Circuit Description - Sanyo C21EF27 Service Manual

CIRCUIT DESCRIPTION

1. POWER SUPPLY
The power supply circuit of the EC5-A chassis is com-
posed 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 smooth-
ing circuit, and an unstable DC voltage is generated at
both terminals of the smoothing capacitor C607. This volt-
age is input to the oscillation circuit. The oscillation circuit
is provided with a blocking oscillator circuit that switches
the switching transistor Q613 ON and OFF, and an oscil-
lation frequency and a duty square wave pulse are gener-
ated in the input windings according to operation of the
control circuit. A square-wave pulse whose size is depen-
dent on the turn ratio of the input and output windings is
obtained in the output winding. This is rectified in the out-
put 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 IC201. 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 sig-
nal is converted to impedance at Q151, supplies to the
video and chroma amplifier stages.
The sync.-separation circuit separates the video signals
applied to pin13(internal video signal) or pin15(external
video signal) 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. VR361 is for
adjustment of the horizontal centring. The separated ver-
tical-sync. signal from sync. separation circuit passes
through the vertical-separation circuit, and applied to trig-
ger 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 trig-
gered vertical oscillation circuit consisting of C351, R356
and pin42, and vertical drive pulse is output from pin43.
VR501 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 IC201
passes through Q151-Q154, and it is supplied to pin13.
The external video signal output from SCART is supplied
to pin15. The video signal input to pin13 or pin15 is sepa-
rated to luminance (Y) signal and chroma signal in IC201.
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 and B-Y chroma signals, demodulated in
Service manual-EC5 chassis
IC201, and output from pin30 (R-Y) and pin31 (B-Y).
These chroma signals pass through the 1H delay line cir-
cuit (IC271), 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 IC201. 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, and the brightness control voltage present at
pin17 controls DC level of RGB signals. The RGB signals
are finally buffered before being available at the RGB out-
put pins [pin20 (R), pin19 (G), pin18 (R)].
4. AUDIO OUTPUT(AN5265)
The audio signal output from pin52 of IC201 is input to
pin2 of IC001 and passes through the pre-amplifier circuit
and drive circuit, after which it is input to the audio ampli-
fier. 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/LA7833)
An IC (LA7832/LA7833) is used for the vertical output cir-
cuit in this chassis. The vertical drive pulse from pin43 of
IC201 is input to pin4 of IC501. This pulse drives IC501,
and vertical scanning is performed. In the first half of
scanning a deflecting current is output from pin2 and
passes through the following path:
Vcc(B4) D501
VR501/R509. An electric charge is then stored in C512. In
the last half of scanning the current path is C512
pin2 pin1 VR501/R509
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 induc-
tance of DY:
DY pin2 pin1
when the charge of DY has dissipated, the current path
becomes Vcc24V
pin2 DY C512
scribed 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
IC201 and switches the drive transistor Q431. This switch-
-5-
pin3 pin2 DY
C512. In this way, an
VR501/R509 C512
pin6 pin7 C502
VR501/R509, and when the pre-
C512
DY
DY. Also,
pin3