Functional block diagram of Television with explanation
Different stages of television: - The main stages of black and white television are as follows.
Power supply stage:- Here 230 volt power supply is converted to 110 volt and 12 volt DC supply required for different sections (stages) of TV. Following type of power supply are used in TVs and many other electronics items.
1 Transformer power supply:- Consist of a step down transformer with 110 volt 12 volt and 6.3 volt secondary windings. Bridge rectifier and filter capacitor is used to produce 110 volt DC and 12 v DC. 110 volt DC is used in EHT section and 12 volt DC is used in sound section.
2 Scr based power supply:- scr (silicon controlled rectifier also known as thyristor is used to make 110 volt DC regulated supply. 110 volt DC is given to EHT section. All other supply are produced from the EHT section.
3 SMPS POWER SUPPLY :-Now a days all TVs uses smps (switch mode power supply) power supply. More are less are electronic item uses smps power supply. Nearly 30 percent problems of TVs are due power supply and can be fixed by repairing power supply.
Tuner section :- This is the first section of TV. It has three sub section ie RF amplifier section, local oscillator section and a mixer section. It generates local oscillator frequency as per the requirement of receiving RF signal frequency. TV signal received from antenna is given to RF amplifier section with matching transformer known as balloon. The antenna output impedance is 300 ohms to be matched with tuner input impedance of 75 ohms. Balloon is used with input impedance 300 ohms and output impedance 75 ohms as impedance matching transformer between antenna and tuner. The RF signal is amplified in RF amplifier section. Then local oscillator signal and RF signal is mixed in mixer stage. The mixer stage output signal is known as video IF signal which is then sent as input signal to video IF section. AGC (Automatic gain control signal) voltage is received from VIF Section to tuner section for RF Amplifier gain control .12 V DC power supply is given to tuner for its working. In old TVs 12 channel tuner were used in which channel was changed with knob manually. Now a days all TVs are using electronic tuner in which band selection and tuning is done electronically from front panel or remote control. In electronic tuner 33 volt supply is also given as tuning voltage. In electronic tuner varactor diode is used in oscillator circuit to control the oscillator frequency by changing tuning voltage applied to varactor diode. Varactor diode capacitance is changes with reversed bais applied voltage changes.
VIF Section:- This section has a 3 stage video IF amplifier, keyed AGC generator and demodulator built in a single IC . The video IF signal received from tuner is amplified. After amplification VIF signal is demodulated, After demodulation composite video signal is sent to video amplifier and sync separator stage. Sound IF signal is sent to sound IF section.To produce keyed AGC VIF section receive's fly back pulses from EHT section.
Sound IF amplifier:- In this section sound IF signal is amplified in two stages and the signal is demodulated to produce sound or audio signal. Audio signal a sent to audio amplifier stage through volume control.
Sound amplifier :- This section consist of four stages of audio amplification ie first audio amplifier, second audio amplifier, driver stage and. Power amplification stage. All stages of audio amplifier are built in a single IC known as sound/audio amplifier IC. The speaker is connected to output of audio amplifier and convert amplified audio signal to sound.
Picture tube:- The function of picture tube is to produce picture. It has a cathode which is heated by filament. When cathode is heated electrons emits from cathode. With the help of control grid focusing anode, first accelerating anode and final accelerating anode an electron beam is produced and focused at the center of screen. The screen has phosphor coating in side when this electron beam strikes on screen a light spot is produced on screen. With the help of vertical deflection coil and horizontal deflection coil this spot is deflected in sequentially way to create raster. And hence complete screen gets illuminated with a single point of light running very fast on screen . Due to persistence of vision our eyes feels continuous presence of light. The picture formation and raster details will be covered in other article.The video signal from video amplifier is given to cathode of picture tube. It is known as cathode modulation. It control the intensity of spot on screen. The movement of spot created by electron gun is synchronized with the scanning gun of camera so the position of spot and intensity of spot is exactly the same as the camera so same image is formed on the screen. Such 25 images (50 frames) per second is produced by picture tube so that we see a movie picture on screen.
Video amplifier :- The video signal received after demodulation is amplified in video amplifier stage. The output signal is given to cathode of picture tube from the collector of video amplifier transistor. Vertical blanking pulses are also added in this stage for blanking of vertical retrace lines. In color TV video amplifier stage has a chroma IC which processes the composite video signal and produces 3 signal for red, green and blue color. These color signal are amplified in three amplifier transistors and given to red gun (red cathode), green gun and blue gun of color picture tube.
