Circuit Description; Video Circuit - Sony UP-890CE Service Manual

UP-890CE/890MD
SECTION 5
CIRCUIT DESCRIPTION
5-1. VIDEO CIRCUIT
5-1-1. Operation
A composite video signal is input from the BNC connector(CN1-(VIDEO-IN)) to the
MA-19 board. The composite video signal is terminated with 75 ohms by R1 and
R2 when the DIP switch (S302-@2) is set to ON. The signal then passes through
the input buffer and branches into three routes. Two of these three signals are input
through trap circuit 1 (FL1 for NTSC signal) and trap circuit 2 (FL2 for PAL
signal) to the analog switch (IC2-@X5)) and selected in accordance with the NTSC or
PAL judgment of a microcomputer. The automatically selected signal and the signal
supplied directly to the input buffer are input to the analog switch (IC2-@@®). An
original signal is selected when the DIP switch (S302-@) is set to ON. A luminance
signal (Y signal) from which the color subcarrier signal has been extracted by the
trap circuit is selected when it is set to OFF. The selected signal is input through
the buffer to IC1-@%.
1C1(1) extracts the C sync signal, (2) emphasizes the picture, and (3) adjusts the
contrast. The extracted C sync signal is output from IC1-@. The degree of the
picture emphasis does not change because the value of the DC voltage input to IC
1-@ is fixed. The signal gain is controlled by changing the DC voltage value at IC
1-@ with the CONT control on the front panel. The gain of the video signal output
from IC1-@ is adjusted with RV1. The dither signal output from IC103-Q@® is injected
into the gain-adjusted signal. The signal is then band-limited using a low-pass filter
and passed through the clamping circuit. The clamp level at that time is determined
by RV2 and the BRT control on the front panel.
The video signal is then input to the analog-digital converter (IC3-Q2) and converted
into 6-bit digital data.
The sampling clock for the analog-digital converter is the 18.432 MHz clock output
from IC103-@. The converted digital data is sent to frame memory (IC104) and digital-
analog converter IC4 and reconverted into analog data. The resultant signal is output
from IC4-©. Since this signal lacks a sync signal, the sync signal is injected by analog
switch IC2. An original signal supplied directly to CN1-(VIDEO IN) is output from
CN1-(VIDEO OUT).
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Fig.5-1. Video Signal Processing Section Block Diagram
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