Download Pattern Generator - Engineering Electronics

ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
AIM: Observation of various test patterns by using a TV pattern generater.
APPARATUS REQUIRED : T.V. kit, Pattern Generator ,connecting cord
THEORY:
Pattern Generator
The unique features of this instrument is that it has 12 patterns . Seven in color and five
in black and white . The 3 primary colors Red, Blue and Green and added to check the
purity of the colors. Guns can be aligned and repaired of the color TV sets with the help
of these 3 patterns.
RED
GREEN
BLUE
Contrast of the colors can be seen in Horizontal and Vertical position in different modes
of patterns provided in the color position, pattern one, color pattern two, color pattern
three and color pattern four give different sequence on the screen. Chess pattern can be
seen to check the contrast in Black & White.
RASTER
(CHESS PATTERN)
(SIDE CHESS PATTERN)
(CROSS BAR PATTERN)
Side chess pattern is provided to adjust the yoke position, Crossbar pattern is provided to
check the Linearity of the TV sets. Besides that video signals and sound signals (1KHz)
provide extra feature to this unique instrument. Audio sound lead is provided along with
the P.G. and can be easily connected in the socket provided at the back. This lead can be
connected with Tape Recorder to have direct sound on the T.V. set This will enable the
T.V. Engineers to see the clarity of the sound . Channel 2,3 and 4 can be had on band 1
and Channels 5 to 12 can be had on Band 3 with the help of push pull switch provided on
the front panel.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
PROCEDURE:


Switch On the Power ON/OFF switch .
Connect the Generator output to the T.V. Receiver and the following operations
are to be carried out.
OBSERVATIONS:
1. Press horizontal bar switch/or rotate switch for horizontal bar
(a) Observe the Horizontal Bar pattern on the T.V. screen, should the Bars move in the
Vertical direction. It is possible to hold them with the Vertical Hold Control. This
check is for frame time base frequency.
(b) Check that the White Bars are of the same height. ( i.e. check of frame time base
linearity).
(c) Check that the White Bars are of the uniform Brightness over the whole width (i.e.
check of low Frequency reproduction).
2.
Press vertical bar switch/or rotate switch for horizontal bar
(a) Observe the vertical bar pattern on the T.V. screen should the bars move in the
horizontal direction, it should be possible to hold them by means of “Horizontal”
stability control of the T.V. receiver (i.e. check the line time base frequency).
(b) Check that white bars are of equal width (i.e. check of line time base linearity ).
(c) Check that the black and White contrast is sharp enough (check of high frequency
reproduction).
3.
Press cross bar switch/or rotate switch for horizontal bar
(a) The white blocks serve for a general check i.e. rapid linearity check and check of
unit function response.
(b) Observe that white blocks are of the same size check of horizontal and vertical
linearity.
4.
AGC
This can be checked by switching from one pattern to another while observing for
any streaks in the pattern. Should the AGC be correctly adjusted no streaks would be
seen.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
5. FOCUS ADJUSTMENT
Use of dot pattern
Normally dots are slightly oval in horizontal direction if blurred or not clear,
Adjustment is required in contrast, brightness or focus circuits.
When the dots are tall at the right hand side or dim, adjust fine-tuning in case the
condition does not improve, adjust pictures amplifier circuit.
Different types of color patterns are available while rotating the switch at color
position different types of colors are available at different position, primary colors
Red, Blue and Green are the main features of P.G. Model 1000 and P.G. Model 14.
Specifications:
System
: PAL
Standard : CCIR Standard
Signal
: Patterns available
* Chess Pattern * Side Chess
* Vertical Bars
* Horizontal Bar
* Cross Bars
* Dots
* Raster White
Colour Signal
Frequency : 5.5 MHz with respect to video carrier frequency modulated by 1
KHz internally generated 50 KHz sweep.
Color Signal
:
4.4 33618 MHz Crystal controlled on all channel.
Picture Carrier
Frequency Band –I :
2,3,4
Band – III
Channel 5 to 12 channels
UHF Channel
:
:
36
Stability
:
Fairly good
Output
:
Fixed
Modulation
:
AM Negative
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
Sync Pulses
Line Frequency
:
15625 Hz (Fixed)
Frame Frequency
:
50Hz (Fixed )
Interlacing
:
Random
Stability
:
+1%
Output Impedance
:
300 Ohms balanced
Output Voltage
:
Approx. 10 mV
Sound
:
Frequency Modulation 1 KHz Approx.
