Circuit Operation Description; Board - Sony DXC-390 Service Manual

3-1. VA-193 Board
The VA-193 board consists of the circuit blocks described
below.
. S/H, AGC Circuit and Pre-amplifier
(Main circuit : CXA1757R)
. Processing circuit
. Shading correcting circuit
. Signal generator circuit for lens control
(1) S/H, AGC Circuit and Pre-amplifier
(Main circuit : CXA1757R)
In CXA1757R (IC901), RGB signal that is input from
the PA-236 board, is separated signal using correlative
double sampling processing. There is sampling-hold by
input XSHD and XSHP sampling pulses, is processed.
The separated signal is amplified by a AGC amplifier.
This AGC amplifier can control gain by voltage.
This voltage is input from IC902, is changed by every
gain mode.
The signal that is through the AGC amplifier, is input
to the pre-amplifier circuit. In the pre-amplifier, gives
a gain to R-channel and B-channel signals, suppresses
sensitive uneven between RGB. After that, is output
from IC901 via blanking process and clamp circuit.
The black output level is approximately 1.8V.
(2) Processing Circuit
The RGB signal that is output from IC901 eliminates
the 14 MHz component by the trap filter after through
the buffer. After that, it is input to the white-balance
amplifier (from IC910 to IC912).
This amplifier can be controlled a gain by a voltage
(VCA), VCA gain of R-channel and B-channel is con-
trolled by a voltage giving from IC906 and the white-
balance processing is performed.
And VCA of G-channel is given the signal for com-
pensation from the shading compensation circuit, it is
performed compensation by controlling a gain of G-
channel. The signal after performing white-balance,
after through a pre-knee circuit and a white-clip
circuit, is clamped OPB part by the feedback clamp
circuit (from IC915 to IC918) to approximately 2.1
Vdc, is output to the DP-313 board.
DXC-390/390P
Section 3

Circuit Operation Description

(3) Shading Compensation Circuit
(4) Lens Control Signal Generator circuit
3-2. DP-313 Board
The DP-313 board consists of the circuit blocks described
below.
V-periodic delta wave is generated, it uses the voltage
for VCA gain control, so that shading compensation
function is realized.
The generated delta wave is adjusted so that the wave
center will be around the center on the screen.
The delta wave slant, central adjustment value, offset
adjustment value and delta wave generating on/off are
set in IC903 and IC906.
Signals for controlled lens iris, focus and zoom are
generated. About iris, the signals for video servo and
DC control are alternated (IC913). The video servo
signal makes the Y-signal from the RGB signal of
previous AGC in IC901 and is input to VCA (IC907)
via gain amplifier and clamp circuit. This VCA sets a
gain according to convergence level from IC903. The
control signal for DC control, that is set voltage in
IC903, is output after adjusted gain. The voltage range
of the signal is approximately from 2.5 V to 7.5 V. The
ZOOM and FOCUS control signals are the same set
voltage in IC903, are output after adjusted gain. The
voltage range is the same approximately from 2.5 V to
7.5 V. A voltage of IC903 is controlled from a micro-
processor, and then a lens is controlled.
. A/D converter circuit for video signal
. Around CXD9117R
. CXD9087R and its surrounding circuits
. D/A converter circuit for video signal
. Clock phase control circuit
3-1 (E)