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7.0 - OPERATION DESCRIPTION TELEVISION SET CIRCUIT
Fig.1- Block diagram
3.Tuner
4. AV
switches
1. Power Supply
The block diagram in Fig.1 shows how the TV set circuit works divided into 8 basic circuits.
7.1 - POWER SUPPLY
IC901, IC902, IC903, T901, Q901 and surrounding components (9xx)
This is a switching mode power supply designed to operate in AC power source from 99 Volts to 242 Volts
and 50/60 Hertz.
The main device is the TDA16846 (controller for switching mode power supplies).
There are two different operating modes, low power standby and full operation mode.
-Standby: The power supply works in the burst mode and the circuit turn-on during 2 ms and turn-off
during 12 ms. In this mode the power consumption is less than 2 Watts in 120 V AC and less than 3 Watts in
220 V AC. In the burst mode, the output voltages are reduced to 10% of the normal values (except
microprocessor supply voltage) .
-Full operation mode: This mode is activate by the microprocessor (Remote control or front panel). The
output voltages regulation is controlled by the IC903 circuit, opto coupler feedback (IC902) and by the IC901.
The basic output voltages are:
1. 108/128 Volts (CR14300_20300/CR20310_29411) to horizontal circuit;
2. +12 and –12 Volts to audio and vertical circuits;
3. 9 Volts to TV signal processor, stereo decoder and AV circuits;
4. 5 Volts to microprocessor and memory circuits;
5. 3.3 Volts to microprocessor and front panel switches circuits.
There are 3 basic protection mode:
1. AC power source undervoltage: the power supply will turn-off when the AC source is less than 95 Volts.
2. Power consumption limit: when the power consumption exceed 20% of the normal value.
3. Overvoltage outputs shutdown: when the output voltages exceed 15% of the normal values.
7.2 - TV SIGNAL PROCESSOR + MICROPROCESSOR
IC101, IC102 and surrounding components (1xx)
The main device is the TDA9380 (TV signal processor-Teletext decoder with embedded Micro-Controller)
that combines the functions of a TV signal processor together with a Micro Controller and Closed Caption
decoder. The highlights of this device are:
2. TV signal processor
and Microprocessor
Circuit
31
5. Stereo
6.Audio
decoder
output
7.Video
output
8.Horizontal
and vertical
deflections
Speaker
CRT
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