Accessories
:
Leather case 300 Ohm RF. Lead
Power Supply Requirements :
230V 50Hz Single Phase
A
(CROSS BAR PATTERN) (DOT PATTERN)
RASTER
WHITE
RASTER
(CHESS PATTERN)
RED
(SIDE CHESS PATTERN)
GREEN
BLUE
BLUE
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
R
G
B
(COLOUR CHESS)
RESULT :
All the Patterns are study successfully by using pattern Generator.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
AIM: Operation of Monochrome T.V. Kit.
a) Study of Monochrome T.V kit
b) Study of TV Power supply
c) Study of Video Amplifier and EHT voltage Generator
APPRATUS REQUIRED : T.V. kit.
THEORY:
a) STUDY OF MONOCHROME T.V KIT
A Television receiver commonly called TV or Television set receives the
telecast signals and reproduces the televised scene and sound. The following
functions are performed by various stages of a television receiver.
1. To intercept the telecast signals, to select the signals of the desired channel and
to amplify these.
2. To separate the video (vision or picture) signals from the combined signals, to
amplify these and to reproduce these in to form of picture on the picture-tube
screen. This is done with the help of horizontal and vertical sweeps.
3. To separate the FM sound signals, to amplify to detect and to reproduce the
sound.
4. To separate the synchronizing signals (in brief sync signal ) from the
composite video-signals.
5. To produce horizontal (line ) and vertical (frame ) sweep signals,
synchronized with the help of sync signals and to give these to the respective
deflection coils producing the two sweeps.
6. To provide power at suitable D.C. voltages for operating various stages,
providing supply to various electrodes of the picture tube and for heating its
cathode.
The working of the various stages/sections of a solid-stage TV receiver has been
briefly described here with the help of the block schematic diagram in which various
stages have been depicted in the form of boxes.
While the number of ICs used in different models of TV receivers may differ, this
block schematic which is based on four ICs , represents a fairly balanced circuit
optimising the use of ICs.
Aerial :
The aerial picks up the telecast signals and gives these to the input of the tuner through
the feeder wire and an impedance matching transformer know as “ balun”.
Tuner: The signals picked up by the aerial are given to the tuner which consists of two
stages of RF amplifier and frequency changer (converter). The RF amplifier partly
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
selects the signals of the desired channel and amplifies these. The amplified signals are
given to the frequency changer.
The frequency changer (converter) performs two functions. Firstly it produces
oscillations at a frequency which is higher than the frequency of the incoming signals by
the intermediate frequency (IF) ,secondly it mixes the incoming signals and the
oscillations. This mixing results in the production of intermediate frequency (IF) signals.
Since there are two independent signals video and audio, two frequencies are produced.
The usual intermediate frequencies in the system used in our country are 38.9 MHz for
picture and 33.4 MHz for the sound respectively.
A single channel or multichannel tuner may be used depending on whether a receiver is
meant for single channel or multichannel reception. Bipolar tuners having turret tuning
or incremental tuning are common in multichannel TV receivers. Electronic tuners are
also gaining popularity.
Video If Section
The picture (vision ) and sound IF signals obtained from the tuner are given to the
video IF section. Two or three wave-traps are provided at the input of this section to
suppress the signals from the adjacent channels and also to reduce the amplitude of the
sound IF signals (to eliminate interference from these signals with picture signals).
The main functions performed by this section are amplification of the signals, detection
of the picture (video) IF signals to obtain the video signals, pre-amplification of video
signals mixing of picture and sound IF signals, resulting in the production of intercarrier
sound IF signal (5.5 MHz) keyed AGC for the IF amplifier and producing keyed and
delayed AGC voltage for the RF amplifier in the tuner.
As the band width of the picture signals is rather large, this section is designed to
provide adequate band width. Staggered tuned circuits (circuits tuned to different
frequencies ) are used for interstage coupling to obtain the desired band width. An IC
such as CA 3068 is normally used in this section.
Video Output:
The video output stage amplifiers the video signals obtained from the video (picture) IF
section and given these signals to the cathode of picture tube. As the bandwidth of the
video signals is rather large (from D.C. to abut 5.0 MHz) the video output section has to
be designed to provide sufficient gain over the entire band.
