Tv Signal Processor Tda8362A - Grundig CUC 7303 Serviceanleitung

CUC 7303

3. TV Signal Processor TDA8362A

3.1 Overview:
With this TV design the whole signal processing is carried out in a
single IC, i.e. the TV Signal Processor TDA 8362A.
It accommodates the following stages:
IF Signal:
- IF amplifier
- Demodulator
- AFC
- AGC
- Coincidence identification
CCVS Signal:
- Signal source switch for the CCVS signal
- Luminance processing
- Colour demodulation
- Chrominance processing
- Colour contrast control
- RGB matrix
- C-AV input
- Signal source switch for RGB signals
- Brightness control
- Contrast control
- Black level control (cut-off)
Sound:
- Signal source switch for the sound
- Sound demodulation
- Volume control
Deflection:
- Sync separator
- Line oscillator
- ϕ1 phase control
- ϕ2 phase control
- Trigger pulse generation for the line output stage
- Line counter
- Saw-tooth generation for the vertical deflection
- Drive signal for the field output stage
Dependent on the associated circuitry, the IC is also able to process
PAL, NTSC and SECAM signals.
3.2 IF
The IF spectrum of frequencies is fed through a symmetrical path from
the tuner Pins 11 and 10 via the filter F901 and the Surface Acoustic
Wave filter F906. The signal formed by the Surface Acoustic Wave filter
is applied symmetrically to Pins 45 and 46 of the signal processor. The
demodulation of the CCVS signal is carried out in a product demodulator.
Bild-ZF und Demodulation
Vision IF and Demodulation
für denTuner
for the Tuner
vom Prozessor
from Processor
Koinzidenz
Coincidence
GRUNDIG Service
45
ZF vom Tuner
IF from Tuner
46
~
U
47
~
U RV
49
9
AFC
4
The required demodulator circuit F130 is connected to Pin 2 and Pin 3.
The demodulated signal passes through an amplifier and is then
present at Pin 7 of the IC (BB). The IC identifies the synchronising
signal internally and for this reason, feedback of the line flyback pulse
for gating purposes is not necessary. Corresponding to the synchron-
ising signal level a control voltage is generated. This control voltage
first acts on the controlled input amplifier of the IF. Via Pin 49 a
reference threshold U
amplifier of the IF is regulated. If the threshold is exceeded, the control
voltage U is applied from Pin 47 to the tuner. Pin 47 is an open collector
t
output. In uncontrolled condition, the voltage is approximately 5V. With
increasing input amplitude the AGC level decreases. The direct
voltage for automatic frequency control (AFC) is generated in the
demodulator. Pin 9 feeds out this signal as a current signal. When the
received frequency increases the control voltage for AFC decreases.
The processor IC850 evaluates the signal and fine tunes the tuner
accordingly. The demodulated signal is examined by the sync detector
for the presence of synchronising signals. If no such signals are
present, the IC150-(4) switches to "Low". By this level the processor
IC850-(33) can identify that the coincidence signal is missing and
mutes the sound.
3.3 CCVS Signal
The demodulated CCVS signal leaves IC150-(7), TDA8362A, as a
baseband signal together with the sound-IF. In the following path, the
sound signal is separated from the CCVS signal. After the transistor
CT921 and the sound trap F923 and F924 the signal path divides.
Via the transistor CT110 and IC2807 (optionally) it is fed through to the
videotext decoder IC850-(30) as FBAS
CT963, CT962 it is supplied to the Scart socket pin 19.
At the signal source switch IC150-(13), the signal is present as CCVS.
The second input of the signal source switch Pin 15 is connected to the
Scart socket pin 20.
At IC150-(16), the processor IC850-(42), voltage U
decides as to whether the signal from the tuner or the external signal
is processed.
3.4 External CCVS Signal
At the signal source switch IC150-(15) either an external CCVS signal
from the Scart socket or the RF-CCVS signal is present. The voltage
U at IC150-(16) decides which signal shall be passed on, the CCVS
VQ
signal from the Scart socket or else the RF-CCVS signal. IC150-(16)
"Low", the internal signal is selected; IC150-(16) "High", the external
signal is passed on.
Attention: If the option "Decoder On" has been selected the TV
expects the signal to come from the Scart socket. However the CCVS
signal from the tuner can be measured at output Pin 19 of the Scart
socket.
F130
2 3
TDA8362A
Schaltungsbeschreibung / Circuit Description
is set. Below this threshold, only the input
RV
signal, and via the transistors
SC
, transistor CT840
VQ
FBAS- und Ton-
7
Ausgang
CCVS and Sound
Output
Sync
Detector
2 - 9