Bg Board - Sony BVM-1916 Operation And Maintenance Manual

3-2. BG BOARD
3-2-1. Luminance Signal Circuit
Filter SW
ICl 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
G)
and pin© , also pin
(D
and pin®.
Input signal: eTo,
Delayed signal by delay line: e,1
Second delayed signal: en
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 DLl.
+Vee
e-ro
et =
(ero
+ en)/2
Therefore eo is
DLI
-Vee
Figure 4
eo = -(er1 +Jt(er1 --½(ero +er2)))
1st term
2nd term
K: variable constant
05
+Vee
R
eo
07
R
-Vee
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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A
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8
-lf--
-eo
Figure 5
Y Delay, Y Buffer Amplifier
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
(B-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 transistor<; 023 and IC'3.
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 AMPLIFIER. 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 IC'6 (2/3) and is made sampling by IC'6
(3/3). Amplitude of AGC pulse and DC' voltage supplied from
CHROMA control on the front panel are compared and mach-
ed by lC7 (1/2) with controlling the above gain control amplifier.
This control voltage is supplied to the control terminals of R-Y and
B-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 B-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 CP14-CP19, transistor 029, Q30,
Q39, Q40, Q49, Q50 and IC5. CP14-CP19 perform matrixing and
IC5 works as a switch.
3-2-5. COMPONENT R-Y Amplifier and Delay Circuit
R-Y signal of COMPONENT signal is compensated with amplitude,
porality and delay time to match the R-Y signal of decoder output.
BLOCK DIAGRAM OF BG BOARD
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0,Y,QUT
lAPT.VR
KILLER
FILTE:R SW
COMP IN
Y.IN
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CL.P.SW
W.CL. P
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RGB. SW
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COLOR VR
R·V IN
S.S.N
S.S.P
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8-Y IN
C, R·Y.OUT
MATRIX SW
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V R-V. OUT
I? 0.G·Y, OUT
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BG (
COLOR GAIN CONTROL, COMPONENT R-\' AMP&. DELA\')
APERUTURE CONTROL,\' DELA\'
I. 8·\ OUT
0 8-Y.
OUT
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