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C. AIRPLANES WITH FIVE CONTROL LIGHTS ON THE SELCAL CONTROL PANEL; The SELCAL system consists of a five channel SELCAL decoder unit and control panel. The component locations are shown on figure 1. The electronic chime is part of the aural warning system (AMM 31-26-00).
D. The SELCAL system consists of a five channel SELCAL decoder unit and control panel. The component locations are shown on figure 1. The electronic chime is part of the aural warning system (Ref 31-26-00).
E. 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 the VHF or HF communication system and sent to the SELCAL decoder unit. If the four-tone code received is identical to the SELCAL code assigned to the airplane, the flight crew will be signaled by SELCAL lights and an electronic chime. The flight crew can reset the light and chime with the appropriate reset button on the SELCAL control panel.
F. SELCAL system No. 1 obtains 28v dc from switched electronic power bus No. 1 on load control center P18. SELCAL system No. 2 obtains 28v dc from switched electronic power bus No. 2 on load control center P6.
Control Panel
_____________
A. Two indicator lights and a PUSH-TO-RESET switch are located on the control panel. SELCAL-1 indicator light comes on when decoder-1 is activated. SELCAL-2 indicator light comes on when decoder-2 is activated. When pushed, the PUSH-TO-RESET switch deactivates both decoders simultaneously.
B. The SELCAL control panel is installed in the forward electronics control
panel P9.Aural Warning Module
____________________
A. The SELCAL system uses an electronic chime contained in the aural warning module. (Ref Chapter 31, Aural Warning and Call Devices). The chime is connected to both decoder-1 and decoder-2 oscillator relays and will operate when either decoder unit receives the proper combination of tones from the connected radio communication transceivers. The chime will sound a repeating chime each time the decoder is activated.
B. The aural warning module is installed on the right side of the forward electronics control stand.
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A 737-300/400/500MAINTENANCE MANUAL
AURAL WARNING MODULE
F40530
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A 737-300/400/500MAINTENANCE MANUAL
NO. 1 DECODER SELECTOR KNOBS
NO. 2 DECODER SELECTOR KNOBS
NA-134D2
N1401
DUAL SELCAL DECODER
CODE
FIVE CHANNEL SELCAL DECODER
DISPLAY
WINDOW
CODE
SELECT
CODE SELECTOR KNOB (EXAMPLE)
SELCAL System Component Location
Figure 1 (Sheet 2)
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A05707
A 737-300/400/500MAINTENANCE MANUAL
4. SELCAL Decoder
______________
A. The SELCAL decoder is a five-channel multiplexed unit; the three VHF transceivers provide the audio inputs to the first three channels. The HF-1 transceiver provides the audio input to channel four. Channel five is not used. Each channel has compressor amplifiers, a selector, filters and latching circuits.
(1)
Every channel will recognize the unique four-tone code assigned to the airplane. The assigned code is pin programmable and determined by airplane wiring to SELCAL decoder connector D2555B.
(2)
The four tone code is resolved with a 16-bit binary word. Four bits of the word determine each tone. A coding receptacle is wired to implement the unique 16 bits of this code for the airplane. This receptacle is mounted external to the SELCAL decoder and connected to it with a short cable. Thus the SELCAL decoder can be replaced without affecting the code. The coding receptacle is placed on the rack behind the decoder. The cable has provisions for seventeen wires. The first wire provides a common ground and is always installed. The other wires are installed at each position where a low bit (0) is required and deleted where a high bit (1) is required.
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