TM 11-6720-242-35
CHAPTER 6
AUXILIARY EQUIPMENT
NOTE
This chapter covers direct support and general support maintenance for Control Panel LA-428A
(V/H panel). It includes instructions for troubleshooting, repairing, and aligning the equipment.
Section I. FUNCTIONING OF THE V/H CONTROL PANEL
6-1. General
follower Q1.
b. The purpose of the regulator circuit is to keep a
constant output of 100.6 vdc at the emitter of Q1. This
The V/H control panel generates dc voltage levels (V/H
voltage is adjusted by potentiometer R4, the V/H
signals) analagous to aircraft velocity over altitude from
calibrate control. VR1 regulates the emitter voltage of
input primary power. It does this by rectifying the
Q2. Diode CR5 provides temperature stability.
incoming 115 vac, regulating the resultant dc voltage,
c. The output of the regulator circuit is applied across
and passing it through a resistive divider network. Any
the voltage divider made up of resistors R6 through
of twelve selected dc levels can be tapped from the
R18. KNOTS PER FOOT switch S2 taps across the
divider network through a rotary switch (the KNOTS
divider network and ground to deliver the selected
PER FOOT switch, S2) located on the faceplate. The
voltage level to the camera. The output signal is
V/H control panel also receives 5 vdc which is used to
applied through pins C and B of connector 4J1.
illuminate the panel edgelights.
6-4. Edgelights
6-2. Power Application and Protection
A five vdc signal is applied to connector 4J3 through
pins L and G of connector 4J1. Terminals El and E2
Primary power at 115 vac, 400 Hz, single phase enters
connect the five vdc input to the plastic faceplate. This
the V/H control panel through connector 4J1-F. The
plate has embedded in it a set of red lamps which light
power side of the line is interrupted by circuit breaker
when power is applied from the camera control. The
CB1, the POWER switch. CB1 is a magnetically
lamps in the plastic plate are not replaceable; the entire
activated time-delay device, which opens from 0.2 to 7
plate must be replaced when the lamps fail.
seconds at an overload of 125% of its 0.5 ampere
rating.
6-5. RFI Suppression
6-3. Generation of V/H Signals
All inputs to and outputs from the V/H control panel pass
a. The incoming ac primary power is impressed across
through noise suppression filter FL1,
electrically
situated at the interface of connector 4J1. Further, the
isolation transformer T1, including approximately 105
V/H control panel cover butts against an rf filter gasket
vac in its secondary. This, in turn, is applied to the
material cemented to the panel face.
bridge rectifier made up of CR1 through CR4. Capacitor
C1 filters the output of the rectifier (about 150 vdc),
which is applied across the series-shunt regulator made
up of transistor Q2, zener diode VR1, and emitter
6-1
