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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
D. The shutoff valve pressure switch is located at the shutoff valve output and monitors the shutoff valve operation. The switch opens above 1000 psi to provide a logic "high" with autobrake selected. The switch goes to the relaxed position to provide a logic "ground" signal when the autobrake selector switch is in any of the four autobrake selected positions and pressure falls below 1000 psi. Any incorrect logic will disarm the autobrake and illuminate the disarm light. The control servo valve pressure switch monitors the servo valve output pressure to detect control system faults. The switch is connected to the fault monitor logic to indicate high pressure (above 1000 psi) with an open circuit and indicates low pressure (below 1000 psi) with a closed (logic ground) circuit.
Autobrake Shuttle Valves (Fig. 1)
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A. Two shuttle valves, located on the left aft bulkhead of the left gear wheel well, are installed in the autobrake system, one in each of the two brake pressure lines upstream of the left and right normal antiskid valves. The valves sense hydraulic pressure from the autobrake pressure control module and from the brake metering valves. The shuttle valve will port pressure to the antiskid valve from the source (autobrake pressure control module or brake metering valve) of highest pressure.
Hydraulic Pressure Switches (Fig. 1 and 3)
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A. Pressure switches (S762 LH, S763 RH), identified as brake pedal pressure switches, sense the B system brake pressure downstream from the brake metering valves. The switches are attached to respective autobrake shuttle valves and actuate when manually metered hydraulic BRAKE pressure is greater than 750 psi. They provide a ground signal to the autobrake circuit to deactivate autobraking.
Autobrake Digital Circuits and Test Switch (Fig. 3)
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A. The autobrake digital circuits are located in the antiskid control unit (located on the E3-2 electrical shelf). The microprocessor system consists of a central processing unit and counter-timer circuit driven by a crystal controlled clock, a non-volatile memory (EPROM), a random access memory (RAM), and input/output circuitry. Supporting components include a transducer input multiplexer, valve driver, disarm control circuit, and a 5 VDC power supply. Signals from the autobrake circuit operate the autobrake pressure control module which initiates and controls brake pressure as required to meet the selected airplane deceleration rate. The autobrake system performs a self-check each time the system is turned on.
B. To test the autobrake system, the antiskid control unit has incorporated an amber autobrake test light and an autobrake test switch, located on the front face of module (Fig. 1). The switch functionally tests the autobrake system. The test is done with the AUTO BRAKE selector switch in any decel position other than OFF.
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32-43-01
ALL ú ú 01 Page 7 ú Mar 15/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
FROM A/B ON RELAY
TO SYS B RETURN
TO SOLENOID SW INPUT
TO A/B DISARM LIGHT
TO SERVO SW INPUT
HYD SYS B PRESSURE
FILTER
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