23-28-00
 ALL  ú ú 05 Page 8 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 F.  When the ground station operator wants to call a specific airplane using the SELCAL system, he uses the four-tone code which has been assigned to the airplane. The transmitted code is received by a communication system and sent to the SELCAL decoder unit. If the four-tone code received is identical to the code assigned to the airplane, the flight crew will be signaled by the SELCAL light and electronic chime. The flight crew can reset the light and chime by pushing the PUSH-TO-RESET button on the SELCAL control panel.
 G.  AIRPLANES WITH N1401 DECODER; The received audio from the communication transceivers is amplified by the compression amplifier and applied to the active filters. An active filter will pass the amplified signal if the frequency of the signal matches the specified frequency of the filter. The output of each filter is parallel-bus fed to each of the four demultiplexers.
 H.  Pushing the PUSH-TO-RESET button deactivates the latch, which causes the chimes to stop and the SELCAL indicator light to turn off. The system is again ready to accept the next audio signal.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 23-28-00
 ALL  ú ú 11 Page 9 ú Nov 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 SELCAL SYSTEM - TROUBLE SHOOTING
________________________________
 1.  General_______
 A.  AIRPLANES WITH A NA134-D2 DECODER; the decoder is mounted on shelf No. 2 of electronic equipment rack E2.
 B.  AIRPLANES WITH A N1401 DECODER; the decoder is mounted on shelf No. 3 of electronic equipment rack E1.
 C.  Since both SELCAL decoder units are housed in a single case, failure of either SELCAL system requires that the entire SELCAL decoder unit be replaced in the electronic equipment rack. The SELCAL indicator light comes on and the chime sounds when a SELCAL transmission is received. To verify whether the decoder is receiving the tones, the tones may be monitored with the flight interphone system headphones and associated communication system. If the chime sounds but the light does not come on, replace the control panel. If the light comes on but the chime does not sound, reference Aural Warning System - TS (31-26-00/101) for trouble shooting of Aural Warning System faults. If the light does not come on and the chime does not sound when SELCAL tones are received, replace the decoder.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 23-28-00
 ALL  ú ú 07 Page 101 ú Jul 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 SELCAL SYSTEM - ADJUSTMENT/TEST
_______________________________
 1.  General
_______
 A.  The test that follows will do a test for the correct operation of the SELCAL components. These components operate when you receive a signal from the applicable communications system.
 B.  Make sure of the airplanes location. See that there are no objects in the path of the signal between the control tower and the airplane.
 TASK 23-28-00-705-007
 2.  SELCAL System Test
__________________
 A.  Equipment
 (1)  SELCAL Control Tower Encoder - Motorola Model N1304A, N1000A, N1001A or equivalent.
 NOTE: The N1304A encoder provides 16 tones (A through S) and the
____ N1000A and N1001A provides 12 tones (A through M).
 B.  References
 (1)  
24-22-00/201, Manual Control

 (2)  
23-21-00/501, VHF Communication System

 (3)  
23-11-00/501, HF Communication System

 C.  Access
 (1)  Location Zone
 101/102 Control Cabin

 D.  Procedure
　
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