April 19, 2017 | Author: Shrikant Jahagirdar | Category: N/A
Colour Television Trainer ST2651
Learning Material Ver 1.1
An ISO 9001:2008 company Scientech Technologies Pvt. Ltd. 94, Electronic Complex, Pardesipura, Indore - 452 010 India, + 91-731 4211100, :
[email protected] , : www.ScientechWorld.com
ST2651
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ST2651
Colour Television Trainer ST2651 Table of Contents 1. 2. 3. 4. 5. 6. 7. 8. 9.
Introduction Features Technical Specifications Safety Precautions Trainer Controls Block diagram Theory of Operation Getting Started Experiments
5 6 7 8 9 11 12 14
•
Experiment 1 Study of circuit description of RF Section (Tuner Section) Experiment 2 Study of RF Section through Test Points Experiment 3 Study of fault simulation and step-by-step fault finding Procedure of RF Section
15
•
Experiment 4 Study of detail circuit description of VIF section
22
•
Experiment 5 Study of VIF Section through Test Points
25
•
Experiment 6 Study of fault simulation and step-by-step fault finding Procedure of VIF Section
26
•
Experiment 7 Study of detail circuit description of Video & Chroma section
28
•
Experiment 8 Study of Video & Chroma section through Test Points
31
•
Experiment 9 Study of fault simulation and step-by-step fault finding procedure of Video & Chroma Section
33
•
Experiment 10 39 Study of detailed circuit description of Horizontal Oscillator Section and Horizontal Output Section
•
Experiment 11 Study of Horizontal Oscillator and Horizontal Output Section through Test Points
• •
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10.
Experiment 12 Study of fault simulation and step-by-step fault finding procedure of Horizontal Oscillator and Horizontal Output Section • Experiment 13 Study of detailed circuit description of Vertical Oscillator and Vertical Output Section • Experiment 14 Study of Vertical Oscillator and Vertical Output Section Through Test Points • Experiment 15 Study of fault simulation and step-by-step fault finding procedure of Vertical Oscillator and Vertical Output Section. • Experiment 16 Study of detailed circuit description of R-G-B Video Output Section • Experiment 17 Study of detailed circuit description of Sound Output Section • Experiment 18 Study of fault simulation and step-by-step fault finding procedure of Sound Output Section • Experiment 19 Study of detailed circuit description of AV Section • Experiment 20 Study of fault simulation and step by step fault finding procedure of AV Section • Experiment 21 To study the detailed circuit description of System Control Section • Experiment 22 Study of System Control Section through Test Points • Experiment 23 Study of fault simulation and step-by-step fault finding procedure of System Control Section • Experiment 24 Study of detailed circuit description of Power Supply (SMPS) Section General Details for Servicing
11.
Preset Layout Diagram
84
12.
Actual Shorting Shunt Position of Jumpers
85
13.
Glossary
86
14.
Warranty
94
15.
List of Accessories
94
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52 54 55
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61 64 67
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ST2651
Introduction Scientech Colour TV Trainer ST2651 is an ideal training equipment to instruct the operation of colour television receivers. It is demonstrator cum trainer specifically designed for the study of working of television. The controls are placed actually at the places as they are in the circuit schematic, thus trainee can look at any section, & can see components of the section and is able to study it thoroughly. The function controls are adjustment control fully adjustable to the trainee to verify their affect on the working of the television. One of the main features of this trainer is fault simulation to train on actual fault finding, by simulating faults in the instruments. The faults created in the instruments, no way affects nor damages the instrument. The instructor can introduce faults of his/her choice from the standard 48 faults and ask trainee student to probe into it and to find out the cause of the fault. This way trainee gets complete insight of training of faults in the electronic circuit. The complete circuit of colour TV receiver is printed on single printing PCB. Each section is colourfully separated. Test point details with typical voltages and waveforms are provided in the manual. The trainer has a special design of sliding main board with lock facility. It can be also used as a normal desktop colour TV receiver. In addition the trainer will be of immense value to practicing engineers and students engaged in study of TV receiver. The trainer has been designed to meet the requirements of electrical and electronics engineering student at the degree level. It will also meet the comprehensive practical study on TV engineering in polytechnics and technical institutes. The trainer has been designed that any engineering student with a basic knowledge of the various electronic building blocks and fundamentals of communication system will have no difficulty in understanding the trainer. We hope our attempt will help the user to understand the working of colour television receivers.
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ST2651
Features •
Most compact design
•
Sliding main board with lock facility
•
Manual and remote control operation
•
Fault creation and diagnosis
•
55 Test Points
•
Colourful separation of each section
•
No soldering/de-soldering is required to simulate fault
•
The trainer works as normal TV when the controls are normal
•
All the variables/adjustments via, Height, Linearity, White balance etc. are accessible on the screen itself with On Screen Display (OSD)
•
Explanation, observation, alignment and adjustment of internal and external controls are possible at a glance
•
The complete-circuit diagram is given in the manual with detail component list of each section and diagram of SMPS transformer, EHT, driver transformer, etc
•
A complete preset layout is given in the manual to locate easily any preset
•
Every preset has calibration indicating on dot
•
Track layout from solder side is also from component side for easy understanding of the circuit
•
Test point detail with typical voltages and wave forms are provided in the manual
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The whole circuit of remote Colour TV trainer is explained section wise in detail in the manual with alignment / fault finding techniques
•
The trainer is free from electrical shocks, variations and provided with enough safety precautions
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ST2651
Technical Specifications Standard
:
CCIR-B-P AL-G, 625 Lines
Channels
:
230Nos 2-4 VHF I (VL) 5-12 VHF III (VH) 12-100: Band IV & V else: S band & Hyper band
Picture Tube Size
:
36/ 51 cm Diagonal
RF input impedance
:
75Ω
Circuit Blocks
:
System Control Circuit, Video IF, Sound Section, Tuner Section, Horizontal Oscillator, Horizontal Output, Vertical Oscillator, Vertical Output, Video & Chroma Section, Power Supply, AV Sections.
