COMPONENT MAINTENANCE MANUAL
IN 1502H RADAR INDICATOR
TM109102
1-26
May/01
(f) RS-170/CCIR Horizontal Position Circuit
A horizontal position circuit on the video/RS-170 module for both RS-170 and
CCIR video operates in conjunction with separate RS-170 and CCIR horizontal
position circuits on-board the sweep module. Together, these circuits are adjusted
to delay the X-retrace pulse as necessary to ensure that the horizontal sweep
does not begin before video is available. One-shot multivibrator U1020A is
triggered by the output from U1021 and generates the active-low XRET signal
from pin 7. This is applied to an input of multiplexer U1003 and is passed to the
sweep module when composite video is selected. Potentiometer R1102, along
with other timing components, R1184 and C1100, establish the XRET pulse width.
One-shot U1020A also produces a positive pulse at pin 6. The width of this pulse
is equal to that of the XRET pulse from pin 7. The trailing (negative-going) edge of
this pulse triggers one-shot U1020B, which produces the positive pulse (from pin
10) that is used to develop the pin 4 square wave input for horizontal processor
U1021.
(g) Horizontal Blank Circuit
One-shot multivibrator U1006B is triggered by the composite sync pulses
separated by sync separator U1005 and produces the DC restore signal to Q1002
which restores the DC component of the video signal. It reinserts the DC
component on the horizontal sync tips to maintain the black level during these
periods. The video signal is sampled during the back porch to obtain an output
that brings the level of the sync tips at TP1003 to the correct level via U1012A.
The leading (negative-going) edge of the horizontal sync pulse from sync
separator U1005 triggers U1006B, which then produces a negative output pulse
at pin 9. The negative pulse from pin 9 of U1006B is applied to horizontal
processor U1021, which generates the X-retrace (XRET) signal, which is routed
off the board through U1012 to the sweep module and high-voltage regulator
module for synchronization purposes. This output is used for DC restoration at
Q1002.
B. Sweep Module (See Figure 6-9 or 6-10.)
(1) Horizontal Position Circuit
The horizontal position circuit delays the X-retrace (XRET) pulse up to approximately
3 microseconds, depending upon potentiometer settings and type of video (radar,
CCIR or RS-170) selected for display, to ensure that the horizontal sweep does not
begin before video is available. Separate horizontal position adjustments are provided
for radar, CCIR and RS-170 video selections.
The horizontal position circuit consists of high speed comparators U2007A and
U2007B, NOR gates in U2006 and associated discrete components. The XRET pulse
is an active-low TTL signal. Between XRET pulses, the negative input to U2007B is
low. With the positive input of U2007B biased at approxi2.4 volts, the output
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