3-2. BG BOARD
3-2-1. Luminance Signal Circuit
Filter SW
!CI works as a selector switch of composite video signal or
luminance signal derived from Y /C separation circuit. This IC
activates by either FILTER-SW in right side drawer or killer signal.
Aperture Control
Aperture control circuit is composed of DLl (delay line), transistors
Q5, 7, 8 and IC2. IC2 operates as a variable resistor. Resistance
value between Pin(DandG)is controlled by the potential between
pin 0 and pin © , also pin (D and pin© .
Input signal: eTo,
Delayed signal by delay line: eT 1
Second delayed signal: e72
See Figure 4
e1 (at base of transistor Q5) is obtained as below due to the com-
bination of direct wave and reflected wave by DLI.
+Vee
+Vee
eo
e-ro
05
-Vee -Vee
Figure 4
e1 = (ero + e72)/2
Therefore eo is
eo = -(m +1[ (eT1 -{ (eTO + e72 )})
1st term
2nd term
K: variable constant
In the above equation, 1st term shows waveform A in Figure 5 and
2nd term shows waveform B. When K is variable,amount of pre·
shoot and overshoot can be varied.
Switch S1 is used for selection of boost frequency.
3-3
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I '
-{Ji-
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I I I
t-
Figure 5
Y Delay, Y Buffer Amplifier
A
B
-eo
Y/C delay time can be matched by delay line DL2 and Y signal
is amplified and fed to the next stage.
3-2-2. Color Gain Control Circuit
In this section (R-Y) signal processing is described as below, but
(8-Y) signal is processed by the same way as (R-Y) signal.
R-Y Amplifier and Clamping
The R-Y color difference signal from the decoder board is amplified
at the amplifier composed of transistors 021 and 022 and clamped
at the Horizontal Sync by transistors Q23, Q24 and IC3.
R-Y Gain Control Amplifiter
This is a variable gain control amplifier composed of variable resistor
element of IC4 and transistors 025-027. Gain of this amplifier can
be controlled by the color gain control voltage at the pin@ of
IC4.
AGC Pulse Generator
Generates the reference pulse for AGC (Automatic Gain Control)
of color gain control circuit.
Gain Control Amplifier for AGC Pulse
Circuit is the same as R-Y GAIN CONTROL AMPLll·IER. Gain of
this amplifier is controlled by the voltage at pin® of IC4.
Color Gain Control
AGC pulse, which is output signal of Gain control amplifier for
AGC pulse, is clamped by IC6 ( 2/3) and is made sampling by 1C6
(3/3). Amplitude of AGC pulse and DC voltage supplied from
CHROMA control on the front panel are compared and mach-
ed by IC7 ( 1/2) with controlling the above gain control amplifier.
This control voltage is supplied to the control terminals of R-Y and
8-Y gain control amplifiers and controls color gain.
3-2-3. G-Y MATRIX amplifier
G-Y signal is obtained by matrixing R-Y signal and 8-Y signal with
the amplifier composed of transistors Q44 and Q45.
3-2-4. NTSC MATRIX SW
NTSC MATRIX mode operation is obtained by the matrix circuit
composed of resistor networks CPI4-CP19, transistor 029, 030,
Q39, Q40, Q49, QSO and IC5. CP14-CP19 perform matrixing and
!CS works as a switch.
I
3-2-5. Vector Output Circuit
3-2-6. COMPONENT R-Y Amplifier and Delay Circuit
R-Y Vector Output Gain Switcher
Vector output levels are compensated for each color standards,
NTSC, PAL and SECAM.
R-Y signal of COMPONENT signal is compensated with amplitude,
porality and delay time to match the R-Y signal of decoder output.
R-Y Vector Output Amplifier and Clamping
Vector output signal is amplified by IC9 (2/2) and transistor Q54
and clamped by IC8 and transistor Q55 for the suitable operation.
BLOCK DIAGRAM OF BG BOARD
-
-
01 ,01
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4
.5MHi S1 FREQ SELECT
05, 7,8, 1(2
DL 2, 09
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8 • Y VECTOR OUT
AMP & DELAY
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FILTER SW
A4
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84
COMP IN
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C.CL.P
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A6
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(COLOR GAIN CONTROL, COMPONENT R-Y AMP 8: DELAYY
APERUTURE CONTROL,Y DELAY,VECTOR OUT
-
-
-
3-4
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