Circuit Description; Power Supply - Sanyo C25EG92F Service Manual

CIRCUIT DESCRIPTION

1.POWER SUPPLY

The power supply circuit of the EC3-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 (TDA8362)
The IF output signal from the tuner passes through the
SAW filter, and it is input to pin45 and pin46 of IC101.
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. This
signal is supplied to the video and chroma amplifier
stages through the buffer of Q131.
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. VR401 is for adjustment of the horizontal centring.
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 triggers the oscillation of vertical oscillation circuit
consisting of C401, R402 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 & R.G.B. (TDA8362 )
The composite video signal output from the pin7 of
IC101 passes through Q131 to Q134, 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 separated to luminance (Y) signal and chroma
signal in IC101. 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 IC101, 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 IC101. 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 at pin25, and the brightness
control voltage at pin17 control DC level of RGB signals.
The RGB signals are finally buffered before being
available at the RGB output pins [pin20 (R), pin19 (G),
pin18 (R)].
4.AUDIO OUTPUT(AN5265)
The audio signal output from pin50 of IC101 is input to
pin2 of IC171 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 IC101
is input to pin4 of IC451. This pulse drives IC451, 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) D451
VR431/R459. An electric charge is then stored in C461.
In the last half of scanning the current path is C461
DY pin2 pin1
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 pin1
when the charge of DY has dissipated, the current path
becomes Vcc24V
pin2 DY C461
prescribed current value is reached, the vertical drive
pulse becomes ON. This completes one cycle.
-4-
pin3 pin2 DY
VR431/R459 C461. In this way,
VR431/R459 C461
pin6 pin7 C452
VR431/R459, and when the
C461
DY. Also,
pin3