Intercom Control Circuit. As shown in figure 3-2, the
intercom circuit receives CREW CALL control inputs at connector pins
J7-C, J8-R, and J3-A. When any input is a low (logic 0) signal,
current flows through diode TB1CR1 or TB1CR2 to provide a low to
external system equipment at connector pin J3-C.
In addition, the
following functions occur:
Relay K1 operates when the COCKPIT CREW CALL TRIGGER
input goes low. Contacts K1-A2 and K1-A1 close to connect the
interphone audio signal at connector pin J7-J to contact B2 of relay
K2. Contacts K1-B2 and K1-B1 close to activate relay K3. Contacts
K3-A2 and K3-A1 connect the flasher lamp control return input at con-
nector pin J7-B to external system equipment at connector pin J7-A.
Relay K2 operates when the CREW CALL TRIG or CREW CALL
input is low. Contacts K2-A2 and K2-A3 open, and contacts K2-A2 and
K2-A1 close. This connects the interphone audio signal at connector
pin J7-J to external system equipment at connector pins J6-e and J2-L
and removes the terminating resistor TB1R1 from the signal line.
Contacts K2-B2 and K2-B3 open to break the override audio signal path
between contact K1-A1 and connector pins J2-M and J6-g.
On indicator CCA A3, the output of timer U1A goes high
(logic 1) when any CREW CALL input goes low. The output of timer U1A
The 5 ( 1) Hz output pulse of
resets multivibrator U1B.
multivibrator (U1B) is applied through transistor Q8 to operate relay
K3. Contacts K3-A2 and K3-A1 close to provide the flasher lamp
control output to external system equipment at connector pin J7-A.
The 5 (1) Hz pulse also passes to external system equipment at
connector pin J8-P. After five to seven seconds, the timer output
goes low, multivibrator U1B is inhibited, and relay K3 restores.
Monitor Circuits. As shown in figure 3-3, terminal board
TB2 and diodes CR5 and CR6 receive transmitter control and plain text
input from external system equipment at connector pin J6-T. The
logic 0 input also causes a low signal through diode TB2CR2 and
connector pin J6-m to external system equipment. When relay TB2K1
operates, contacts A2 and A1 close to connect the PLAIN TEXT FM
signal at connector pin J7-U to diode A3CR5 and to external system
equipment at connector pin J7-G. When the PLAIN TEXT FM signal is a
logic 0, the PLAIN TEXT FM outputs are also low at connector pins
The PLAIN TEXT UHF monitor circuit is a direct link
J8-G and J7-G.
to the system with no separate controls such as relay K1 to affect
its operation. When a logic 0 is input to connector pin J7-H, diode
CR6 is forward biased placing the logic 0 on connector pin J8-L.
When a logic 1 is placed on connector pin J7-H, diode CR6 is reverse
biased and connector pin J8-L becomes a logic 1.