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TM 11-820-695-35
When Q1 conducts, its collector voltage is low and
second and third stages of amplifier A2. Registor R25
triggers the 1.1 kHz oscillator into oscillation. When Q1
provides positive bias to operate the MODULE TEST
is not conducting, its collector voltage is high and the
indicator DS1 under zero output conditions. Capacitors
1.1 kHz oscillator cannot oscillate because a high
C6 and C7 are decoupling capacitors for the + 12v and -
voltage is applied through CR10 to the emitter of Q7.
6v supplies. Resistors R14, R15, and R26 through R32
The multivibrator output at the collector of Q2 is applied
are  voltage  dividing  resistors  to  provide  proper
to the 1.6 kHz oscillator circuit on 1A13A5 and
monitoring levels.
alternately turns the oscillator on and off.
The
alternating 1.1/1.6 kHz oscillator outputs are applied
2-52.  Daughter Board No.
2 Assembly 1A13A2
through external circuits and pin M to emitter followers
Circuit Functioning (fig. 5-41)
Q4 and Q5. Resistors RS through R12 are used to bias
emitter followers Q4 and Q5.  The output of Q5 is
Daughter board No.  2 assembly contains the central
applied to speaker amplifier A2 through resistors R13,
alarm monitor, the 1..1 kHz test tone oscillator, and the
R83, and R34.  Capacitor C16 couples the signal to
speaker amplifier circuits. The following subparagraphs
amplifier A2.
C16 is a high frequency bypass.
describe each circuit on daughter board No.
2
Stabilization of the amplifier is accomplished with C18
assembly.
and C19. The output of A2 is connected through C20,
C21 and R36 to speaker amplifier monitor. The output
a. Central Alarm Monitor Circuit. The central alarm
of Q4 is applied to the remote signal alarm through the
monitor circuit monitors the alarm input signals, RCVR
hybrid transformer mounted on orderwire assembly
ALM, XMTR ALM, and PCM ALM. If an alarm condition
1A13.  The 1.1/1.6 kHz audible alarm signal can be
is present at any of the inputs, the central alarm monitor
removed by depressing the RESET pushbutton on
circuit will cause the CNTRL ALARM indicator on meter
meter panel assembly 1A15A8. This removes the path
panel assembly 1A15A8 to change from green to red
through Q3 causing Q3 and the multivibrator to turn off.
and the 1.1/1.6 kHz audible alarm to sound. The alarm
inputs are applied to two OR gates: OR gate A controls
(2) Speaker amplifier A2 receives additional
the 1.1/1.6 kHz audible alarm and OR gate B controls
order-wire inputs through pin 8, speaker volume control
the CNTRL ALARM indicator on meter panel assembly
No. 1 input. The signals are amplified for application to
1A15A8.
the speaker on meter panel assembly 1A15A8. A circuit
diagram of amplifier A2 (integrated circuit MC1554G) is
(1) With ground applied to any of the alarm
provided in figure 24.
inputs, OR gate A  (diodes CR6-CR9, resistors R18-
R21, and capacitors C5-C8) detects an alarm condition
(3) With ground applied to any of the alarm
and controls the audible alarm circuits.  Assume that
inputs, OR gate ,B (diodes CR2-CR5 and resistors R14-
ground is applied to pin 6 (PCM ALM) causing capacitor
R17) detects the summary alarm condition and causes
C5 to discharge through resistor R18.  The negative
the CNTRL ALARM indicator on meter panel assembly
pulse developed across R18 is coupled through diode
1A15A8 to change from green to red.  Assume that
CR6 to the cathode of silicon controlled switch Q3
ground is applied to pin 6 (PCM ALM) causing diode
causing Q3 to operate. With Q3 operating, a ground
CR2 to conduct. With CR2 conducting, transistor switch
return is connected to the emitters of multivibrator
Q6 is turned-off.  For this condition, the operating
transistors Q1 and Q2 permitting the multivibrator to
voltage for the green lamp, CNTRL ALM-NORMAL, is
operate. R4 and C2 determine one time constant of the
removed from pin P, and the ground return for the red
multivibrator and R3 and C1 determine the other time
lamp, CNTRL ALARM, is applied to pin N through CR2.
constant. R2 and R5 are collector bias resistors of the
Thus, the CNTRL ALARM indication on meter panel
multivibrator. When pin 4 of Q3 is connected to + 12v
assembly 1A15A8 changes from green to red (alarm
through pins E and A and R6, the current to turn on Q3
condition).
is from +12v through R1 and R7 to ground. CR1 is used
as a bias diode. With the multivibrator operating, the
1.1 kHz and 1.6 kHz oscillators are alternately turned on
b. 1.1 kHz Oscillator Circuit. The 1.1 kHz oscillator
and off. The multivibrator output at the collector of Q1
circuit generates the 1.1 kHz signal which is used for
is applied to the emitter of Q7 (part 2-90 of 1.1 kHz
test
tone
and
part
of
the
audible
oscillator circuit) through diode CR10.
2-90


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