specified card and compares it to values programmed into the data aquisition software. If the voltage on the circuit is outside the programmed range, the brake torque control channel is registered as failed. The data aquisition BITE card also monitors the brake torque control channel for microprocessor and other hardware failures.ANTISKID CONTROL CHANNEL (number 1 thru 16 specified) FAIL The data aquisition BITE card monitors the power supply output of the specified card and compares it to values programmed into the data aquisition software. If the voltage on the circuit is outside the programmed range, the Antiskid control channel is registered as failed. The data aquisition BITE card also monitors the antiskid channel for microprocessor and other hardware failures.AUTOBRAKE AIR/GND INPUTS DISAGREE The discrete air/ground signals from the PSEU are monitored to make sure they agree (both open circuit or both ground). If the signals do not agree for more than 1.6 seconds, this error signal is stored as a fault.
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