Circuit Description
1. POWER SUPPLY
The power supply circuit of the Ml -Achassis is
comprises aprimary rectifier smoothing circuit, an
oscillation circuit, acontrol 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. This voltage is supplied to the oscillation circuit,
which is composed of ablocking oscillator circuit that
switches the switching transistor Q313 ON and OFF.
Asquare-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 7as acomposite 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 5of IC101 through the sound bandpass circuit for
modulation of the main carrier. In the IC101, 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 controller ICI 103(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 the
vertical amplitude.
The output signal from the trigger divider triggers the
vertical oscillator circuit whose external timing
components consist of R402, C401 to pin 42, and the
w
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 Q122, and the sound traps Xl 24, Xl 25,
X126, X127 to reject the sound carrier components, is
then supplied to pin 13 through the equalizing circuit
consisting of Q135, 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 IC101. These
pins are also common to the H/V- sync. separation circuit
input already described.
The peaking of Ysignal 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 1Hdelay line circuit (IC270), and are re -
inputted at pin 29 (R-Y) and pin 28 (B-Y). These R-Y/B-
Ysignals pass through the RGB matrix circuit and the
RGB selector circuit of IC101. 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 afast 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)].
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