CIRCUIT DESCRIPTION
1. POWER SUPPLYcontrol) The chroma signal is divided into R-Y and B-Y
The power supply circuit of the EB4-A chassis ischroma signals, demodulated in IC201, and output from
composed of a rectifier smoothing circuit, an oscillationpin30 (R-Y) and pin31 (B-Y). These chroma signals pass
circuit, a control circuit and an output rectifier circuit. Thethrough the 1H delay line circuit (IC271), and they are
AC input voltage is full-wave rectified by the rectifierinput to pin29 (R-Y) and pin28 (B-Y). These R-Y/B-Y
smoothing circuit, and an unstable DC voltage issignals pass through RGB matrix circuit and RGB
generated at both terminals of the smoothing capacitorselector circuit of IC101. The internal RGB signals are
C607. This voltage is input to the oscillation circuit. Thegenerated in RGB matrix circuit and the RGB selector,
oscillation circuit is provided with a blocking oscillatorconsisting linear amplifiers, clamps and selects either the
circuit that switches the switching transistor Q613 ONinternal RGB signals or the external RGB signals input
and OFF, and an oscillation frequency and a duty squarefrom pin22(R), pin23(G), pin24(B). Selection is controlled
wave pulse are generated in the input windingsby the voltage at the RGB switch control (pin21) and
according to operation of the control circuit. A square-mixed RGB modes are possible since RGB switching is
wave pulse whose size is dependent on the turn ratio offast. The RGB switch also functions as a fast blanking
the input and output windings is obtained in the outputpin by blanking the RGB output stages; here internal and
winding. This is rectified in the output rectifier circuit, andexternal RGB signals are overruled. The colour gain is
the desired DC voltage is obtained.controlled by DC voltage of pin26. (OCOLOUR� control)
The contrast control voltage present at pin25, and the
2. IF & DEFLECTION (TDA8361)brightness control voltage present at pin17 controls DC
The IF output signal from the tuner passes through thelevel of RGB signals. The RGB signals are finally
SAW filter, and it is input to pin45 and pin46 of IC201.buffered before being available at the RGB output pins
The signal input to the IC passes through the IF[pin20 (R), pin19 (G), pin18 (R)].
amplifier, video detection and video amplifier circuits and
is output from pin7 as a composite video signal. And4. AUDIO OUTPUT(TDA7263M)
after this signal is converted to impedance at Q151,The audio signals output from the audio unit are input to
supplies to the video and chroma amplifier stages. pin1(L) and 5(R) of IC171 and passes through the pre-
The sync.-separation circuit separates the video signalsamplifier circuit and drive circuit, after which it is input to
applied to pin13(internal video signal) or pin15(externalthe audio amplifier. The audio amplifier is an SEPP
video signal) to vertical- and horizontal-sync. signals(single-ended, push-pull) OTL type and output to pin8(R)
respectively. The horizontal oscillator requires noand 10(L) to directly drive the speakers.
external components and is fully integrated. The
oscillator is always running when the start-pin36 is5. VERTICAL OUTPUT (LA7832/LA7832)
supplied with 8V. Horizontal drive signal is output fromAn IC (LA7832/LA7833) is used for the vertical output
pin37. VR361 is for adjustment of the horizontal centring.circuit in this chassis. The vertical drive pulse from pin43
The separated vertical-sync. signal from sync. separationof IC201 is input to pin4 of IC501. This pulse drives
circuit passes through the vertical-separation circuit, andIC501, and vertical scanning is performed. In the first half
applied to trigger divider circuit. The horizontal oscillationof scanning a deflecting current is output from pin2 and
pulse and input vertical sync. pulse are monitored by thepasses through the following path:
trigger divider circuit, and switching 50Hz and 60HzVcc(B4) Ţ D501 Ţ pin3 Ţ pin2 Ţ DY Ţ C512 Ţ
system, the vertical amplitude automatically adjusted forVR501/R509. An electric charge is then stored in C512.
50Hz and 60Hz. The output signal from the triggerIn the last half of scanning the current path is C512 Ţ
divider is triggered vertical oscillation circuit consisting ofDY Ţ pin2 Ţ pin1 Ţ VR501/R509 Ţ C512. In this way,
C351, R352 and pin42, and vertical drive pulse is outputan amplifying sawtooth waveform current flows directly to
from pin43. VR501 is for changing the amount of ACDY to perform electron beam defection. Next, in the first
feedback applied to pin41 and for adjustment of the
vertical amplitude. half of the banking period the vertical drive pulse
suddenly becomes OFF, and in order to reduce the
3. VIDEO CHROMA & R.G.B. (TDA8361)current flowing to DY, the current path becomes as
follows by the inductance of DY:
The composite video signal output from the pin7 ofDY Ţ pin2 Ţ pin1 Ţ VR501/R509 Ţ C512 Ţ DY. Also,
IC101 passes through Q151-Q154, and it is supplied towhen the charge of DY has dissipated, the current path
pin13. The external video signal output from SCART isbecomes Vcc24V Ţ pin6 Ţ pin7 Ţ C502 Ţ pin3 Ţ
supplied to pin15. The video signal input to pin13 or
pin15 is separated to luminance (Y) signal and chromapin2Ţ DY Ţ C512 Ţ VR501/R509, and when the
signal in IC201. These pins are used in common withprescribed current value is reached, the vertical drive
H/V-sync. separation input. The peaking of Y signal ispulse becomes ON. This completes one cycle.
adjusted by DC voltage of pin14. (OSHARPNESS�
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F2VAM |
ACEC