ON Screen Display to set
:
Panel Control
:
Volume, Brightness, Contrast, Colour, Channel & Band Selection, Tuning. ‘On-Off’ switch, stand by Menu, Vol +/- Prg. +/
Remote Control Function
:
Volume, Brightness, Stand by, Colour, Contrast, Channel Selection, Audio Mute, AV Mode, Zoom, Swap, Scan, Child Lock.
PCB Size (mm)
:
475 × 375
No. of Faults
:
48 Nos.
No. of Test Points
:
55 Nos.
I. F. Frequency
:
Video-38.9 MHz Audio-33.4 MHz
Speaker Size (mm)
:
50 × 125
Accelerating Potential
:
24 KV Maximum
Operating voltage for EHT :
110V
Power Supply
:
230V, ±10%; 50 Hz
Power Consumption
:
75Watts (approximately)
Fuse
:
2A
Dimensions (mm)
:
W610× D530× H640
Weight
:
32 Kgs. (approximately)
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ST2651
Safety Precautions •
Voltages and waveforms of EHT, SMPS transformer and horizontal deflection coil of yoke, should be measured carefully.
•
One should wear insulating shoes while testing the trainer.
•
All the voltages should be measured with reference to main ground only, unless specified.
•
Do not touch the EHT transformer, EHT cable, Screen cable and picture tube earthing
•
Do not bring any metal part near to EHT
•
Yoke convergence assembly should not be disturbed
•
Do not touch 230V AC mains connector and degaussing coil connector
•
Do not touch AC fuse, and rectifier section in SMPS
•
Never connect SMPS ground with main ground.
•
Do not vary Focus preset and Screen preset
•
While observing the signal on CRO assure that the ground of CRO probe is correctly connected
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Do not disturb any coils
•
Do not vary horizontal hold preset towards high frequency side
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The trainer should not be kept in ‘On’ condition for long time when PCB is inside the enclosure box, to prevent it form heating
•
Always use 3 pin connector to mains with protective earthing
•
Do not remove acrylic sheet
•
All the measurement should be done with extreme care.
•
Do not operate in high humidity conditions, i.e. above 90% RH and 40°C. Refer service to authorized service personal only.
•
Keep the unit away from radiators and other heat sources.
•
Avoid using the trainer near strong magnetic field
•
While creating fault of H. line, operate with low brightness. This ensures long life of picture tube.
~
Warning To reduce the risk of fire or electrical shocks, do not expose this unit to rain or moisture
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ST2651
Trainer Controls Front Panel Controls Power ‘On’/ ‘Off’
: To turn the TV to standby mode.
S/BY
: To turn the TV ‘On’ (It works when power ‘On’)
Menu
: To display the menu on screen.
Vol q
: To decrease the volume (during on screen display mode it is also used to set the selected items)
Vol p
: To decrease the volume (during on screen display mode it is also used to set the selected items) : To cyclically select channels (during on screen display mode these switches are used to select items).
Prog p/q Audio-Video In Sensor Front Lock
: Sockets are provided to connect audio - video signal from other audio - video equipments) : It is a remote sensor which receives infrared signals from the remote control. : To open the enclosure so that you can pull the PCB outside the cabinet for testing purpose
Rear Panel Control: Aerial Jack (Antenna Socket)
: To connect the cables.
Mains Cord plug
: To connect the cable
26 pin IDC connector : To connect the cable 11 pin octal connector : To connect the cable 8 pin octal connector : To connect the cable Remote Controls: Power
: To turn the TV ‘On’ from stand by mode.
Mute
: To mute volume.
Number Buttons (0-9) :`To select the channels directly. −/−−
: To switch channel numbers among single digit double digit and triple digit.
CH/P
: To select the channels cyclically. Also used for selecting the items during on screen display mode.
Vol (+1- )
: To adjust the volume. During on-screen display mode these buttons are used to set the selected items.
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ST2651 Menu: I
: By pressing this switch, first the following this menu appears on the screen. a. Brightness b. Contrast c. Colour Above functions can be selected by PROG p/q and parameters can be varied by volume (+/-) Keys.
II
: By pressing this switch following menu appears on the screen a. Store
b. Search
d. Fine
c. Auto Tune
Above functions can be selected by PROG p/q keys and parameters can be changed by VOL (+/-) keys and options can be stored by selecting store function and pressing VOL (+) III
: By pressing this switch three times following menu appears on the screen. a. SKIP
IV
b. ‘Off’
c. ‘On’
SKIP function can be selected by PROG p/q and set by Vol (+) key. : By pressing this switch fourth time the following Menu appears on the screen a. Store
b. English
c. Hindi
Functions can be selected by prog. p/q keys and stored by selecting Store and pressing VOL (+) key, AV
: This mode is provided to connect Audio - Video Equipment with TV.
PP
: To restore the values of Brightness contrast, Colour, Volume stored in PP.
Scan
: On activating this feature the TV displays the programs in all the channels for a few seconds. : It enables one shot exchange of pre-tuned channels between two programs.
Swap Zoom (∧/ V)
: This facility allows the image on screen to expand and fill the screen.
Child Lock
: This feature allows you to lock a few channels by your remote control so as to prevent your children from watching them.