Three transistors are normally used in the video output section one as the driver the
second as output and the third for the horizontal and vertical retrace lines on the picture
tube.
picture tube :
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
The picture tube is a specially designed cathode ray tube which displays the video
signals in the form of picture on its screen with the help of horizontal (line) and vertical
(frame) sweeps.
Electromagnetic deflection is used in the television picture tubes. A set of two windings
one for producing the horizontal sweep and the other for vertical sweep, is placed on the
neck of picture tube. These are known as deflection coils or yoke. The sweep signals are
given to the respective windings of this yoke.
An IC CA 3065 (or similar) is commonly used in this section. The functions given
above, this IC also includes an electronic attenuator for volume control and a zener
diode regulated power supply for supplying its various stages.
Sound Output :
The sound (audio) signals obtained from the sound IF section are not of sufficient
amplitude to drive the loudspeaker. The output section amplifies the sound signals and
gives sufficient output power.
Two stages a driver and output are used in this section. The driver transistor (BC 148 or
similar) amplifies the sound signals obtained from the sound IF subsystem the output
stage, which normally is based on two transistors (matched pair of versa tile transistors
2N 5296 and 2N 6110 or similar types) in a complementary , symmetry single- ended
push pull circuit, further amplifies the sound signals and gives them to the loudspeaker.
Positive and negative flyback pulses are also obtained from this stage for keyed AGC,
line frequency control and suppressing the retrace lines on the picture tube. The line
output section utilises two transistor – one as driver and the other as output. A high
voltage power transistors such as BU 205/508A is used in the output stage.
Vertical Sweep-Section:
The vertical (frame) sweep-section produces vertical sweep signals and provides sawtoothed frame-sweep current to the frame (vertical) sweep coil. This section consists of a
controlled oscillator the frequency and phase of which are kept in synchronization by the
sync signals. This is followed by an amplifier cum output stage which amplifiers these
oscillations and drives quiescent current through the frame deflection coil.
An IC like IC 2130 is commonly used in this sweep current to the frame (vertical)
sweep coil. This section consists of a controlled oscillator the frequency and phase of
which are kept in synchronization by the sync signals. This is followed by an amplifier
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
cum output stage which amplifiers these oscillations and drives sufficient current
through the frame defection coil.
An IC like IC 2130 is commonly used in this section. In some earlier models
transistorized circuits have also been used in the sections.
b) STUDY OF TV POWER SUPPLY
Power Supply:
In solid state television receiver power is required at different D.C. voltage for operating
various stages. These are obtained from the main power supply and the auxiliary power
supply.
Main Power Supply :
The main power supply provides D.C. voltages of about 110 to 130 volts. This is
obtained by rectifying the mains voltage and smoothening it . This power from the main
supply is usually given to the video amplifier line output section and the grid of the
picture tube. A 12 volt supply is also obtained from it by dropping and stabilizing this
voltage, for feeding the line oscillator sub-section.
Auxiliary Power Supply :
The auxiliary power supply is a part of the line output stage. DC voltage ranging from
12 to14 volts are provided by the auxiliary power supply. These are used for supplying
to various sections operating at low voltage.
In some television receivers an IC like CA 810 may be used in sound section in place of
the transistors.
ICs are now available which are capable of performing the complete functions of sound
IF and sound output sections. CA 1190 (BEL) is an example of these ICs.
The auxiliary supply gives supply at three D.C. voltages –12 volts, 24 volts and 40 volts
A voltage of about 6.3 volts from the line output transformer is given to the heater of the
picture tube (pins 1 and 8).
line oscillator sub – section
The main function of the line oscillator is to produce oscillations at the line sweep
(15625 Hz). The frequency and phase of these oscillations is controlled by the sync
signals. A preamplifier for amplifying the oscillations and sync separator are also
included in this section.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
An IC like CA 920 (BEL) is commonly used in this sub-section. This IC combines the
following function sync- separator, noise-gating for reducing the effect noise pulses on
synchronizing, line oscillator, phase detector for comparing the phase of the line
oscillator with reference to sync signals (for correcting the oscillator phase and
frequency) and preamplifier.
line output :
The line output section is one of the most important section in a television receiver. It
provides saw-toothed line sweep current to the line (horizontal) deflection coil. It also
performs the following functions.
1. Producing a high voltage D.C. known as EHT (around 17,000 volts in black and
white television receivers ). This is given to the final anode of the picture-tube.
2. Producing a high voltage D.C. of about 1000 volts giving to the accelerating and
focusing anodes of the picture tube.
