7.  Removal/Installation of Lavatory Loudspeaker (Fig. 405)
A.  Remove Loudspeaker
(1)  
Release two quick-release fasteners near each inboard corner of ceiling PSU in lavatory or insert small rod through hole in each inboard corner and push to release latches as applicable and lower PSU.

(2)  
Identify and detach two leads from speaker.

(3)  
Remove four screws, speaker cover, and speaker.

B.  Install Loudspeaker
(1)  
Hold speaker and cover in place and secure with four screws.

(2)  
Attach leads to speaker.

(3)  
Raise PSU and check that latches are fully engaged.

8.  Test Loudspeaker Installation
A.  Close PA AMPLIFIER circuit breaker on P6.
B.  Provide electrical power and energize buses on P6.
C.  Press the call button at a PSU and check that a single high tone is heard from the speaker.

D.  If a more definitive test of speaker output is desired, perform Passenger Address System -Maintenance Practices (Ref 23-31-0).
E.  Remove electrical power if no longer required.
5C8 
23-31-11 Page 404  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Jun 20/85 

532  PSU Loudspeaker Installation (ATI Interior) 
Feb 20/85  Figure 403  23-31-11 
Page 405 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

H59590
Typical Lavatory Loudspeaker Installation  518 
23-31-11  Figure 405  Feb 15/79 
Page 406 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

INTERPHONE SYSTEMS - DESCRIPTION
1.  General
A.  The service interphone system contains facilities which enable voice communication between the cabin attendants and between the attendants and the crewmembers in the flight compartment. In addition, the system provides the means for voice communication between those stations provided to facilitate ground servicing operations.
B.  The flight and ground crew call system is used in conjunction with the service interphone system to signal personnel at these stations to use the interphone system to communicate with the calling party.
C.  Electrical power for the systems is provided through circuit breakers on panels P6-2 and P18-4.
557 23-40-0 May 01/76 Page 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

SERVICE INTERPHONE SYSTEM - DESCRIPTION AND OPERATION
1. General
A.  The service interphone system provides ground crew personnel and all airplane crewmembers with facilities that enable two-way voice communications during airplane servicing or during normal flight operations. The location of components is shown on Fig. 1 and 2.
B.  Handset jacks are located throughout the airplane, internally and externally, for use by ground crew personnel to facilitate airplane servicing and maintenance. The service interphone switch on pilots' overhead panel P5 is used to disconnect these jacks from the system when they are not in use.
C.  Handsets are installed on the forward and aft attendants' panel to provide facilities for communication between attendants. Control cabin crewmembers gain access to the system by selecting service interphone on their audio selector panels (Ref 23-53-0). This enables two-way voice communications between all crewmembers.
D.  The service interphone system has no on/off switch. The system is energized whenever 28-volt dc power is applied through circuit breaker SERV/ATT INPH AMPL on panel P6-2. A dual power source is provided from the battery bus and unswitched electronics bus-2.
2.  Amplifier
A.  A transistorized amplifier module is installed in the audio accessory unit located on shelf 1 of electronic rack E2. It amplifies input audio sufficiently to provide communication to all service interphone stations.
B.  Design of the amplifier permits a temporary short to occur on either one of the input or output circuits without catastrophic failure of the amplifier. Automatic gain control circuits ensure a constant output regardless of the number of handsets connected to the amplifier. Either carbon or transistorized microphones may be used with the amplifier. The amplifier uses 28-volt dc power and completes the necessary dc voltage to the system microphones.
3.  Handsets
A.  The telephone type handsets are stowed on hangers at the forward and aft attendants' stations. Handset provisions (jack) are installed on the aft face of the pilots' center aisle stand.
545 23-41-0 Nov 01/74 Page 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
　
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