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ST2651 Block Diagram Colour TV Trainer ST2651
Figure 1
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ST2651 Theory of Operation The basic objective of colour TV trainer is to study all the signals or voltages in different sections of the circuit. The RF signal received by antenna is fed to the tuner section by antenna wire. Tuner section separates the IF signal from received RF signals. These IF signals are supplied to VIF and SIF section. This IF signals are here amplified by video IF amplifier and then detected by video detector. So in this section composite colour video signal is obtained. Sound signals are separated from this composite colour video signal by a SIF filter and then fed to sound IF amplifiers. Sound IF amplifiers amplify the sound signal which is then detected by FM detector. Audio amplifier amplifies the detected audio signal which are again amplified by audio output amplifier and fed to speaker. Composite colour video signals are supplied to video/ chroma section (IC CD7698). This video signal contains Horizontal and Vertical sync signals. Both the signals are separated by sync separator. Vertical signal is amplified by vertical amplifier and drive by vertical driver section, its output is fed to vertical output section where two output transistors are used. Amplified output is supplied to vertical yoke coil, at the other end if this coil vertical feedback is provided from vertical amplifier section. Horizontal synchronous signal is fed to Automatic Frequency Control section which is used to stabilize the output of Horizontal Oscillator to 15,625 Hz. From here, signals are fed to Horizontal Driver Section. In this section mainly a transistor and a horizontal driver transformer is used. Output of horizontal driver transformer is given to horizontal output amplifier transistor, where signal is amplified. This amplified output signal is supplied to horizontal deflection yoke coil. This yoke coil is used to spread electron beam is left/right direction horizontally. Composite colour video signal given to IC CD7698 separates luminance signal and chrominance signal from this composite colour video signal. Luminance signal is black & white signal. In black and white TV, only this signal is produced and used. Chrominance signal contains three colours which are red, green and blue. So from this section three type of signals are emerged which are as follows. •
G - Y Signal
•
R - Y signal
•
B - Y signal
These three coloured Y signals are fed to red output, green output and blue output transistors amplifiers. Amplified three coloured output signals are fed to green, red blue cathodes of picture tube. Luminance signal emerges from IC7698 and is amplified by luminance amplifier. Amplified luminance signal is supplied to the emitter of all the three colour transistors. Each output transistor gets colour difference signals at there base and luminance signal on their emitter which mixes them the amplified signal is transmitted as corresponding colour. For white balancing, three presets are provided, which are adjusted such that the
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ST2651 percentage of colour should be in following equation. Y = 0.59% Green + 0.30% Red + 0.11 % Blue When this equation is satisfied we can get better results on the screen. The power supply circuit provides the necessary operating voltages for the instrument input AC supply 230V is provided to bridge rectifier. Its output is 300V DC. This DC voltage is provided to SMPS transformer. This Transformer provides +22V, +110V, +33V DC supplies which are used in various circuit sections. EHT transformer supplies +22KV (EHT) accelerating potential to final anode of picture tube. EHT transformer also produces AFC fly back pulses. Focus and screen voltage are produced by EHT Transformer fed to the picture tube at G2 and G4 (grid). Heater filament is supplied by EHT transformer pin no. 9. The main controlling system for this trainer kit is, system control section. It is IC FONDA4ST. This system controls IC control all the remote control functions as well as front panel control like volume, brightness, contrast, colour menu etc. This IC system is also related with memory section, which can store the channels in its memory and similar functions can also be stored in it.
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ST2651 Getting Started •
Connect the television monitor Supply to the base unit
•
Connect the antenna cable to the base unit
•
Connect one end of 26 pin flat cable to base unit & the other to monitor
•
Connect one end of 8 pin octal cable to base unit & the other to monitor
•
Connect one end of 11 pin octal cable to base unit & the other to monitor
•
Connect the AC mains cord to the monitor
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ST2651 Experiment 1 Objective: Study of circuit description of RF–Section (Tuner section) RF–Section (Tuner section): The RF-Section is mainly consisting of RF Tuner. This tuner has RF amplifier, a mixer and a local oscillator. The antenna receives the radio frequency (RF) waves from the atmosphere and converts them into corresponding signal variations. These RF variations are fed to RF tuner. The input impedance of RF Tuner is 75 ohms. The antenna system and co-axial cable should be properly matched. If a co-axial cable of 75 ohms impedance is employed, there is no need of any extra matching device between cable and antenna socket at the receiver. But in case if a feeder wire of 300 ohms is employed then an impedance matching transformer (300-75ohms) is added between feeder and antenna socket at the receiver. There is also a need of impedance matching between output terminals of antenna and co-axial cable or feeder wire. The RF tuner selects the signal of the desired channel, amplifies it and converts in to Intermediate frequencies (IF). The video IF is at 38.9 MHz and sound IF is at 33.4 MHz. Tuner section has +12V approximately supply voltage at TP14 (MB). This voltage is used for all the operations. In this section +12V is provided from horizontal output section. Transistors QA02, QA03, QA04 (BC558) are used for selecting the desired band from tuner section. To switch on these transistors approximately 10.8 V is provided at their base. Output is obtained at IF terminal (TP20). AGC Voltage (2.8V approximately) is obtained from pin 11 of IC7680 (IC101). This voltage is used for automatic gain controlling purpose. AFT voltage is provided from pin 13 of IC7680. It is available at TP16. Tuning pulse output from system control IC is fed in to the base of transistor Q903 (BC547). Which switches on the transistor and so tuning voltage of 0-33V approximately is obtained at TV terminal (TP19). Following are the various terminal of RF tuner, which are provided in the form of Test Points (TP) in our trainer kit. UB : The system control IC provides the UHF band selection voltage. This voltage switches ON the transistor, hence UHF band is selected. HB : VHF band III selection voltage available from system control IC through switching transistor at HB pin. LB : VHF band I selection voltage is available at LB pin from system control IC through switching transistor. TU : Channel selection voltage is available at this pin through transistor. It varies from 0-33V during channel selection. AGC : Automatic Gain Control voltage is available at this pin from IC7680. AFT : Automatic Fine Tuning voltage is available at this pin from IC7680. MB : It is tuner section's Power Supply pin. Here 12 volt (approximately) is available. IF : Intermediate frequency output signal from tuner is available at IF pin
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ST2651
Figure 2
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ST2651 Experiment 2 Objective: Study of RF section through Test Points TP21 Blue: Tuner section (UB) requires supply of 10.8V approximately if UHF band is selected, otherwise 0V. On selecting the UHF band of system control IC, 10.8V approximately is obtained at pin no. 3 (for other band selection, it is 0V) TP19 Blue: Tuner section (TU) selection 0-8V (approximately varying) during channel. Pin 33 of system control IC provides the tuning pulse output to TV terminal through transistor Q903 (BC547) TP18 Blue: Tuner section (HB) 10.8V approximately, if VHF III band to selected otherwise 0V. On selecting the VHF III band of system control IC feeds VHF III band to switching output from pin no. 2 (10V approximately). So 10.8V approximately is obtained here & (for other band selection it is 0V) TP20 Blue: Tuner section 6.8V approximately (AGC) adjustable, this voltage is used for automatic gain controlling purpose and coming from IC7680. TP17 Blue: Tuner section (LB) requires supply of 10.8V (approximately) if VHF I band is selected otherwise 0V. On selecting VL band System control IC provides at pin 1 (10V approximately). So, 10.8V approximately is obtained & for other band selection it is 0V. TP16 Blue: Tuner section AFT required supply of 5.7V approximately, this voltage is obtained from pin no. 13 of IC7680 for the purpose of Automatic Fine Tuning. TP14 Red: Tuner section (MB) Supply for Tuner section is 11V (approximately). It is obtained from Horizontal Output Section.
