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CIRCUIT DESCRIPTION
1.POWER SUPPLY
The power supply circuit of the EC2-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
C307. This voltage is input to the oscillation circuit. The
oscillation circuit is provided with a blocking
oscillator
circuit that switches the switching transistor Q313 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 (TDA8361)
The IF output signal from the tuner passes through the
SAW filter, and it is input to pin45 and pin46 of 1C101.
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 Q122, supplies to the
video and chroma amplifier stages. The output signal
from pin7 passes through the 6.0MH2z(I)/5.5MHz(B/G)
trap circuit of X151, and it is input to pin5 of 1C101. 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 pint3 or pin15 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 C401, R402 and pin42,
and vertical drive pulse is output from pin43. VR431 is for
changing the amount of AC feedback applied to pin41
and for adjustment of the vertical amplitude.
3.VIDEO CHROMA & R.G.B. (TDA8361)
The composite video signal output from the pin7 of
IC101 passes through Q122/Q124,
and it is supplied to
pini3. The external video signal output from SCART
is
supplied to piniS. The video signal input to pin13 or
pints is separated to luminance (Y) signal and chroma
signal in 1C101. These pins are used in common
with
H/V-sync. separation input. The peaking of Y signal is
adjusted by DC voltage of pini4. ("SHARPNESS"
control) The chroma signal is divided into R-Y and B-Y
chroma signals, demodulated in 1C101, 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 1C101. 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 OSD signal from
pin23(G). In this stage, the OSD signal which is switched
by blanking signal from pin21 is superimposed
into
internal RGB signals.The colour gain is controlled by DC
voltage of pin26. ("COLOUR?"
control) The contrast
control voltage present at pin25, and the brightness
control voltage present at pint7 controls DC level of RGB
signals. The RGB signals are finally buffered before
being available at the RGB output pins [pin20 (R), pini9
(G), pin18 (R)].
4.AUDIO OUTPUT(AN5265)
The audio signal output from pin50 of IC101 is input to
pin2 of 1C171 and passes through the pre-amplifier circuit
and drive circuit, after which it is input to the audio
amplifier. The audio amplifier is an SEPP (single-ended,
push-pull) OTL type and output to pin8 to directly drive
the speaker.
5.VERTICAL OUTPUT (LA7832)
An IC (LA7832) is used for the vertical output circuit in
this chassis. The vertical drive pulse from pin43 of 10101
is input to pin4 of 1C451. This pulse drives 1C451, and
vertical scanning
is performed.
In the first half of
scanning a deflecting current is output from pin2 and
passes through the following path:
Vcec(B4) —~ D451
—
pin3 > pin2 —
DY ~
C461
—
VR431/R459. An electric charge is then stored in C461.
In the last half of scanning the current path is C461 — DY
— pin2 — pint ~ VR431/R459 — C461. In this way, an
amplifying sawtooth waveform current flows directly to
DY to perform electron beam defection. Next, in the first
half of the banking
period the vertical drive pulse
suddenly becomes
OFF, and in order to reduce the
current flowing to DY, the current path becomes
as
follows by the inductance of DY:
DY — pin2 — pint — VR431/R459 — C461 — DY. Also,
when the charge of DY has dissipated, the current path
becomes
Vcc24V —
pin6 — pin7 — C452 -+ pin3 >
pin2-
DY —
C461
—
VR431/R459,
and when
the
prescribed current value is reached, the vertical drive
pulse becomes ON. This completes one cycle.
6.HORIZONTAL OUTPUT
A horizontal oscillation signal is output from pin37 of
1C101
and switches the drive transistor Q431. This
switching signal is current amplified by the drive
transformer T431 and drives the output transistor Q432.
When Q432 becomes ON, an amplifying current flows
directly to DY through C441/442 - DY —
0432 — GND,
-4-
ar
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