S 865-068

 (49)
 Make sure the NOSE A/G DISAGREE, AIR/GND DISAGREE, NOSE A/G SYS, and AIR/GND SYS messages do not show on the EICAS.

 S 965-054

 (50)
 Install or remove the switch actuators or deactuators on the proximity sensors as shown below: ~............................................................ | SENSOR | LOCATION | ACTUATOR | DEACTUATOR | .............................................................. | S10067 | Nose Gear | Remove | - -| 2.........…................…..............…..................1

 S 965-055

 (51)
 Use a volt/ohmmeter to measure the voltage between pins 6 (+ voltage) and 12 (ground). The connectors to be measured are in column A of Tables 1 and 2. The measured voltage of each connector must be the same as the voltage shown in column B of Table 1 and column C1 of Table 2.

 S 865-056

 (52)
 Make sure the NOSE A/G DISAGREE is shown on the EICAS.

 (53)
 Make sure the NOSE A/G SYS message shows on the EICAS.

 S 865-057

 (54)
 Move the EICAS computer select switch to the R position.

 (a)
Make sure the NOSE A/G DISAGREE message is shown on the EICAS.

 S 865-069
 

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757 MAINTENANCE MANUAL
 (b)  
Make sure the NOSE A/G SYS message shows on the EICAS.

 G.
Put the Airplane Back to Its Usual Condition

 S 095-058
 (1)  
Remove all the actuators and the deactuators.

 S 445-062

 (2)  
Put the safety-sensitive systems back to their initial conditions (Ref 32-09-02/201).

 S 865-060

 (3)  
Make sure the control lever for the landing gear is in the DN position.

 S 865-061

 (4)  
Remove the electrical power if it is not necessary
 (Ref 24-22-00/201).

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 PROXIMITY SWITCH SYSTEM - DESCRIPTION AND OPERATION
___________________________________________________
 1.  General (Fig. 1)
_______
 A.  The proximity switch system consists of a proximity switch electronics unit (PSEU) and numerous proximity sensors mounted throughout the airplane. The sensors provide position sensing for landing gear, doors and thrust reversers, and basically involves the following subsystems:
 Landing gear systems (systems 1 and 2) (Ref 32-09-02 and 32-61-00)
 Cargo door control system (Ref 52-34-00)
 Door system (Ref 52-71-00)
 Thrust reverser auto restow (left and right) (Ref 78-34-00)
 Thrust reverser indication (left and right) (Ref 78-36-00)

 B.  The sensors sense the proximity of targets installed and provide position signals to the PSEU. Discrete operational inputs to the PSEU include mechanical switches which represent system command or position sensing signal. The PSEU converts all these inputs into output signals for operation and control of relays, lamps and other electronics.

Proximity Switch System
Figure 1

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 C.  The system incorporates built-in-test equipment (BITE) in the PSEU to provide both in-flight testing and on-ground system trouble shooting. BITE tests on a malfunctioning PSEU produce a fault code which indicates the faulty sensor or target state, card, or absence of section operating voltage.
　
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