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ST2651 TP15 Red: Tuner section (IF) Tuner Output signals according to band selection.
Figure 3
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ST2651 Experiment 3 Objective: Study the fault simulation and step-by-step fault finding procedure of RF section. Fault Insertion: Fault 1: No picture, only low contrast snow on screen. Fault Insertion: Remove the shorting shunt from 2 & 3 pin and place it between pin 1 & 2 of jumpers J1 Symptoms: Even antenna is connected but there is no picture only sound is present with low contrast. Fault Section: Tuner Section Procedure: •
Check power supply at TP14 (MB) of tuner section, it should be +12V if not
•
Then Check +12V supply at TP13 if it is OK
•
Remove the shorting shunt from pin 1 & 2 and place it between pin 2 & 3 of jumpers J1.
Result: Now you should get +12V at TP14. Fault 2: No picture, No transmitting sound. Fault Insertion: Remove the shorting shunt from 2 & 3 pin and place it between pin 1 & 2 of jumper J3 Symptoms: No picture, No sound and tuning is not possible. Fault Section: Tuner Section. Procedure: •
Check the voltage at TP4 (33V approximately) if it is not present then,
•
Track may be open or components are faulty.
•
Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J3.
Result: Now you should get picture with OK sound. Fault 3: No Picture, No transmitting sound. Fault Insertion: Remove the shorting shunt from 2 & 3 pin and place it between pin no. 1 & 2 of jumper J4 Symptoms: No picture, there is only snow on & tuning is not possible Fault Section: Tuner section.
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ST2651 Procedure: •
First check the antenna wire and antenna. If it is properly connected then,
•
Select the auto tuning mode. It starts with VL Band
•
During VL Band tuning period 12V will be obtained at TP-17,
•
During VH Band tuning period 12V will be obtained at TP-18
•
During VHF Band tuning period 12V will be obtained at TP-21, if, it is not present then,
•
Check voltage at collector of transistors QA02, QA03, QA04 it should be 12V, if, it is OK then,
•
Check the voltage at Emitter of transistor QA02, QA03 and QA04, it should be 12V if, it is OK then
•
Transistor may be faulty or track may be open between TP13 and emitter of transistor, QA-02, QA-03, and QA-04.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J4.
Result: Now you should get possible tuning and get picture. Fault 4: VH Band is not selected Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between pin 1 & 2 of jumper J5 Symptoms: No picture, no transmitting sound, only snow, but signal received from antenna in VH band is of good quality. Fault Section: Tuner section. Procedure: •
First check the voltage at TP13, it should be 12V (approximately), if it is not present then
•
Check the voltage at TP18, if it is not present then
•
Check the voltage at transistor QA03, if it is not present then
•
Transistor may be faulty or track may be open between emitter of Transistor QA03 & TP13.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J5.
Result: Now you will get VH Band selected & good picture too.
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ST2651 Fault 5: Picture tilted to one side. Sound OK. Fault Insertion: Remove the shorting shunt from 2 & 3 pin and place it between pin 1 & 2 of jumpers J6 Symptoms: Horizontal shaking is observed in the picture. (AGC preset is at higher side) Fault Section: Tuner section Procedure: •
Vary the preset of AGC. If variation of picture is not found to be OK then.
•
Check the voltage variation by keeping the Test Point at TP20 by varying the preset VR151. If no variation is present, check the preset. If it is proper then.
•
Resistance R105 may be faulty, if it is OK then,
•
Check the continuity between R105 and TP20, if it is not proper then,
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J6.
Result: Proper picture without any shaking symptoms is observed.
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ST2651 Experiment 4 Objective: Study of detail circuit description of VIF section This section includes VIF and SIF sections. This trainer uses IC101 (CD7680) for VIF and SIF sections. The signals at terminal (TP15) of tuner section are fed at the base of transistor Q161 (C388A) through coupling capacitor C161 (01µf). This amplified IF signals are available at collector of this transistor and then fed to Saw Filter through capacitor C163 (.01µf) collector of pre-amplifies transistor gets positive supply by resistances R164 (220Ω) and R165 (470Ω). Base biasing is given by resistance R163 (5.6K) and R162 (1K) to base of pre-amplifier and its emitter is grounded by R166 (27Ω). Output of saw filter is fed to pin no. 7 and 8 of IC101 (IC7680) by coil L102 (TRF 1452) R101 (820Ω) and C101 (.01µf) network. Pin no. 7 & 8 are VIF amplifier pins. The signal from this section is fed to video detector after amplification. Video detector detects line video signal and amplified by video preamplified section. Composite colour video signals are obtained at pin no. 15. The signal is shown at TP23.This composite signal also has SIF signal of 5.5 MHz. Ceramic filter Z106 (5.5 MHz) sets sound IF signals 5.5 MHz through capacitor C7 (68pF). This ceramic filter separates the second IF signal from composite video signal. The filtered sound IF signals are fed to pin no. 21 of this IC sound. IF amplifier section amplifies the sound IF signals and send it to FM detector section where audio signals are obtained. Audio signals are available at pin no. 3 of this IC at pin no. 22 and 24 FM detector circuit is connected with FM detectors coil. Pin no. 1 of this IC gets the volume control signal from pin no. 39 of system control IC through transistor Q901 (BC547). Pin no. 17 and 18 are the pins of video detector section. Here L151 (1445) video detector coil is used. Resistance R108 (3.9K) video detector coil and a capacitor parallel to this coil passes the signal to video detector section for detection. After that the signal reaches to AFT detector section. The detected signals from AFT section are obtained at pin no. 13 which is AFT output pin. AFT signals are fed to AFT terminal of Tuner by resistance R171 (2.7K). From tuner's AFT point this AFT signals are fed to base of buffer transistor Q910A (BC547) which comes out from its emitter. Then the circuit of C196 (4.7KPF) R925 (4.7K) R924 (470Ω) and diode D903 (IN4148) passes this signal to pin no. 15 of system control IC. It is very important to give the signal to system control section because the channels cannot be locked without this signal. AGC voltage is given to AGC terminal of tuner from pin no. 11 of this IC through resistance R105 (220Ω). There is (15K) R151 variable resistance for AGC adjustment.
