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Circuit Description
1. POWER
SUPPLY
The
power
supply
circuit
of
the
AAl
- A
chassis
is
comprises
a
primary
rectifier
smoothing
circuit,
an
oscillation
circuit, a control circuit and an output rectifier
circuit.
The AC input voltage
is rectified at the double or full-wave
rectifier smoothing
circuit, and an unstable
DC voltage
is
generated
at both terminals
of the smoothing
capacitor
C307.
The double
or full-wave
rectifier circuit is build by
switching the triac on or off in IC501
cSTR81
145A>.
This
voltage
is supplied
to the
oscillation
circuit,
which
is
composed
of a blocking oscillator circuit that switches the
switching transistor Q313 ON and OFF.
A square-wave
oscillation
is generated
in the
input
winding
according
to operation
of the control
circuit.
A
quare-wave
with amplitude dependent
on the turns ratio of
the input and output windings
is obtained
in the output
winding. This is rectified in the output rectifier circuit, and
the desired DC voltage is produced.
2. IF&
DEFLECTION
(TDA8361/8362)
The IF output signal from the tuner passes through
the
SAW filter, and it is input to pins
45
and
46ofIC101.
Within
the
IC, the
IF signal
passes
through
the
IF
amplifier, video detection
and video amplifier circuits, and
is outputted from pin 7 as a composite
video signal. In the
monaural
model,
this
composite
video
signal
passes
through
the 5.5 MHz(B/G)
/ 6. OMHZ(I) / 6.5 MHz(D/K)
/
4.5 MHz(M)
sound
bandpass
filtering
circuit,
and
it is
inputted into pin5 of IC101. In the stereo model, the SIF
signal is supplied
from pin 14 of IC181 <TDA2546A>
to
pin 5 of IC101 through
the sound
bandpass
circuit for
modulation
of the main carrier. In the IC1 01, this sound IF
signal
passes
through
the SIF amplifier,
FM detector,
external
audio switch and audio output circuit, and it is
then outputted from pin
50
as audio drive signal (Monaural
model). In the stereo model, the main audio signal is fed
from pinl to the stereo controllerIC(MC44131
PB).
The video signals applied to pins 13 or 15 are separated
into vertical-
and horizontal-
sync. signals respectively
by
the sync. separator in the IC.
The horizontal
oscillator
requires no external components
and is fully integrated.
This oscillator
is always
running
when the start - pin 36 is supplied
with 8V, and the
horizontal
drive signal is outputted from pin 37. VR401 is
used for horizontal centring adjustment.
The
separated
vertical
sync.
signal
from
the
sync.
separation
circuit passes through the vertical - separation
circuit, and is applied to trigger divider circuit.
The horizontal
oscillation
pulse and vertical
sync. pulse
are monitored
by the trigger divider circuit to select either
the 50Hz or 60Hz system,
and automatically
adjust
vertical amplitude.
The output
signal from the trigger
divider
triggers
the
the
vertical
oscillator
circuit
whose
external
timing
-
components
consist
of R402, C401 to pin 42, and the
vertical ramp signal is outputted from pin 43. VR451
is for
controlling
the amount of AC feedback
applied to pin
41
for adjustment
of the vertical amplitude.
3. VIDEO
CHROMA
(TDA8361/8362)
The
composite
video signal output from the pin
7ofIC101,
passes through
Q1 22, and the sound traps X124, Xl 25,
X126, X127 to reject the sound
carrier
components,
is
then
supplied
to pin 13 through
the equalizing
circuit
consisting
of Q1 35, Q132 and Q1 34. The external
video
signal from SCART
or other AV terminals
is supplied
to
pin 15.
The video signal input to pin 13 or pin 15 is separated
into
luminance
(Y) signal and chroma signal in ICI 01. These
pins are also common to the H/V- sync. separation
circuit
input already described.
-
The peaking of Y signal is adjusted
by DC voltage on pin
14.(''SHARPNESS"
control)
The chroma signal is divided into R-Y
and B-Y
chroma
signals, which are demodulated
and output from pin 30 (R
- Y) and pin 31 (B - Y). These
chroma
signals
pass
through
the 1H delay line circuit
(IC270),
and are re -
inputted at pin 29 (R-Y)
and pin 28 (B-Y).
These R-Y/B-
Y signals
pass through
the RGB matrix circuit and the
RGB selector
circuit of IC1 01. The internal
RGB signals
are generated
in the RGB matrix circuit
and the RGB
selector,
consisting
of
linear
amplifiers,
clamps
and
selects
either the internal
RGB signals
or the external
RGB signals input from pin 22 (R) , pin 23 (G), pin 24 (B).
Selection
is controlled
by the voltage
at the RGB switch
control (pin 21) and mixed RGB modes are possible since
the RGB switching is fast.
The RGB switch also functions
as a fast blanking
pin by
_
blanking
the
RGB
output
stages;
here
internal
and
external RGB signals are overruled.
The
RGB
signals
for
the
on -
screen
display
are
superimposed
onto the selected
RGB signals at the base
of transistors
Q21 O, Q211 and Q212 respectively.
The saturation
of colour
gain is controlled
by the DC
voltage of pin 26. ("COLOUR"
control)
The contrast control voltage present at pin 25, controls the
-
RGB
signal
gain,
and
the
brightness
control
voltage
present at pin 17, controls DC level of RGB signals.
The
RGB
signals
are
finally
buffered
before
being
presented
to the RGB output pins [pin 20 (R), pin 19 (G),
pin 18 (B)].
–4–
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