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Circuit Description
1. POWER SUPPLY
The
power
supply
circuit
of the
A7 - A
chassis
is
composed
of a rectifier
smoothing
circuit,
an oscillation
circuit, a control circuit and an output rectifier circuit.
The AC input voltage is full- wave rectified by the rectifier
smoothing
circuit,
and
an
unstable
DC
voltage
is
generated
at both terminals
of the smoothing
capacitor
C507. This voltage
is input to the oscillation
circuit. The
oscillation
circuit
is provided
with a blocking
oscillator
circuit that switches the switching transistor
Q513 ON and
OFF, and an oscillation
frequency
and a duty square
wave pulse are generated
in the input windings according
to operation
of the control circuit. A square-
wave pulse
whose size is dependent
on the turn 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 obtained.
2.IF & DEFLECTION
The IF output signal from the tuner passes through
the
SAW filter, and it is input to pin45 and pin46 of IC1OI.
The signal input to the IC passes through the IF amplifier,
video detection
and video amplifier
circuits and is output
from pin7 as a composite video signal.
And after this signal is converted
to impedance
at Q1 24,
supplies to the video and chroma amplifier stages passed
through the AV switching circuit of IC290.
The
output
signal
from
pin7
passes
through
the
5.5MHz(B/G)/6.0
MHz(l)/6.5MHz(D/K)/4
.5 MHz(M)
filtering
circuit, and it is input to pin5 of ICI 01. The signal input to
the IC passes
through
the SIF amplifier,
FM detector,
external
audio switch and audio output circuit, and it is
then output from pin50 as audio drive signal.
The sync. - separation
circuit separates
the video signals
applied to pinl 3 or pinl 5 to vertical-
and horizontal-sync.
signals respectively.
The horizontal
oscillator
requires no external components
and is fully integrated.
The oscillator
is always
running
when the start- pin36 is supplied with 8V.
Horizontal
drive signal is output from pin37. VR401 is for
adjustment
of the horizontal centering,
The separated
vertical sync. signal from sync. separation
circuit passes through the vertical - separation
circuit, and
applied to trigger divider circuit.
The horizontal
oscillation
pulse and input vertical
sync.
pulse are monitored
by the trigger
divider
circuit,
and
switching
50Hz and 60Hz system, the vertical amplitude
automatically
adjusted for 50Hz and 60Hz.
The output
signal
from the trigger
divider
is triggered
vertical
oscillation
circuit
consisting
of R401 ,C402
and
pin42,
and
vertical
drive
pulse
is output
from
pin43.
VR451 is for changing the amount of AC feedback applied
to pin41 and for adjustment
of the vertical amplitude.
3.VIDEO CHROMA
%.
The composite
video signal output from the pin7 of IC101
passes through
Q1 22/ Q1 24, and it is supplied to pinl 3.
The external video signal output from SCART or other AV
terminal passes through IC290, and it is supplied to pinl 5.
The video signal input to pin13 or pin15 is separated
to
luminance
(Y) signal and chroma signal in IC1 01. These
pins are used in common
with H/V - sync.
separation
input.
The
peaking
of Y signal
is adjusted
by DC voltage
of
pin14.(''SHARPNESS
control)
The chroma
signal is divided
into R - Y, B - Y chroma
signals, demodulated
in IC1 01,
and output from pin30 (R - Y) and pin31 (B- Y). These
"
chroma
signals
pass through
the 1H delay
line circuit
(IC270), and they are input to pin29 (R- Y) and pin28 ( B-
Y). These R- Y/B-
Y signals pass through
RGB matrix
circuit
and RGB selector
circuit
of IC1 01. The internal
RGB signals are generated
in RGB matrix circuit and the
"
RGB selector,
consisting
linear
amplifiers,
clamps
and
selects
either the internal
RGB signals
or the external
RGB signals input from pin22 (R) , pin23 (G), pin24 (B).
Selection
is controlled
by the voltage
at the RGB switch
control (pin21 ) and mixed RGB modes are possible since
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 colour
gain is controlled
by DC voltage
of pin26.
("COLOUR"
control)
The contrast control voltage present at pin25, controls the
RGB
signal
gain,
and
the
brightness
control
voltage
present at pinl 7 controls DC level of RGB signals.
The
RGB
signals
are
finally
buffered
before
being
available
at the RGB output pins [ pin20 (R), pin19 (G),
pin18 (B)].
-/
4.AUDIO OUTPUT
The audio signal output from pin50 of ICI 01 is input to
pin2ofIC171
and passes through the pre - amplifier circuit
and drive
circuit,
after
which
amplifier. The audio amplifier is
Push Pull) type and output to
speaker.
it is input
to the audio
an SEPP (Single-
Ended
pin8 to directly
drive the
–4–
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