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ST2651 The IC 7680 incorporates the following functions. a.
Gain controlled wide band amplifier providing complete IF gain.
b.
Video detection.
c.
Video pre-amplification.
d.
AFC detection output providing.
e.
IF AGC and RF AGC
f.
Sound IF limitation and amplification.
g.
FM detection.
h.
Attenuation and providing audio output.
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ST2651
VIF and Sound IF Circuit Figure 4 Scientech Technologies Pvt. Ltd.
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ST2651 Experiment 5 Objective: Study of VIF section through following Test points Pin 3 of IC VIF section: Audio output signal from IC7680 fed to sound amplifier 7 VDC. TP23 Red VIF section: Composite video signal (Pin no. 15 of IC7680).
Figure 5
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ST2651 Experiment 6 Objective: Study of fault simulation and step by step fault finding procedure of VIF section Fault 6: No Sound, No Picture only plane raster on the screen. Fault Insertion: Remove the shorting shunt from 2 & 3 pin and place it between pin 1 & 2 of jumper J2 Symptoms: There is no sound nor picture on the screen. Only plane raster is present. Fault Section: VIF Section Procedure: •
Check power supply at pin no. 20 of IC101 (IC7680) If not then,
•
Check +12V at TP13 if it is OK
•
Then may be track open between TP13 and Pin 20 of IC101
•
If not then check the continuity connection between TP13 and TP6.
•
Remove the shorting shunt from pin 1 & 2 and place it between pin 2 & 3 of jumper J2.
Result: Now you should get +12V at pin no. 20 of IC101.& good picture with sound Fault 7: Plane Raster on the Screen. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between pin 1 & 2 of jumper 31 Symptoms: Only plane raster on the screen without any sound. Fault Section: VIF Section. Procedure: •
First check the composite colour video signal at pin no15 of IC101. If it is OK then,
•
Check the composite colour video signal at pin no. 39 of IC501.
•
The components connected between TP23 and pin no. 34 of IC501 may be faulty. If these are OK then,
•
Check the track between TP23 and pin no. 39 of IC501.
•
Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of Jumper 31.
Result: Now you should get clear picture with sound.
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ST2651 Fault 8: No Picture. No transmitting sound. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between pin 2 & 3 of jumper J37 Symptoms: No Picture, there is only snow Fault Section: VIF Section Procedure: •
First check the antenna wire and antenna. If it is properly connected then,
•
Check the tuner voltage +12V at TP-14. If it is OK then tuner may be faulty.
•
Now try to get the picture with the help of Auto tuning/ Fine tuning. If you are not getting the picture then,
•
Check the +33volt at TP4 DA13. If it is OK then,
•
During the auto mode, check the voltage variation of 0V to 8V at emitter of TR Q902. If it is not varying then,
• •
Track may be track open between DA13 and Q902. Remove the shorting shunt from pin 2 & 3 and connected between 1 & 2 Jumper J37. Result: Now you should get clear picture with sound. Fault 9: Picture with distorted Sound. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between pin 2 & 3 of jumper J7 Symptoms: There is picture with snow and distorted sound. (In case of improper antenna plane raster will appear Fault Section: VIF Section. Note: To find out this problem take signals from colour pattern generator ST2670 instead of antenna. Procedure: •
First check the IF signal at TP15, if it is OK then,
•
Check the IF Signal at TP22. if it is OK then,
•
Check this signal at Base of transistor Q161, If it is OK then,
•
Transistor may be faulty. If it is OK then
•
Now check the IF signal at the end of capacitor C163 connected to saw filter, if it is weak then
•
Check capacitor C163 is connected with ground or not.
•
Remove the shorting of shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J7. Result: Now you should get good picture with OK sound.
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ST2651 Experiment 7 Objective: Study of detail circuit description of Video & CHROMA section Scientech Colour TV trainer ST2651 uses IC CD7698 (IC501) for video & chroma section. Vital part of the IC is used for chroma section. For chroma section pin no. 123 and pin no. 38-42 are used, other pins are used for Video section. For chroma section following are the main sub sections in the IC: •
Chroma amplifier
•
Colour oscillator
•
Colour killer detector
•
Matrix
•
Luminance (Y) signal amplifier.
VIF section IC101 (CD7680) pin no. 15 supplies the composite colour video signal to the inverter pin no. 39 of IC501 (CD7698) by circuit made up of L105 (3.3µH) R958 (330Ω), Trap5.5 MHz (ceramic filter) and L201 (12µH). In inverter section this signal is amplified as well as detected, After detection Y signal goes to Y amplifier which is in built in IC, Remaining amplified composite colour and sink signal are obtained at pin no. 40 of this IC, then fed to pin no. 5 of this IC through resistance R501 (820Ω), C560 (18pF) and C502 (10pF). Pin no. 5 is Band pass amplifier pin. Signal goes to band pass amplifier by this pin and amplified here. Amplified signal is obtained at pin no 8. From pin no. 8 the signal fed to pin no. 19 of this IC by passing it through chroma trap circuit. This trap circuit consists of VR551 (1K) C507 (0.01µf), C508 (15Pf), C502 (10µH) X502 (DL701 delay line), L551 (TRF5418) R510 (470Ω) and C509 (.01µF). From pin no. 8 this signal is also fed to pin no. 17 of this IC in the form of colour sink signal by resistance R509 (1.5K), C510 (.01µF) pin no. 17 is of matrix section. Pin no. 41 is contrast control pin. Pin no. 41 gets the contrast control signal from pin no. 37 of system control IC through resistance R946 (560Ω), R945 (1.5K) and R213 (47K). Pin no. 4 of this IC is brightness control pin. Pin no. 38 of IC901 (system control section) supplies the brightness control signals at this pin through resistance R941 (1K), R956 A (47K), R212 (10K). Pin no. 7 of IC501 (CD7698) receives the colour control signals from pin no. 36 of IC901 through resistance R947 (1K), R942 (12K) and R505 (2.2K). Pin no. 20 of IC501 (CD7698) is output pin of green colour signal. Green colour output signal from this pin is fed to base of green colour amplifier transistor. In the same way red colour signal obtained at pin no. 21 of this IC and then fed to base of red colour output transistor Q507 (C2310). Blue colour signal obtained at pin no. 22 of this IC and then fed to base blue colour output transistor Q509 (C2310).R-Y signals & B-Y signals. Y signals from pin no. 42 of this IC are fed to pin no. 3 of the same IC through resistance R203 (1.5K), R210 (1.5K) arid capacitor C204 (.47µF) circuit network. Luminance signals are out from pin no. 23 of this IC and fed to base of luminance amplifier transistor.