Horizontal oscillator stage:- In this stage horizontal oscillator signal of 15625 hz is generated. A sync separator circuit in side IC separates vertical sync pulses and horizontal sync pulses from composite video signal received from VIF section. A AFC circuit synchronized the horizontal oscillator with horizontal sync pulses. Vertical sync pulses are sent to vertical oscillator for synchronization.
Horizontal driver :- horizontal oscillator signal is amplified in driver stage. A driver transformer is used. The signal from secondary of driver transformer is given to base of horizontal output transistor. The collector supply to the output transistor is received from primary winding of EHT transformer. horizontal deflection Coils are connected to output of horizontal output section.
Horizontal output section:- It uses a power transistor (BU205, BU208), A EHT transformer and horizontal deflection coil placed in yoke which is mounted on picture tube neck. EHT transformer has few more winding which are used to generate 50 volt supply for vertical stage. 6.3 volt winding for picture tube(CRT) filament. Different EHT have some difference in auxiliary supply voltages.
Vertical stage:- This stage has in built vertical oscillator and vertical amplifier in a single IC. Vertical oscillator generate 50 hz saw tooth wave signal. After amplification this voltage is given to vertical deflection coil placed in yoke. The vertical oscillator uses vertical sync pulses received from sync separator to get synchronised with composite video signal. Vertical stage has two presets to adjust vertical hold of picture and vertical linearity of picture respectively.
Some common faults.
No light no sound :- problem of power supply.
Horizontal line:- problem in vertical stage.
No picture no sound but raster (light) is present :- fault is in VIF stage or in tuner stage.
Picture coming sound is not coming:- problem is in sound IF stage or audio amplifier stage.
Sound is OK but only plain light on screen :- problem in video amplifier stage.
Sound OK but no light : problem may be in horizontal oscillator or EHT section.
It is a very brief discription of black and white TV. Interested reader need to go for more details. Any question are welcome in comment. Thanks for reading.
three-phase-welding-rectifier circuit diagram with working principle
main-sections-of-lcd-tv/ LCD TV block diagram
Different stages of television: - The main stages of black and white television are as follows.
Power supply stage:- Here 230 volt power supply is converted to 110 volt and 12 volt DC supply required for different sections (stages) of TV. Following type of power supply are used in TVs and many other electronics items.
1 Transformer power supply:- Consist of a step down transformer with 110 volt 12 volt and 6.3 volt secondary windings. Bridge rectifier and filter capacitor is used to produce 110 volt DC and 12 v DC. 110 volt DC is used in EHT section and 12 volt DC is used in sound section.
2 Scr based power supply:- scr (silicon controlled rectifier also known as thyristor is used to make 110 volt DC regulated supply. 110 volt DC is given to EHT section. All other supply are produced from the EHT section.
3 SMPS POWER SUPPLY :-Now a days all TVs uses smps (switch mode power supply) power supply. More are less are electronic item uses smps power supply. Nearly 30 percent problems of TVs are due power supply and can be fixed by repairing power supply.
Tuner section :- This is the first section of TV. It has three sub section ie RF amplifier section, local oscillator section and a mixer section. It generates local oscillator frequency as per the requirement of receiving RF signal frequency. TV signal received from antenna is given to RF amplifier section with matching transformer known as balloon. The antenna output impedance is 300 ohms to be matched with tuner input impedance of 75 ohms. Balloon is used with input impedance 300 ohms and output impedance 75 ohms as impedance matching transformer between antenna and tuner. The RF signal is amplified in RF amplifier section. Then local oscillator signal and RF signal is mixed in mixer stage. The mixer stage output signal is known as video IF signal which is then sent as input signal to video IF section. AGC (Automatic gain control signal) voltage is received from VIF Section to tuner section for RF Amplifier gain control .12 V DC power supply is given to tuner for its working. In old TVs 12 channel tuner were used in which channel was changed with knob manually. Now a days all TVs are using electronic tuner in which band selection and tuning is done electronically from front panel or remote control. In electronic tuner 33 volt supply is also given as tuning voltage. In electronic tuner varactor diode is used in oscillator circuit to control the oscillator frequency by changing tuning voltage applied to varactor diode. Varactor diode capacitance is changes with reversed bais applied voltage changes.