3. Providing low voltage A.C. for heating the filament of the picture tube.
4. Providing low voltage D.C. at suitable voltages for feeding some of the ICs and
transistors.
c) STUDY OF VIDEO AMPLIFIER AND EHT VOLTAGE GENERATOR
Generation Of EHT
As explained under generation of sweep, the collector current of the output transistor
builds up a magnetic field around the deflection coil during trace. When the deflection
current reaches its peak value the voltage at the base of this transistor suddenly falls to
zero and cuts- off this transistor. The magnetic field around the deflection coil will
therefore collapse. As the rate of collapse of the magnetic field is very fast a high voltage
is induced in the primary winding of the line output transformer. This voltage is further
stepped up by the secondary winding which consists of a large number of turns.
The voltage obtained at the secondary winding is rectified by a diode and is smoothed by
the capacity formed between the inner and outer coating in the picture tube. This
provides a D.C. voltage of about 17000 volts.
A high voltage is also induced during retrace on the primary winding of the line output
transformer.
Flyback Pulses
During the retrace, pulses are also induced in the windings of the line output
transformer. The pulses so obtained are given to the line oscillator IC CA 920 to serve as
reference of oscillator for correction of its phase. These pulses are also given to the video
amplifier for suppressing the horizontal retrace lines.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
AIM: Switching Mode Power Supply
APPARATUS REQUIRED : T.V. kit
THEORY:
Different types of power supply are used in electronics equipments. Earlier
high voltage capacity power supply was made directly from 220/230 A.C.
supply. For generating low voltage supply we use resistance in high voltage
supply according to necessity. Capacitor and coil are used for filtering A.C.
pulse and ripples. After few years, transformers are used for making lower
supplies. In both types of power supplies output voltage changes according to
input A.C. volts, it means when input A.C. voltage increases output D.C.
voltage also increases & if input A.C. voltage output DC volts also decreases.
This type of power supply is called unregulated power supply. But when we
use ICs for making electronic equipments, it is necessary to use regulated
supply. Use of transistorized series regulator does not solve the problem
because of working efficiency being up to 25% to 40%. SCRs also losses
energy ,because of which we can’t use SCR power supply for high rating. So
there is a necessity to use power supply having high working efficiency about
80% with low cost.
SMPS power supply
The use of Switching Mode power supply started from 1980. In SMPS
switching transistors are used for controlling output supply which will ONOFF at particular frequency.
Principal Of Switch Mode Power Supply:
The output value of any power supply section depends on given input supply.
If we stabilized input A.C. voltage by any method then output supply will also
stable, SMPS works on the same principle. At first main input A.C. is
converted in to high D.C. voltage and by using filter capacitor we get smooth
D.C. which is given to switching transistor.
By control circuit we can ON-OFF transistor very rapidly. This control circuit
generates high frequency square wave pulse (15KHz to 20KHz ) which is
given at base of transistor .ON-OFF of transistor depends on this pulse these
pulses are given at primary of small size transformer and appeared voltages at
secondary are rectified and filtered figure 1 shows block diagram of simple
SMPS.
In switch mode power supply we get low voltage D.C. supply whose value
varies from 12 volt to 20 volt, along with main D.C. supply of +110 volt. For
regulating this output, one part of output is given to sense amplifier. This
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
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TELEVISION ENGINEERING
amplifier compares output with reference voltage. If there is a difference in
both voltages then error voltage will develop, which is given to control circuit
used for controlling ON time (duty cycle ) of switching transistor according to
error voltage and develop output regulated voltage if there is increment in
output voltage then developed error voltage reduces ON time of switching
transistor, so in both stages we get regulated output supply. SMPS also has
some characteristic, for example starting of switching process at low current,
protecting circuit from high current and voltage and separate output supply
with main supply. Most of SMPS use one or two transistors. These days we
get necessary frequency for switching and regulating output voltage from I.C.
we clarify you that when ON-OFF process of switching transistor is done at a
fixed transmitting frequency then we get fixed supply at primary of
transformer, because of that value of secondary voltage is also fixed after
rectifying and filtering we get D.C. voltage at output.
For regulation output D.C. voltage switching process of switching transistor is
controlled by one control circuit. We have to keep in mind that supply at
secondary of SM transformer is output supply, which is separated from D.C.
supply made by input A.C. main characteristic SMPS is that there is separate
input and output supplies, which protect main circuit after starting of
switching transistor.
