Sony TVP-08, Training Manual

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43
Main Y and C Buffers
Overview
The purpose of the Y and C buffers is to pass the signal from the input
switching circuit to the 3D Comb Filter. While performing this, the circuit
filters out unwanted frequencies above 7 MHz. In addition to these func-
tions, this circuit also separates the horizontal and vertical sync from the
Y or composite video signal.
Y Buffer
The Y or composite signal is passed through Q532, which is the output
buffer for the input switching circuit. It then goes to Q1340, which pro-
vides further buffering for the signal before it enters FL1301. The signal
enters FL1301/2 and exits FL1301/3. FL1301 filters out all unwanted
signals above 7 MHz. After being filtered, the signal goes through an-
other buffer, Q1342. The signal exits Q1342/E and is split to Q1344/B
and Q1334/B. Q1344 provides additional buffering for the signal, which
is then sent through C1491 and to IC1309 ADC. If you try to probe Q1344/
B with a scope, you will load the signal and the picture will become dis-
torted. Q1334 is the input to the sync separator circuit.
Sync Separator
Q1334 is the input to a differential amplifier that consists of Q1334 and
Q1339 and their associated components. While Q1334/B has the Y or
composite signal input to it, Q1339/B is set to a DC reference level of 3.9
volts. The result of these inputs, which is output at Q1339/C, is that only
the sync signals are amplified since they are below the threshold. The
signal leaving Q1339/C contains vertical and horizontal sync pulses. This
signal is applied to Q1337, which acts as a buffer. Next, the signal is
applied to Q1341, which amplifies and inverts the sync signals. Negative
going vertical and horizontal sync signals are output from Q1341/C. This
signal is then sent to IC1306 3D Comb Filter.
C Buffer
The C signal is only present when an S video input is used. The C signal
is passed through Q536, which is the output buffer for the input switching
circuit. It then goes to Q1345, which provides further buffering for the
signal before it enters FL1302. The signal enters FL1302/2 and exits
FL1302/3. FL1302 filters out all unwanted signals above 7 MHz. After
being filtered, the signal goes through another buffer, Q1347. The signal
exits Q1347/E and is split to Q1346/B and Q1336/B. Q1346 provides
additional buffering for the signal, which is then sent through C1433 and
sent to IC1306 3D Comb Filter.