Sony BVP-570, Maintenance Manual

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2-6 (E)
BVP-570
(2) Video Signal System
VA-163A board
The VA-163A board amplifies the video signals output from the OHB and performs the following
processes:
.
Black shading correction
.
Gain-up control
.
Blanking cleaning
. White shading correction
.
Feedback clamping
.
White balancing
.
Flare compensation, and
. Pre-knee
In addition, it also switches between the video signals, TEST SAW(TEST1) signal and 3-STEP
TEST(TEST2) signal.
PR-242 board
The PR-242 board converts the analog R, G, and B video signals into digital signals with the 12-bit A/D
converter having sampling/holding functions.
It generates clocks required for the A/D conversion and the digital process circuit from the clocks gener-
ated by the OHB.
In addition, the PR-242 board adds a linear matrix and detail signals to the analog-to-digital-converted R,
G and B signals.
It performs the processes such as pedestal control, black gamma correction, gamma correction, knee
correction, knee saturation and white clipping for the signals. It also performs the followings.
. Generates an internal color-bar signal and switches between this signal and the main line signals.
. Creates detail and aperture signals from the digital R and G signals.
.
Creates four kinds of skin tone gate signals. (one of them is for skin auto iris)
.
Detects signals for auto white/black balancing, auto hue detection, auto iris and auto knee.
.
Detects black/white shadings, generates a waveform to compensate them and outputs the waveform to
the VA-163A board.
.
Detects the black level and outputs the feedback clamp voltage to the VA-163A board.
.
Generates TEST SAW waveforms and output them to the VA-163A board.
The video signals that have thus been digital-processed, are then converted to the Y, R-Y and B-Y
signals. Some signals are output to the DA-88A board and the others are output via the MB-602 board as
digital video signals output at the same time. The C signal is generated from the R-Y and B-Y signals
with the color encoder IC on the PR-242 board. These Y and C signals are sampled at 36-MHz rate and
quantized by 10 bits to be digital-to-analog converted. The resultants are then output to the DA-88A
board as the monochrome signal for VF or modulated chroma signal. The monochrome signal for VF has
the zebra signal for level indication, character signal and center marker signal on it. In addition, it has the
VF detail signal, which is used to vary the detail level for the above-mentioned monochrome signal,
independently of the detail signal for the main line signals. The wide-band luminance signal is sampled at
36-MHz rate and quantized by 10 bits independently to be digital-to-analog converted. The resultant is
output to the DA-88A board after the blanking cleaning is performed and the SYNC signal is added to
that signal.
2-4. Circuit Description