PROCEDURE :
1. Connect 34 pin connector cable from Dynamic Demonstrator to left side
of the CRT cabinet.
2. Connect the Antenna cable to the Dynamic Demonstrator.
3. While switching on the Demonstrator (before plugging into AC-mains )
ensure that SMPS switch is in OFF condition.
4. Do not adjust or align vision if Board preset or coil.
5. Ensure that EHT cable is connected to picture-tube before system is
switched ON.
6.
Do not keep” horizontal control “ to maximum position as it may
Damage horizontal IC, or output transits BU205/508A.
7.
Do not interchange horizontal & vertical yoke connections.
8.
After checking the above points switch ON the trainer.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
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TELEVISION ENGINEERING
AFTER SWITCHIG ON THE TRAINER THE FOLLOWING ALIGNMENTS
HAVE TO BE MADE
1. To get clear picture select the appropriate channel in the tuner.
2. Align “vertical hold “ and horizontal hold” controls for correct picture so that
you will not get horizontal and vertical rolling.
3. Adjust the volume control to a suitable audible level.
FAULT INDUCING SWITCHES
OBSERVED PROBLEM/DEFECT
F1
F2
Switch OFF dot ON the screen, sound ok
Audio ok but no picture, only snow raster ON
the screen
Sync signal loss
Horizontal line
No Sound ,picture ok
No picture, Sound ok, Darkness appears on the
screen
F3
F4
F5
F6
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
AIM: Operation of Color T.V. Demonstrator.
a)
b)
c)
d)
Observing the effect of various fault induced by various fault inducing switches.
Measurement of signal in RF Tuner section
Measurement of signal in Video IF and AGC section.
Observation of waveforms Generated by Horizontal Sync Oscillator.
APPARATUS REQUIRED : T.V. kit, CRO, Multimeter ,connecting chords
THEORY:
Lab Color TV Dynamic Demonstrator is a comprehensive trainer. In this
Demonstrator all importance has been given to practical study of various parameters
involved in a color television.
1.
2.
The Block Diagram of the Lab Color television Demonstrator (using ET &
T kit ) is printed on the front panel of the Demonstrator.
The picture tube is housed in the cabinet and connected to the mother
board by means of polarized connector.
Fault inducing switches (F1to F2) are provided at the right hand side of
the top panel in the Demonstrator to study the relationship between cause
and the effect.
The circuit of power supply, tuner, Vision IF Sound IF, vertical sweep
section, Horizontal sweep section, Horizontal output & EHT generator,
Chroma section are assembled in the mother board and explained by
means of block Diagram in the trainer.
Various test point TP1 to TP24 are provided to check the voltages in
different sections using a multimeter and also to observe to the waveforms
on an oscilloscope.
Antenna connector (impedance matching Balun transformer) is provided
in our Demonstrator.
Channel selector is mounted in the picture tube cabinet control elements
like volume control Brightness control, contrast & color adjust controls
are mounted in the picture tube cabinet.
34 pin FRC connector 9pin D connector is provided to connect picture
tube and mother board.
3.
4.
5.
6.
7.
8.
PROCEDURE:
1. Connect Antenna cable to the Demonstrator.
2. Connect 34 pin connector and 9 pin “ D “ connector from the mother
board to the picture tube.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
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3. Connector 24 KV (HT probe Red) from the mother board to the picture
tube properly you will have to be extremely careful when you connect this
cable.
4. Focus cable from the Demonstrator (white cable) should be soldered at
the base of the picture.
5. Check whether all the connections are connected properly.
6. Plug – in power cord to 230V50Hz main.
7. switch ON the trainer.
8. Now ,you can see the picture as relayed by the transmitter depending upon
the channel you have selected.
9. Alternatively a patter generator can be connected instead of antenna cable
and Different patterns can be observed on the TV monitor.
10. As soon as the picture comes adjust the appropriate brightness, contrast &
Color controls for your viewing comfort.
Use the fault inducing switches from F1 to F10 and see the following effects:
a. F1-To observe retrace lines. If you put F1 switch to UP position you
will observe no picture and sound in your Demonstrator you will
observe retrace line in your monitor.
b. F1- you will notice phase shift in the picture.
c. F3- cutoff the GREEN color in RGB spectrum.
d. F4– To cutoff the BLUE color in RGB spectrum.
e. F5– To cutoff the RED color in RGB spectrum.
f. F6- To cutoff the vertical sweep section,you will observe horizontal
line on your monitor.
g. F7- To introduce the vertical linear variation in the picture.