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ST2651 Q202 (2SA 1015) this transistor amplifies the signal and out the signal by its emitter, which is then fed to all the three emitters of three colour output transistors. Pin no. 30 to 37 of IC501 (CD7698) works for horizontal oscillator AFC and sync separator sections.
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ST2651
Figure 6 Scientech Technologies Pvt. Ltd.
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ST2651 Experiment 8 Objective: Study of video & chroma section through following Test Points TP26 Blue
Video & Chroma section
+12V (approximately)
TP28 Blue
Video & Chroma section
Colour composite video signal
Figure 7 TP29 Red
Video & Chroma section
Inverted Colour composite Video signal
TP 31 Red
Video & Chroma section
Luminance Signal.
Figure 8
Figure 9
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ST2651 TP34 Blue TP37 Blue
Video & Chroma section Video & Chroma section
+ 10V (approximately) 4.43 MHz sub carrier frequency
Figure 10 TP38 Blue Video & Chroma section + 12 V (approximately) TP39 Red Video & Chroma section for colour adjustment. To observe Colour burst signal at Pin no. 5 of IC501, connect pattern generator (colour bar pattern) at antenna socket.
Figure 11
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ST2651 Experiment 9 Objective: Study of fault simulation and step by step fault finding procedure of Video & chroma section Fault 10: There is yellow colour on the screen with OK Picture. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J25. Symptoms: There is good picture on the screen with yellow shade colour Fault section: Video & Chroma section Procedure: •
Check pin no. 22 of IC501 (IC7698) it should be + 7.2V approximately. If it is not then IC may be faulty.
•
We know that if there is yellow shade on the screen it means blue colour is absent.
•
Check circuit of pin no. 22 of IC501 (B-Y output) it should be +7.2V approximately at B terminal (Berg strip pin), if it is not.
•
There may be track open between this B terminal and pin no. 22 of IC501.
•
Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J25.
Result: Now you should get picture in normal colours. Fault 11: There is cyan colour on the screen with OK picture. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J24 Symptoms: Sound and picture OK only screen has cyan colour shade Fault section: Video & Chroma section Procedure: •
We know that if there is cyan colour on the screen it means that red. colour is absent
•
Check pin no. 21 of IC501. It should be 7.2V approximately, if not IC may be faulty
•
Check this voltage at R terminal, if it is not then, There may be track open between pin no. 21 of IC501 & R terminal.
•
Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J24.
Result: Now you should get picture with normal colours. Scientech Technologies Pvt. Ltd.
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ST2651 Fault 12: There is magenta shade colour on the screen with OK picture. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J23 Symptoms: Sound and picture OK with magenta shade Fault Section: Video & Chroma section. Procedure: •
We know that if there is magenta colour on the screen it means that green colour is absent
•
Check pin no. 20 of IC501 it should be +7.2V approximately (if not then IC may be faulty) if OK then,
•
Check this voltage at G terminal. If it is not then, There may be track open between pin no. 20 of IC501 & G terminal
•
Remove the shorting shunt from pin 2 & 3 of and connect it between 1 & 2 of Jumper J23
Result: Now, you should get picture with normal colours Fault 13: Dull Coloured Picture Fault Insertion: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J19 Symptoms: There is dull picture (Negative type) on the screen with full colours. Fault Section: Video and Chroma Section Procedure: •
Check the luminance signal at pin no. 23 of IC501. If it is not then IC may be faulty, if it is OK then,
•
Check this luminance signal at base of Q202 (1015). If it is not here then, there may be track open between pin no. 23 of IC501 and base of T202.
•
Replace the shorting shunt from 2 & 3 and connect it between 1 & 2 of Jumper J19.
Result: Turn on the instrument, you should get good picture on the screen. Fault 14: Picture is vertically rolling with OK sound Fault Insertion: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J21 Symptoms: There is OK sound from the trainer kit but picture is vertically rolling. Fault Section: Video and Chroma Section
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ST2651 Procedure: •
Check vertical sync pulse at pin no. 36 of IC501 (CD7698). If it is OK then,
•
Check the pulse at pin no. 28 of IC. If it is not then, There may be track open between these two pins or R330 (30K) or capacitor,
•
Replace the shorting shunt from pin 2 & 3 and connect it between 1 & 2 Jumper J21. Result: Now should get clear picture with sound. Fault 15: No colour variation. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J27 Symptoms: There is good picture without colour variation it means black & white picture. Fault Section: Video and Chroma section. Procedure: •
First check the voltage variation of IC501 at pin no. 7, it should be 3.5V to 6.5V approximately. If it is not then,
•
Check the voltage variation at TP52. If it is OK then, check the continuity of track between TP52 & pin no. 7 of IC501. If no continuity is present, then,
•
Remove the shorting shunt from 1 & 2 connect it between 2 & 3 of jumper J27.
Result: Now you should get colour picture with proper variation. Fault 16: No colour with OK sound. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J28 Symptoms: Good picture without colour when colour control is set to max. Fault Section: Video & Chroma section. Procedure: We know that if there is B/W picture on the screen it means colour burst is absent. •
So first check signal at R501 (820R), there should be composite video signal, if it is OK then,
•
Check the colour brust signal at pin no. 5 of IC501, if it is not present then,
•
There may be track open between IC501 at pin no. 5 and R501 (820R).
