747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航1(61)

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 (c)  The self-test mode does not check: 1) Operation or accuracy of either temperature probe. 2) Operation or accuracy of either pressure transducer. 3) Operation of SSEC circuitry. 4) Output functions of altitude, airspeed and mach hold or
 altitude rate-of-change. 5) Operation of digitizer encoder ground line "automatic
 disconnect."
 6)  Failure annunciators (they are suppressed during this mode)
 7)  Those output functions and warning flags connected to
 systems without direct air data readouts.
 B.  Controls
 (1)  During the normal operating mode, the only controls that govern the central air data system operation are circuit breakers on the electronic circuit breaker panel (P7). On this panel there are two circuit breakers for each central air data computer, one to control the 115 volt, single phase 400 Hz power input and the other to control the 26 volt, single phase, 400 Hz synchro excitation. All controls and indicators on the front panel of each central air data computer (Fig. 1) come into use only with functional tests and/or failure indications and play no part in normal operation.
 EFFECTIVITY

 
 ALL  03 Page 21  Aug 25/8734-12-00
 CENTRAL AIR DATA COMPUTER SYSTEM - TROUBLE SHOOTING
___________________________________________________
 1.  General
_______
 A.  The following trouble shooting procedures are based on performance of the system operational test and are presented in tree-type format. The test steps (heavy-line box) are connected by shaded arrows to show the OK condition path. When all steps in the OK condition path check out, the system is operable.
 B.  When a test step does not check out, follow the NOT OK line to the box containing the trouble symptom. Turn to the procedure indicated and continue to follow a single line by analyzing the results of each test step until the required corrective action is determined. Perform the specified corrective action, then repeat the step at which the failure was encountered.
 C.  All trouble shooting procedures are based on the assumption that wiring is OK and that electrical power is available. If the corrective action in the procedure does not correct the problem, check wiring using the wiring diagram.
 D.  The CADC self-test trouble shooting procedure is based on an operational test. Completion of this test assures that (1) air data computer computing modules are functioning accurately, (2) interface and failure warning system between computers and air data instruments is operating and (3) air data instruments respond to input signals and have no major internal failures.
 E.  Areas not checked by the operational test are: outputs and interfaces between computers and systems other than air data instruments; accuracy and other modes of operation in the air data instruments; internal computer functions of static source error correction, altitude digital encoder operation, and pressure transducer operation; and two outputs from the total air temperature probes.
 2.  Prepare for Trouble Shooting
____________________________
 A.  Apply airplane power (Ref 24-22-00, Maintenance Practices [Apply Power]).
 B.  Verify that all CADC 1, CADC 2 and all air data instrument circuit breakers on P7 panel are closed.
 C.  Assure autopilot/flight director and auto throttle systems remain off.
 D.  Adjust captain's and first officer's altimeter barometric settings to
 29.92 inches of mercury. Record altimeter readings.
 E.  Verify that all pitot and static probes and ports are vented to
 atmosphere and probe heaters are off.

 EFFECTIVITY

 
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Prepare system for trouble shooting as described in par. 2. Check on front panels of both central air data computers (CADC) that no yellow annunciator lights are lit. IF -

NOT OK
OK ONE OR MORE YELLOW ANNUNCIATOR LIGHTS LIT - Depress and hold SELF-TEST or button A switch until ALT, M, and TAS warning lights go off, then release switch and check that annunciator light is off. When button A is released the ALT light will be on while the computer outputs are slewing. If annunciator is still lit, replace CADC (34-12-01) and perform specified tests.

Place mode select switch on CADC to LAMP CHK position. On CADC P/N 60B00058, depress and hold PUSH-TO-TEST switch and on CADC P/N 60B40126, depress button B and hold, then depress button A and hold. Check that all ALTITUDE REPORTING indicators on front panel come on. IF -

Place STBY-CADC switch on altimeters to CADC position. Depress and hold SELF-TEST or button A switch on CADC and check indicators for response.
(1)  
　
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