You will observe that the picture is vertically non-linear, sound
normal.
H F8- To cutoff brightness control.
h. F9-To cutoff Audio signal
i. F10 To cutoff vision IF section To cutoff 115v from vision IF
CAUTION DO NOT KEEP THE FAULT INDUCING SWITCHES F1 – F10
IN THE ON POSITION FOR NOT MORE THAN 45 SECONDS.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
Various test points are provided to test and measure input and output signals
j.
SMPS section
TP1 - +150DC
TP2 - + 100DC
TP3 - + 15VDC
k. Audio section
TP4 - +3.6V DC
TP5 - +4V DC
TP6 - + Audio output should be observed in oscilloscope
l. Vertical sweep section
TP8 _
TP9 - SEE PAGE NO. 4
m. Vision IF section
TP16 - +6V
TP17 - +1.25V
TP18 - +12 .10V
n. Horizontal Driver output
f.
TP19
TP20
TP21
TP26
TP22
TP23
TP24
-
1.2V
+90V
+ 85V
+86V
+14.8V
+1.2V
+85V(Approx) Driver
TESTING POINTS OF OUTPUT PIN DETAILS
TP4
TP5
TP6
TP7
TP8
TP9
-
TP10
TP11
-
TP12
TP16
TP17
TP18
-
OUTPUT IC 1190 PIN NO:12
OUPUT OF 5.5 MHz COIL
OUTPUT OF SPEAKER
OUTPUT OF IC 2653 PIN NO: 2
OUTPUT OF IC 2653 PIN NO :1
OUTPUT OF IC 2653 PIN NO: 2
AFTER DIODE IN 4148
OUTPUT OF IC 2653 PIN NO: 6
OUTPUT OF IC 2653 PIN NO:2
(OUTPUT OF IC 2653 PIN NO: 2)
OUTPUT OF IC 2653 PIN NO: 4
OUTPUT OF IC 1940 PIN NO:5
OUTPUT OF IC 1940 PIN NO: 3
OUTPUT OF IC 1940 PIN NO:11
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
ELECTRONICS & TELECOMMUNICATION DEPARTMENT
TELEVISION ENGINEERING
TP19 - OUTPUT OF HORIZONTAL DRIVER
TRANSISTOR BD 115 BASE
TP20 - OUTPUT OF HORIZONTAL OUTPUT
TRANSISTOR BU208D COLLECTOR
TP21
-
OUTPUT OF HORIZONTAL DRIVER
BD 115 COLLECTOR
BLOCK DIAGRAM OF ET&T COLOR TELEVISION KIT
The block diagram of color Television kit given in figure. The function of each block
are explained below.
ANTENNA
The main function of antenna is to accept the electromagnetic wave coming from
television transmitter. The antenna receives the electromagnetic waves and converts into
RF signals which is given to the television receiver.
For better reception of RF signal YAGI antenna is most commonly used in all
television receivers in VHF/UHF range for its simple construction and low air resistance.
BALUN
It is used for matching the impedance of balanced 300 ohm line to unbalanced 75 ohm
tuner input impedance. RF signal from antenna is given to the RF tuner through the balun
transformer.
b)
MEASUREMENT OF SIGNAL IN RF TUNER SECTION :
RF Tuner
It is used for better picture and sound reception the main functions of the tuner are
1. It selects station and rejects others
2. it matches antenna with Television receiver because of this ghost image can be
removed
3. It converts RF signal into intermediate frequency by heterodyning it with local
oscillator frequency
4. It isolates the local oscillator signals from the antenna for preventing radiation of it
through the antenna.
5. it rejects the image frequency which causes the ghost image along with picture
The RF tuner selects RF signals of desired (selected) channel, amplifies them and
converts them into IF signals the tuner consists of an RF amplifier an oscillator and a
mixer stage.
ORIENTAL INSTITUTE OF SCIENCE & TECHNOLOGY
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Local oscillator generates a constant frequency for desired channel RF amplifier the
RF signal achieved from antenna and mixer stage converts them into IF signal by
heterodyning RF signal with local oscillator frequency
The IF carrier frequency present in IF signals for picture and sound are 38.9MHz
and 33.4MHz respectively, thus IF signal achieved from tuner is fed to the IF
amplifier.
