H20678 K90629
Switched Service Interphone Jacks Location  503 
23-41-0  Figure 1  Aug 15/67 
Page 2 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

5C8  Service Interphone System Component Location 
Jun 20/85  Figure 2  23-41-0 
Page 3 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Service Interphone System Circuit  5C8 
23-41-0  Figure 3  Oct 20/83 
Page 4 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

B.  Each handset has a transistorized preamplifier built into it for amplification of microphone signals. The PTT switch on the handset is used to complete the circuit to the preamplifier. The service interphone amplifier provides the proper voltages for operation of the preamplifier.
4.  Operation (Fig. 3)
A.  Power is applied to the service interphone system through circuit breaker SERV/ATT INPH AMPL on panel P6-2. The system is placed in operation by closing its circuit breaker.
B.  Crewmember handsets are located on the forward and aft attendants' panels. Handsets for the switched service interphone jacks must be supplied by maintenance personnel. Communications between all stations is possible when the SERVICE INTERPHONE switch on the pilots' overhead panel P5 is set to ON. When the switch is set to OFF, only the crewmember handsets are connected to the system.
C.  Microphone signals from all handsets are combined and amplified by the service interphone amplifier. The amplifier output is distributed to the receivers of all handsets.
D.  Control cabin crewmembers gain access to the system by selecting SERV INT on their audio selector panels (Ref 23-53-0). The SERV INT position of the mike selector switch connects the microphones and headphones of the flight interphone system to the service interphone amplifier.
E.  Service interphone audio levels are controlled by two screwdriver adjustment potentiometers located on the front of the audio accessory unit. The amplifier gain potentiometer should be set to provide a suitable listening level at the switched service interphone jacks; then, the interphone level potentiometer should be set to provide a suitable listening level at the crewmember handsets.
545 
Nov 01/74  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  23-41-0 Page 5 

SERVICE INTERPHONE SYSTEM - TROUBLE SHOOTING
1.  General
A.  The service interphone system has the attendants' handsets and control stand handset jack connected directly to the amplifier; failure of the amplifier is indicated if communication between all stations is not available. If only jacks connected through the SERVICE INTERPHONE switch are not operable, then either the switch is faulty or a jack is shorted. Failure of individual jacks or handsets can easily be detected by interchanging handsets between stations.
B.  If the service interphone system is completely inoperable, ensure power is available to the  28 volt dc battery transfer bus or unswitched electronic bus-2 and the service interphone amplifier circuit breaker on load control center P6 is closed. If power is available, replace the audio accessory unit. No terminals are available to check for power to the amplifier.
556 
Feb 01/76  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  23-41-0 Page 101 

SERVICE INTERPHONE SYSTEM -ADJUSTMENT/TEST
1.  Test Service Interphone System
A.  General
(1)  The following test procedures should be conducted whenever a jack, handset, or audio accessory unit has been replaced. When using jacks, wipe handset plugs clean prior to inserting plug into jack as dirt may cause intermittent operation or damage the jack. Handsets must be furnished by ground personnel. Handsets are installed at the attendants' stations.
B.  Prepare to Test
(1)  
Provide ground power to the airplane and energize the buses on load control center P6.

(2)  
Ensure all interphone and DUAL PWR SOURCE circuit breakers are closed.

(3)  
Position the SERVICE INTERPHONE switch to ON.

C.  Test Service Interphone System
(1)  Using a handset at the forward attendant's station, establish satisfactory communications with the following stations:
(a)  
Aft Attendant's Handset

(b)  
Panel P19 SERVICE Jack

(c)  
APU (Auxiliary Power Unit)

(d)  
Right Wheel Wel1

(e)  
Left Wheel Wel1

(f) 
 Right Wing Refueling Station
　
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