COMPONENT MAINTENANCE MANUAL
IN 1502H RADAR INDICATOR
TM109102
1-20
May/01
connects to the normally closed contact at pin 4. The composite video signal from the
video amplifier (Q1021/Q1022) now is routed through the relay to the green gun (KG)
of the CRT.
The +5 volts now present at pin 9 of K1001 is routed to the composite video
processing circuits as ENABLE and is inverted by U1008B to produce a signal (EN)
that is routed to the sweep module. These two signals set up the appropriate circuits
to handle and process composite video data. The EN signal is also gated through
U1008D and U1008A to provide a logic-low disabling input to MOSFET driver U1013,
thus disabling the RED, GREEN and BLUE input lines from the interface unit.
Finally, the ENABLE grounded input at P1001-3 is routed to the LVPS via CR1022
and P1011-26 to turn on the power supply and ensure that the indicator is powered on
during composite video operation, even if the radar system (interface unit) is off.
(3) Line Receivers
The inputs from the interface unit (RED, BLUE, GREEN, XRET and YRET) are
buffered by on-board differential line receivers. The XRET and YRET inputs are
handled by high-speed voltage comparators U1004A and U1004B, respectively, while
the video is buffered through U1009. The negative input of each line receiver is biased
at +2.8 volts through voltage divider R1028/RlO29. Inputs from the interface unit are
all active low and drive the positive inputs of the line receivers. When these signals
are not active, the positive input pins of the line receivers arE pulled up to +5 volts,
keeping the outputs high (+5 volts). The RED, GREEN and BLUE video outputs are
converted from TTL to MOS levels by U1013 and applied to the video amplifier
circuits. The XRET and YRET signals are multiplexed with the composite video
horizontal and vertical blank signals and they are forwarded to the sweep module if
radar data is selected for display.
(4) Video Amplifiers
The red, green, and blue video outputs from the line receivers are converted from TTL
to MOS levels and applied to complementary MOS stages which drive the three color
guns at the CRT. The red and blue video amplifiers contain circuitry that enables
adjustment of color balance of the CRT guns. The green video amplifier switches its
output to ground to turn on the green CRT gun. The red and blue video amplifiers
switch to levels set by voltage-to-voltage converters in U1018 (A, B, C, and D),
adjustable using R1047 and R1057. The red video amplifier is described below.
Operation of the green and blue video amplifiers are identical.
The red video output from line receiver U1009 is active low. A high level (+5 volts) is
off, while a low level (0 volts) represents the data. This signal is buffered and inverted
to positive true by TTL-to-MOS driver U1013. The video output from U1013 is on at
+12 volts and off at 0 volts. This signal is coupled through C1017 and C1018 to the
complementary output stage.
The red output (KR) to the CRT, present at TP1011, is switched b65 volts
(-0501) or +53 volts (-0503, -0504) with the gun off and 0 volts with the gun on, by
Q1008 and Q1009, respectively. Use of capacitive coupling between U1013 and the
output stage ensures that both MOS transistors are turned off in the event of loss of
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