VIF Section:- This section has a 3 stage video IF amplifier, keyed AGC generator and demodulator built in a single IC . The video IF signal received from tuner is amplified. After amplification VIF signal is demodulated, After demodulation composite video signal is sent to video amplifier and sync separator stage. Sound IF signal is sent to sound IF section.To produce keyed AGC VIF section receive's fly back pulses from EHT section.
Sound IF amplifier:- In this section sound IF signal is amplified in two stages and the signal is demodulated to produce sound or audio signal. Audio signal a sent to audio amplifier stage through volume control.
Sound amplifier :- This section consist of four stages of audio amplification ie first audio amplifier, second audio amplifier, driver stage and. Power amplification stage. All stages of audio amplifier are built in a single IC known as sound/audio amplifier IC. The speaker is connected to output of audio amplifier and convert amplified audio signal to sound.
Picture tube:- The function of picture tube is to produce picture. It has a cathode which is heated by filament. When cathode is heated electrons emits from cathode. With the help of control grid focusing anode, first accelerating anode and final accelerating anode an electron beam is produced and focused at the center of screen. The screen has phosphor coating in side when this electron beam strikes on screen a light spot is produced on screen. With the help of vertical deflection coil and horizontal deflection coil this spot is deflected in sequentially way to create raster. And hence complete screen gets illuminated with a single point of light running very fast on screen . Due to persistence of vision our eyes feels continuous presence of light. The picture formation and raster details will be covered in other article.The video signal from video amplifier is given to cathode of picture tube. It is known as cathode modulation. It control the intensity of spot on screen. The movement of spot created by electron gun is synchronized with the scanning gun of camera so the position of spot and intensity of spot is exactly the same as the camera so same image is formed on the screen. Such 25 images (50 frames) per second is produced by picture tube so that we see a movie picture on screen.
Video amplifier :- The video signal received after demodulation is amplified in video amplifier stage. The output signal is given to cathode of picture tube from the collector of video amplifier transistor. Vertical blanking pulses are also added in this stage for blanking of vertical retrace lines. In color TV video amplifier stage has a chroma IC which processes the composite video signal and produces 3 signal for red, green and blue color. These color signal are amplified in three amplifier transistors and given to red gun (red cathode), green gun and blue gun of color picture tube.
Horizontal oscillator stage:- In this stage horizontal oscillator signal of 15625 hz is generated. A sync separator circuit in side IC separates vertical sync pulses and horizontal sync pulses from composite video signal received from VIF section. A AFC circuit synchronized the horizontal oscillator with horizontal sync pulses. Vertical sync pulses are sent to vertical oscillator for synchronization.
Horizontal driver :- horizontal oscillator signal is amplified in driver stage. A driver transformer is used. The signal from secondary of driver transformer is given to base of horizontal output transistor. The collector supply to the output transistor is received from primary winding of EHT transformer. horizontal deflection Coils are connected to output of horizontal output section.
Horizontal output section:- It uses a power transistor (BU205, BU208), A EHT transformer and horizontal deflection coil placed in yoke which is mounted on picture tube neck. EHT transformer has few more winding which are used to generate 50 volt supply for vertical stage. 6.3 volt winding for picture tube(CRT) filament. Different EHT have some difference in auxiliary supply voltages.
Vertical stage:- This stage has in built vertical oscillator and vertical amplifier in a single IC. Vertical oscillator generate 50 hz saw tooth wave signal. After amplification this voltage is given to vertical deflection coil placed in yoke. The vertical oscillator uses vertical sync pulses received from sync separator to get synchronised with composite video signal. Vertical stage has two presets to adjust vertical hold of picture and vertical linearity of picture respectively.
Some common faults.
No light no sound :- problem of power supply.
Horizontal line:- problem in vertical stage.
No picture no sound but raster (light) is present :- fault is in VIF stage or in tuner stage.
Picture coming sound is not coming:- problem is in sound IF stage or audio amplifier stage.
Sound is OK but only plain light on screen :- problem in video amplifier stage.
Sound OK but no light : problem may be in horizontal oscillator or EHT section.
It is a very brief discription of black and white TV. Interested reader need to go for more details. Any question are welcome in comment. Thanks for reading.
three-phase-welding-rectifier circuit diagram with working principle
main-sections-of-lcd-tv/ LCD TV block diagram
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