•
Remove the shorting shunt from pin 1 & 2 of jumper J28 and connect between pin 2 & 3.
Result: Now you should get colour picture.
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ST2651 Fault 17: No colour with OK sound. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J26 Symptoms: Good picture without colour when colour control is set to max Fault Section: Video and Chroma section Procedure: •
First check the sub carrier frequency 4.43 MHz at TP37. If it is not present then, Crystal may be faulty, if it is OK then, Check the continuity of track of pin no. 13 & 15 of IC501. If no continuity is present then,
•
Remove the shorting shunt from pin 1 & 2 connect it between 2 & 3 of Jumper J26.
Result: Now you should get colour picture. Fault 18: There is blue shade colour picture with OK Sound Fault Insertion1: Remove the shorting shunt from pin no. 1 & 2 and connect it between 2 & 3 of jumper J23 Fault Insertion2: Remove the shorting shunt from pin no. 1 & 2 and connect it between 2 & 3 of jumper J24 Symptoms: Sound and picture OK only screen has blue colour shade. Fault Section: Video and Chroma section. Procedure: •
Check pin no. 21 of IC501 it should be 7.2V approximately, if not present, IC may be faulty
•
Check this voltage at R terminal, if it is not then, There may be track open between pin no. 21 of IC501 & R terminal.
•
Check pin no. 20 of IC501 it should be +7.2V approximately (if not then IC may be faulty) if OK then,
•
Check this voltage at G terminal. If it is not then there may be track open between pin no. 20 of IC501 & G terminal
Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J24 Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of jumper J23 Result: Now proper picture with sound is observed.
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ST2651 Fault 19: There is green colour picture. Fault Insertion1: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J25 Fault Insertion2: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J24 Symptoms: Sound and picture OK only screen has Green colour shade. Fault Section: Video and Chroma section. Procedure: •
Check pin no. 22 of IC501 (IC7698) it should be + 7.2V approximately, if it is not then IC may be faulty.
•
Check circuit of pin no. 22 of IC501 (B-Y output) it should be + 7.2V approximately at B terminal (Berg strip pin), if it is not then, There may be track open between this B terminal and pin no. 23 of IC501
•
Check pin no. 21 of IC501 it should be 7.2V approximately, if not IC may be faulty
•
Check this voltage at R terminal, if it is not then, There may be track open between pin no. 21 of IC501 & R terminal
•
Remove the shorting shunt from pin 2 & 3 place it between 1 & 2 jumper J25, if, it is not proper then,
•
Remove the shorting shunt from pin 2 & 3place it between 1 & 2 of jumper J24
Result: Proper picture with sound is observed. Fault 20: There is red colour shade picture. Fault Insertion1: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J25 Fault Insertion2: Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J23 Symptoms: Sound and picture OK only screen has red colour shade. Fault Section: Video and Chroma section.
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ST2651 Procedure: •
Check pin no. 22 of IC501 (IC7698) it should be + 7.2V approximately, if, it is not then IC may be faulty.
•
Check circuit of pin no. 22 of IC501 (B-Y output) it should be +7.2V approximately at B terminal (Berg strip pin), if it is not then, There may be track open between this B terminal and pin no. 22 of IC501.
•
Check pin no. 20 of IC501 it should be +7.2V approximately (if not then IC may be faulty) if OK then, check this voltage at G terminal. If it is not then, There may be track open between pin no. 20 of IC501 & G terminal.
•
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J25, if it is not proper.
•
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J23.
Result: Proper picture with sound is observed.
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ST2651 Experiment 10 Objective: Study of detailed circuit description of Horizontal Oscillator Section and Horizontal Output Sections Horizontal Oscillator: Pin no. 40 of IC501 (CD7698) supplies the composite sync signal to pin no. 37 (Sync Separator) of this IC through the circuit of R301 (750Ω), R302 (560K), capacitor C301 (1µF), C302 (.01µF), C303 (560PF) R513 (15K) and diode D301 (IN4148). Sync separator section separates the horizontal sync and vertical sync. Horizontal sync signals are supplied to AFC section in built in IC from sync separator section. This horizontal section produces the signal of frequency 15625 Hz. These signals are fed to burst gate inside the IC and also to phase detector section at pin no. 35. At pin no. 35 fly back pulses are supplied from pin no. 10 of EHT through resistance R402 (27K), C402 (.47µF) R403 (3.9K). The phase detector section compares the phase and frequency of horizontal sync pulses and fly back pulses and difference control voltage is produced. This control voltage is responsible for constant frequency 15625 Hz of horizontal oscillator. for controlling the frequency of horizontal oscillator horizontal hold circuit is used which is made up of R410 (15K), R406 (150K), C405 (3KPF) and VR451 (10K). This tuned circuit is connected with pin no.34 of IC7698. On varying the horizontal hold preset the voltage at pin no. 34 is varying which affects the frequency produced by horizontal oscillator. For working of horizontal oscillator section positive supply is given at pin no. 33 of IC7698. Here voltage is supplied from +110V supply by resistance R416 (6K8). When horizontal output section is working then 12V supply is converted in to DC by R448 (6R2, 2W), D408 (BY159) and passed through R30 (3K3) and diode D1 (IN4148) and obtained at pin no. 33 of this IC. Pin no. 30 and 31 are the negative supply pins which are grounded. Horizontal Driver: IC501 gives the Horizontal drive signals at pin no. 32. These signals are fed to the base of Horizontal driver transistor T402 (C2310) through coil L407 (1µH), and resistance R 411 (33Ω). At Collector, amplified signals are obtained. It goes to the primary coil of horizontal driver transformer. From secondary of this transformer signals are fed to the base of horizontal output transistor Q404 (BU508DF). At one end of horizontal driver transformer primary coil, + 110V is supplied by resistance R416A (1.5K) which reach up to the collector of horizontal driver, transistor through the other end of primary emitter of horizontal driver transistor is directly grounded.
