COMPONENT MAINTENANCE MANUAL
IN 1502H RADAR INDICATOR
TM109102
1-19
May/01
4. Detailed Theory of Operation
A. Video/RS-170 Module, P/N 8057175-0503 and -0504 (See Figure 6-12.)
The video/RS-170 module contains the indicator on/off circuit, high-speed line receivers
for the TTL inputs from the interface unit, video amplifiers, the degaussing circuit,
brightness circuit, composite video enable circuit and composite video processing
circuitry. The schematic of the video/RS170 module is presented in Figure 6-12.
(1) On/Off Circuit
The on/off circuit consists of transistor Q1001 and associated components. The
emitter of Q1001 is grounded, via pin 12 (IND ON) of rear panel connector P1001,
when the radar system is turned on at the control unit. When the power supply of the
interface unit comes on, it su5 volts to the base of Q1001 via pin 9 of P1001.
This causes QIOOI to switch on, grounding pin 26 (ON/OFF) of P1011. This line is
routed to the low voltage power supply (LVPS) and turns on the indicator power
supply when QIOOI switches on.
Pin 11 of P1001 is a ground connection from the interface unit. This ground is
returned to the interface unit, via relay contacts of K1001A and pin 10 (EN DR) of
P1001, to enable the line drivers which drive the indicator. This interlock arrangement
keeps the interface unit line drivers off when radar is selected if an indicator is not
connected. The contacts of K1001A open to disable the interface unit line drivers
when RS-170 or CCIR video is selected.
(2) Composite Video Enable Circuit
The composite video enable circuit consists of transistor Q1014, relay K1001A, and
associated components. This circuit routes CCIR or RS-170 composite video signals
to the green gun of the CRT when the ENABLE line (P1001-3) is grounded. It also
produces the ENABLE discrete to the composite video processing circuits on the
video/RS170 module and EN output to the sweep module to configure the required
circuits to handle the reception of video inputs from the aircraft. When the ENABLE
line is open, this circuit allows normal radar and NAV overlay presentations to be
displayed on the color indicator.
When the ENABLE line is open, +12 volts is divided down via R1024, R1023 and
Zener diode CRIO08 to approxi4 volts at the base of Q1014, which therefore
conducts. With Q1014 turned on, its collector is essentially grounded. This ground is
applied to pin 9 of relay K1001A and the relay is energized by +5 volts through its coil.
With K1001A energized, the switching contact (pin 2) is connected to normally open
contact pin 3 and normal green video from the interface unit (via the Q1011/Q1012
circuit) is applied to the green gun (KG) of the CRT via pin 6 of connector J1006. As
mentioned, contacts 8 and 7 of relay K1001B are also closed to enable the interface
unit line drivers.
When the ENABLE line is grounded, the base of Q1014 is grounded via CR1007 and
CR1008, and Q1014 is switched off. This removes the path to ground for energizing
the relay coil, and the relay is deenergized. The switching contact from pin 2 now
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