C) MEASUREMENT OF SIGNAL IN VIDEO IF AND AGC SECTION.
IF PRE – AMPLIFIER
It amplifies the IF signal. This stage of amplification is necessary because by the
use of saw filter the gain of receiver becomes less.
SAW – FILTER
On this kit saw filter is used in place of wave trap circuit. It passes only required
frequencies and grounds unwanted adjacent channel frequencies.
VIDEO IF STAGE
In ET & T kit IC1 (TDA3541) is used in video If stage. This stage contains the
function of video IF amplifier, video detector video pre-amplifier AFC and AGC
circuits etc.
VIDEO IF AMPLIFIER : It amplifies the IF signal to provide sufficient gain AGC
voltage is applied to all the separate IF amplifiers, except the last IF amplifier from
video IF amplifier the signal is applied to the video detector two or three stages are
used in this amplifier stage.
VIDEO DETECTOR : Signal obtained from video IF amplifier is injected to the
video detector. In video detector the signal is demodulated giving back the y-signal
(luminance) and the color side-band along with various synchronizing pulses and the
color burst signal AFC signal is also given to tuner section for automatic frequency
control.
Another main function of video detector section is to mix the picture IF
(38.9MHz) and sound IF (38.9MHz) frequency to produce a new sound IF at
5.5MHz.from here new sound section. L-C filter or 5.5MHz tank circuit is also used
with video detector to remove the 5.5MHz inter-carrier sound signal from video
signal.
The video signal obtained from video detector is then applied to the video
amplifier. This amplifier is coupled to video pre-amplifier as well as AGC sections.
SOUND SECTION
SOUND IF AMPLIFIER : THE 5.5MHz inter carrier signal from video detector
stage is fed to the sound IF amplifier for proper amplification In this kit sound signal
is preceded by a crystal (ceramic filter) tuned at 5.5MHz.
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F.M. DETECTOR :
5.5 MHz sound IF signal is amplified by one or two sound IF amplifier stages and
then applied to detector stages and then applied to detector stage. In this stage
original sound signal is detected from the carrier.
AUDEO AMPLIFIER : In this stage voltage amplification and power amplification is
given to the audio signal finally fed to the speaker.
VIDEO PRE-AMPLIFIER
From the output of video amplifier in the video IF stage the video signal is fed to the
video pre-amplifier .the signal consists of
1 The luminance or Y-signal
2 The color sub-carrier containing red and blue color difference signals,
3 The horizontal & vertical sync pulses,
4 The color burst signal
The video pre-amplifier section amplifies the signal strength from 2V to 6V so that it is
able to drive video output stage. Here the division of the luminance & chrominance
separation takes place.
From video pre-amplifier, video signal is coupled to chroma band pass amplifiers
through chroma filter circuit, sync separator and delay line circuit.
DELAY LINE
From video pre-amplifier, Y-signal (luminance signal) passes through a delay line to
amplifier stage. The delay line delays the y-signal (luminance signal) by approximately
0.8 microsecond. The delay line is a special coil with very high value of inductance and
distributed capacitances so that the delay speed of the signal through the delay line is
greatly reduced.
It this delay line is not introduced, y-signal (luminance signal) will reach to
picture tube earlier than chrominance signal.
The main reasons for required delay in Y-signal (luminance signal) are as under,
1 Chrominance signal has to pass through relatively complex circuit of the decoder and
by this reason, it is fractionally delayed as compared to y-signal (luminance signal).
2. the band with of Y-signal (luminance signal) is more than that of chrominance signal
the narrower band with signal takes longer time to travel a particular distance.
The Luminance Amplifier
After the delay line ,the Y-signal (luminance signal) is fed to main Y (luminance)
amplifier. The circuit used is also called emitter follower which acts as buffer amplifier to
prevent any mutual interference between contrast control and black level clamp circuits.
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The output signal voltage from Y (luminance) amplifier is fed to the matrix where it
mixes with color difference signals to produce original red, green and blue colors.
The horizontal and vertical blanking pulses derived from horizontal output and vertical
output stages are also fed to Y (luminance) amplifier stage. These pulses ensure that the
Y-signal (luminance signal) fed to the matrix is held at black level during retrace periods.
The average value of luminance signal fed to the matrix unit determines the mean
brightness of the picture appearing on the screen the contrast control is used for adjusting
the amplitude of the Y-signal (luminance signal) from the amplifier.
