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747-400
MAINTENANCE MANUAL

The MP module in the R/T performs the system monitoring functions. The module has a timing and control (T&C) microprocessor, power supply monitor, discrete monitor, antenna stabilization, fault memory, data bus, receivers and decoders and various other circuits.Initially after power turn on the power supply monitor checks various dc voltage levels. The monitor also receives a temperature sensor input to detect an overheat condition in the mount cooling system. The MP codes the fault condition and stores it in the fault memory.During each R/T transmit/receive period of operation, the MP module checks the operation of the receiver/transmitter and antenna. The antenna stabilization and drive circuits stabilization processor performs software tests on its own circuits, antenna drive circuits, the antenna unit and inertial reference unit (IRU) inputs. Any fault conditions are sent from the antenna stabilization processor to the MP. The MP codes the fault condition and stores it in the fault memory.Normal power supply voltages and temperature causes the MP to enable the BITE circuit antenna stabilization microprossor. When a fault is detected the microprocessor goes through a fault routine to locate the fault condition. Faults are sent by a data bus to the MP which codes the fault condition and stores it in the fault memory.The BITE monitoring circuits in the timing control checks each of the weather radar unit functions to determine which replaceable unit or units are faulty. The BITE circuits generate fault messages which are sent through the ARINC 453 left and right bus No. 2 to the NDs.When a fault is detected the receiver/transmitter master processor also stores the fault in the fault memory for display on the liquid crystal display (LCD) on the R/T front panel. The TEST pushbutton on the R/T front panel must be pushed to display the fault(s) on the LCD. For additional information on the operation of the LCD and pushbuttons refer to the Self Test and Isolation paragraph below.
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 34-43-00
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A
747-400
MAINTENANCE MANUAL

 (8)  
Central Maintenance Computer (CMC) Functions

 (a)  
An ARINC 429 transmitter sends continuous maintenance status data to the CMC which is displayed on the CDUs. The CDU's can also request past weather radar maintenance flight data from the CMC memory.

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The left and right CMC sends flight beginning and end commands to the respective left and right weather radar R/Ts on the connecting data busses. If both CMCs fial, an air/ground relay defines the flight legs.

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ND Weather Radar Display Functions

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For normal weather radar operation, the ND's provide the weather displays during the EFIS operating modes of APP, VOR, MAP and CTR MAP.

 (b)  
The ND's are microprocessor-controlled. The captain's ND receives video on the left and right data bus 1. The first officer's ND receive video on the left and right data bus 2. Weather radar data is displayed on the ND's when the captain's or first officer's EFIS control panel WXR switch/indicator is on. A summary of the input data to the ND's is as follows:

 ~......................................................... | Captain's ND Signals | From | ........................................................... | Video on Left Data Bus 1 | R/T 1 | ........................................................... | Video on Right Data Bus 1 | R/T 2 | ........................................................... | On/Off Enable | Left CDU | ........................................................... | Range | Left CDU | 2..................................…......................1 ~......................................................... | First Officer's ND Signals | From | ........................................................... | Video on Left Data Bus 2 | R/T 1 | ........................................................... | Video on Right Data Bus 2 | R/T 2 | ........................................................... | On/Off Enable | Right CDU | 2..................................…......................1
　
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