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Receiver-transmitter Unit, Power Supply Control Unit and Battery Supply Unit Functional
TM-9-1240-369-34 Range Finder Fire Control: (Laser) AN/VVG-1 (1240-00-470-2156) Manual
Reply gating card (operational circuits)
TM 9-1240-369-34
(1) Power supply control unit.  The power supply
The gate also ensures the system is not in the test
mode, because it is not desired that the laser actually be
unit consists of the following circuits; PFN charge power
fired during routine testing. If these conditions are all
supply, low voltage power supply, --1600 V power supply.
met, the fire signal is developed. The fire logic applies a
reply gating, select logic, counters, interface circuits,
turnoff signal to the PFN control logic to inhibit PFN
preregulator, and a pulse forming network. Each circuit
charging during the time the laser is fired, and a charged
is explained in the following paragraphs.
(a) PFA charge power supply module.  The
signal to the range light flasher logic. Prior to firing, the
reset flip-flop causes that logic circuit to apply range light
PFN charge power supply is a plug-in module which
signals to the red RANGE backlights so that they are
draws a constant current from the power source during
continuously on.  When the charged signal is applied
the PFN charge cycle and, after the energy storage
with the manual reset signal, it opens a gate for the
capacitors in the PFN are charged, provides a repeaking
range light oscillator so that the backlights will flash.
operation to maintain the voltage until the laser is fired.
This indicates that the laser is ready to fire. After firing, a
The charging cycle is controlled by a linear amplifying
reset signal developed in the transmitter logic circuit card
charging sense circuit that includes a multivibrator and
assembly resets the charge logic flip-flop.  It cannot
four amplifiers. This circuit develops a pulsating, rather
operate subsequently until the reset flip-flop has been
than a continuous. recharging cycle. PFN voltage adjust
reset by the SCR trigger signal, generated with the firing
(R 10) enables field adjustment of the PFN voltage and,
of the flashtube, so that it can accept the manual reset
consequently, the energy that may be stored in the PFN.
signal generated by pressing the RESET switch, or the
If R10 is set for too high an energy level. the laser flash
manual reset that occurs when the system is turned on.
can be intense enough to severely damage the
The PFN charge power supply also develops +400 V
transmitting optics; if set too low, insufficient energy will
from the + 1600 V supply for the flashtube trigger circuit.
be directed on the target to permit detection by the
(b) Bias power supply cards.  A DC to DC
receiver. A thermistor is provided in this circuit to correct
converter in the preregulator converts the prime power
the PFN voltage for laser temperature changes. A high
from the battery power supply unit to + 15 V. The + 1.5
voltage DC to AC converter functions as a regenerative
V is then applied to a regulator whose output is + 10 V.
oscillator. developing a square-wave output that turns
A DC to DC converter in the low voltage power supply
two power transistors on and off to provide a constant
utilizes a square-loop oscillator to develop + 5, --5. and
current PFN charging and repeaking function. The PFN,
+ 29 V from the + 15 V output to the preregulator. Only
consisting of capacitors and inductors is charged to
the +5 V output of the low voltage power supply is
about + 1200 V. It provides the current and voltage to
regulated. The -1600 V power supply converts the + 15
maintain the desired duration of flashtube firing. Power
V regulated voltage to -1600 V required for the
supply protection is provided by a circuit that utilizes a
photomultiplier tube (PMT) bias network.  DC to DC
differential amplifier and silicon controlled rectifier to
conversion. with a driven squarewave generator and full-
prevent excessive current in the power drive by turning it
wave rectification, develops these voltages.
off before the end of half cycle. or in the event of a short
(c) Reply gating card (test circuits).  Data
in the PFN. The circuit also detects high overvoltage
processing begins in the reply gating circuit card
transients and cuts off the power drive to prevent
assembly. Some of the circuitry on this card is devoted
excessive collector voltage buildup. Further protection is
exclusively to test circuits.  With the LASER MODE
provided  by  a  differential  amplifier  that  senses
CONTROL switch set to TEST, the laser cannot be fired.
overvoltage and acts through the PFN control logic circuit
Built-in test circuits in the reply gating card allow
to cause the SCR to cut off the power drive. .A dump
simulated range signals to be processed to verify the
relay forms a discharge path for the PFN when power is
various logic elements.  Pressing the R/T control unit
removed from the receiver/transmitter unit. to eliminate
RANGE switch in test mode simulates firing and
the safety hazard of a residual charge. Activation of the
processing of one, two, three, or four replies, which are
RANGE switch on the R/T control unit initiates the firing
displayed on the commander's unit RANGE (METERS)
of the laser. The range signal is applied to the fire logic
and RETURNS indicators.  The simulation logic test
which contains a flip-flop driven by the
circuitry on the reply gating card develops simulated
multivibrator in the charging sense circuit. and a gate to
video, simulated A-trigger, and simulated reset signals
determine that the PFN is charged, the system has been
manually reset, and the RANGE switch is being pressed.

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