Chroma Section
IC TDA360/3561 is used in this section.
Chroma Band Pass Amplifier
From the output of video pre-amplifier the composite color video signal is coupled to
chroma band pass amplifier it consists of chroma filter 4.43MHz and two stage of chroma
amplifiers.
The chroma filter circuit separates modulated chrom sub-carrier signal and the color
burst from incoming composite video signals.
These separated chroma signals are amplified by the first chroma amplifier which is gain
controlled by the voltage developed by the automatic chroma or color control (ACC)
amplifier.
The output from the first chroma amplifier goes to both the second chroma amplifier and
burst pre-amplifier. The second chroma amplifier incorporates color saturation control
circuit. The output of color killer also feeds into it because of this the 2nd chroma
amplifier is cut off during black and white reception.
Color Burst Circuit
The color burst circuit consist of the burst pre-amplifier pulse and shaper and the gated
burst amplifier.
After Demodulation detected U(i. E. B-Y) and V(i.e. R-Y) color difference signals are
fed to the matrix from which separate red green and blue color signals are available.
Luminance (Y) signal is also fed to the matrix.
R-G-B Video Output
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The color video signals red green and blue are then fed to respective cathodes of picture
tube after one stage of amplification video output circuits for each color signal are
identical
c) OBSERVATION OF WAVEFORMS GENERATED BY HORIZONTAL SYNC
OSCILLATOR.
HORIZONTAL SECTION
IC3 (tda 1940F) is used in this section SYNC SEPARATOR FROM THE EMITTER of
video pre -amplifier, composite color video signal is fed the sync separator made inside
the IC TDA1940F. here horizontal and vertical sync signals are separated by the use of
suitable integrated and differentiator circuit this stage also amplifies circuit. This stage
also amplifies both horizontal and vertical sync signals.
AUTOMATIC FREQUENCY CONTROL OR AFC CIRCUIT:
This stage is included in IC TDA1940F this section compares the horizontal flyback
pulse and incoming horizontal sync signal the difference between these two appears as
control voltage for controlling horizontal oscillator frequency.
HORIZONTAL OSCILLATOR:
This oscillator generates 15625Hz saw-tooth horizontal (line ) frequency for horizontal
deflection of electron beam inside the picture tube its frequency is controlled by the
control voltage obtained from AFC circuit.
HORIZONTAL DRIVER :
The signal obtained from horizontal oscillator is very weak and so it is necessary to give
voltage and power amplification to this signal in this stage voltage amplification is
provided and sent to the horizontal output stage through the horizontal driver transformer
transistor T9 (BDS 115) is used in this section as horizontal driver transistor.
HORIZONTAL DRIVER TRANSFORMER : it is used to match the high impedance
of driver stage with the low impedance of out put stage.
HORIZONTAL OUTPUT STAGE : this stage consists of a transistor and EHT
transformer power amplification is provided to the horizontal scanning frequency
(15625Hz) and then this frequency is fed to horizontal deflection coil and EHT
(horizontal output transformer)
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Some auxiliary power supplies are obtained from this stage such as 25v, 12.6v,13v 150v
and supply for heater high voltage (about 20KV to 25KV) is also produced for final
anode of picture tube horizontal fly back pulse is achieved from EHT (horizontal output
transformer).
VERTICAL STAGE
In this kit IC TDA2653A is used in vertical section. This section consist of vertical
trigger cum vertical oscillator vertical driver and output amplifier.
VERTICAL OSCILLATOR : it is triggered by the frequency of vertical sync pulse
achieved by the integrator circuit thus it provides the 50Hz saw-tooth frequency
necessary for the vertical deflection of electron beam inside the picture tube.
VERTICAL DRIVER : It provides voltage amplification to the vertical signal, obtained
from the oscillator.
VERTICAL OUTPUT:
It provides the sufficient power amplification to the vertical scanning frequency (50Hz)
and then it is
Frequently Asked Question’s:
1.
2.
3.
4.
5.
6.
What do you understanding by interlaced scanning.
How interlaced scanning is reduces flicker and conserve bandwidth
Why is the picture signal AM and sound signal FM modulated
Define aspect ratio
Why is Electro magnetic preferred over Electrostatic deflection
Why front porch and back porch provide along with the horizontal sync.
Pulse.
7. what are the functions of brightness and contrast control.