VESTEL 11AK19, Руководство по обслуживанию, Страница: 7 / 40

8. VERTICAL OUTPUT STAGE WITH TDA8351/8356
The TDA8351/8356 vertical deflection circuit can be used in 90° and 1 1 0 ° deflection systems with field frequencies from
50 up to 1201-fz. With its bridge configuration the deflection output can be DC coupled with few external components.
Only a single supply voltage for the scan and a second supply for the flyback are needed. The TDA8356 is intended for 90°
systems and the TDA8351 is intended for 1 1 0 ° systems.
The drive voltage is amplified by an amplifier and fed to two amplifiers, one is inverting and the other is a non inverting amplifier.
The outputs (pins 7 and 4) are connected to the series connection of the vertical deflection coil and feedback resistor Rsense
(R702//R703). The voltage across Rsense is fed via pin 9 to correction amplifier, to obtain a deflection current which is proportional
to the drive voltage. The supply voltage for the TDA8351/8356 is 15VDC at pin 3. The supply voltage generator has a separate
supply voltage of 45VDC at pin 6.
9. VIDEO OUTPUT AMPLIFIER TDA6107Q
The TDA6107Q consists of three monolithic video output amplifiers. The amplifier can be seen as an operational amplifier
with negative feedback.
The advantage of negative feedback is that the amplifier characteristics do not play an important role up to certain frequencies.
The internal flash diodes protect the amplifiers against flash over in the picture tube.
The only protections required at the cathode outputs are a flash resistor and a sparkgap.
The TDA6107Q has an internal thermal protection circuit which gives a decrease of the slew rate at high temperatures.
Furthermore, the device needs only one power supply voltage (Vdd).
In contrast to previous types of DMOS video amplifiers, all the external resistors (Rf, Ri and Ra) are integrated, so the gain is fixed
and saves 9 resistors.
Furthermore, the reference voltage is integrated, it saves a resistor divider and a decoupling capacitor. So, the replacement
value of the TDA6107Q is very high.
The TDA6107Q is provided with a black current data pin. Since TDA884X is used as drive device, no adjustments are required
for gain and black setting, as the TDA884X has PC white point adjustment and black current set-up.
10. SINGLE/MULTISTANDARD VIF/SIF-PLL and FM-PLUAM
DEMODULATOR TDA9818
The TDA9818is an 1C for multistandard vision IF signal processing, sound AM and FM demodulation.
It is a gain controlled wide band VIF-amplifier (AC-coupled). It is applicable (or IP frequencies of 38.9 MHz, 45.75 MHz and 58.75 MHz.
True synchronous demodulation is provided with active carrier regeneration. It has a VCO frequency which can be swrtchable
between L and L accent (alignment external) picture carrier frequency.
The TDA9818 has a SIF input for single reference QSS mode (PLL controlled). SIF AGC detector is to provide gain controlled
SIF amplifier. The AM demodulator is without extra reference circuit. The supply voltage is +5VDC at pin 21.
1 1 . COMBFILTER SAA4961
The SAA 4961 is a one-chip, PAL/NTSC combfilter 1C with internal delay lines, filters, clock control, synchronisation and
signal switches. The combfilter function is realised in a switched capacitor technique, so it has time discrete but amplitude
continuous processing.
The Y/CVBS input is first clamped and then fed to the delay-line and combfilter section via a low pass pre-filter
This filter can be bypassed via the external LPF-on pin. This pin is internally pulled up, to put the filter default on. The Y/CVBs
input is also fed to the sync seperator, where horizontal and vertical reference pulses are made.
Bypass mode can be forced via BYP (pin 3).FSC (pin 1 ) is the subcarrier input which is connected to the colour decoder.
Input FSCSW pin indicates if fsc or 2*fsc is used.
The Sys1,2 pins (20, 23) indicate which system standard is processed. Sys2 is internally pulled up, Sys1 is internally pulled down.
Therefore when the Sys1,2 inputs are left open, automatically PAL 4.43MHz is forced.
SAA4961 output pin 1 5 "CVBS" can be used for parallel-synced teletext decoders, to guarantee that the teletext display always
has a correct timing relation with the main picture. Comb filter is disabled by setting SAA4961 pin 3 "BYP" high.
12. POWER SUPPLY (SMPS)
The DC voltages required at various parts of the chassis are provided by an SMPS transformer controlled by the 1C MC44604
which is designed (or driving, controlling and protecting switching transistor of SMPS. The transformer produces 150/115V for
FBT input, ±14V for audio output 1C, S+5V for microcontroller, +15V for vertical output (field scan) and +33V for tuner and some
other ICs and transistors.
13. MICROCONTROLLER SDA525X
The device is TV TEXT tuning and control system based on the SDA 525X TV TEXT microcontroller. It is designed for a low
cost mono TV-SET with analogue picture and sound control. Neverthless the system offers an on screen display (OSD) and
IR remote control of all functions.
SDA525X has the following features:
- Display of program number, channel number, TV standard, analogue values, sleep timer, parental control, and mute is done by OSD.
- Single LED for IR active, standby and on mode indication.
- 1 Control line to select external source.
- 3 Control lines for TV standard selection.
- Frequency synthesis tuning (62.5 kHz steps)
- 1 9 2 step tine tuning
- Channels corresponding to standards B/G, OIRT, L and I (l+)
- Mono sound control by analogue voltage
- System configuration with service mode
14. SERIAL ACCESS CMOS 8K (1024*8) EEPROM ST24C08
The ST24C08 is a 8Kbit electrically erasable programmable memory (EEPROM), organised as 4 blocks of 256'8 bits.
The memory is compatible with the PC standard, two wire serial interface which uses a bi-directional data bus and serial clock.
The memory carries a built-in 4 bit, unique device identification code (1010) corresponding to the PC bus definition.
This is used together with 1 chip enable input (E) so that up to 2*8K devices may be attached to the K; bus and selected individually.