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ST2651 Horizontal Output Section: This section includes one transistor and EHT transformer. From secondary of horizontal driver transformer signals are fed to the base of horizontal output transistor Q404 (BU508DF). Its collector gets the positive supply from primary winding pin no. 1 and 5 of EHT transformer and R410A (1Ω, 1W). Its emitter is directly grounded when Q404 gets the signal of frequency 15,625 Hz then it works as a switch, when it is ON then current is flowing through Pin no. 1 and 5 of EHT transformer and for ‘Off’ there is no current. In this way this transistor works as a current supplier for limited time for the time gaps. Because of this time gaps current pulses are also produced. The frequency of these pulses is also 15,625 Hz. EHT works on these current pulses. This induced current in primary produces voltage in secondary coil; this signal is fed to the horizontal yoke coil. The function of yoke coil is electron beam spreading in left and right direction on picture tube screen.
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ST2651
Figure 12 Scientech Technologies Pvt. Ltd.
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ST2651 Experiment 11 Objective: Study of horizontal oscillator and horizontal output section through Following Test Points TP5 Red
Horizontal output section
+110V (approximately)
TP6 Red
Horizontal output section for VIF Section
+12V (approximately)
TP7 Red
Horizontal output section for R-G-B video output section (CRT base PCB)
+185V (approximately)
TP8 Red
Horizontal output section
Filament Voltage 6.3V AC (approximately)
TP27 Red
Horizontal Oscillator part of Video & Chroma IC501
Ident (Sync) signal
Figure 13 TP30 Red
Horizontal Oscillator part of Video & Chroma IC501
Horizontal driver signal
Figure 14
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ST2651 TP35 Red
Horizontal Oscillator part of Video & Chroma IC501
fly back pulse
Figure 15 TP36 Red
Horizontal Oscillator Input for Sync. Separator part of Video & Chroma IC501 (composite colour video signal)
TP40 Blue
Horizontal output
Horizontal blanking pulse
Figure 16
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ST2651 Experiment 12 Objective: Study of fault simulation and step by step fault finding procedure of horizontal oscillator and horizontal output section Fault 21: There is no clear picture on the screen and screen is shaking horizontally. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J11. Symptoms: Clear sound without clear picture. Horizontal shaking is present on the screen. Fault section: Horizontal output section Procedure: •
Check fly back pulse of frequency 15625 Hz at pin no. 35 of IC501 (IC7698) if not then,
•
Check this fly back pulse at resistance R402 (27Kohm) if it is not then, Track may be open between pin no. 10 of EHT and this resistance.
•
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J11.
Result: now you should get fly back pulse of frequency 15,625 Hz at pin no. 35 of IC501 and so good picture with good sound is observed. Fault 22: Dark Screen, (Neither Raster nor snow) No sound Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J12. Symptoms: There is no picture no sound condition even raster or snow are also absent. Fault section: Horizontal output section Procedure: •
First check whether LED for power indication is glowing or not, If it is not then,
•
Check AC mains cord and fuse of trainer kit, if LED is glowing then,
•
Check +110V at TP5 if it is OK
•
If it is not then it may be problem of regulation circuit which should be serviced by service personal only
•
Then check pin no. 33 of IC501 (IC7698) it should be 6.9V approximately
•
Check pin no. 32 of IC501 it should be 15625 Hz (Horizontal frequency) if it is present then,
•
If not then IC501 may be faulty or related circuit may be faulty
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ST2651 •
Check the same signal at R411 (33ohm) it is OK then,
•
Check same signal at base of transistor Q402. If it is not then, Track may be open between base of Q402 and resistance R411.
•
Remove the shorting shunt from Pin 2 & 3 and place it between 1 & 2 of jumper J12.
Result: Now you should get good picture with good sound. Fault 23: Set Dead i.e. Dark Screen Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J22 Symptoms: There is no picture no sound from trainer kit. Fault Section: Horizontal Oscillator Section (part of Video& chroma IC501) Procedure: •
First check whether LED for power indication is glowing or not.
•
If it is not then check AC mains cord and fuse of trainer kit. If it is OK then,
•
Check +110V at TP5 if not then it may be the problem of regulation circuit which should be serviced by service personal only
•
Check 6.9V approximately at pin no. 33 of (IC7698). If it is OK then,
•
Check horizontal frequency at pin no. 32 of IC501 it is 15625 Hz. If it is OK then,
•
If it is not then that may be the fault of IC or related circuitry
•
Check this signal at base of Q402, if it is not then,
•
Track may be open between pin no. 32 of IC501 and base of Q402.
•
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J22.
Result: Now you should get picture & sound both from the trainer kit. Fault 24: Horizontal sync out Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J20 Symptoms: Horizontal sync is not adjustable (Preset VR451) Fault Section: Horizontal Oscillator
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ST2651 Procedure: •
Check the signal at pin no. 39 of IC501 If it is OK then,
•
Check the inverted video signal at pin no. 40 of IC501, If it is OK then if it is not then IC may be faulty
•
Check the video signal at pin no. 37 of IC501. If it is not then IC may be faulty.
•
If it is OK then components connected between pin no. 37 and 40 of IC501 are faulty. If these are OK then,
•
Track may be open between pin no. 37 and 40 of IC501.
•
Remove the shorting shunt from pin 2 & 3 and connect it between 1 & 2 of Jumper J20.
Result: You should get clear picture. Fault 25: Dark Screen & OK Sound Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J15 Symptoms: Power indicators are glowing & all voltages are OK, but No picture sound. is OK. Fault Section: Horizontal Output Section. Procedure: •
Check the voltage at TP3 & TP5 (110V DC approximately). If it is OK then,
•
Check the voltage at TP34 (8V approximately). If it is OK then,
•
Check the voltage at TP7 (185V DC approximately).
•
If the above mentioned voltages are present, then EHT is working properly.
•
Check the filament voltage at TP8 (6.3V AC approximately). If it is present.
•
Either CRT may be faulty or the connection between CRT (Pin no. 9) & TP8 is open.
•
Remove the shorting shunt between 2 & 3 & connect it between 1 & 2 of jumper J15.
Result: Now you should get Raster/snow and sound. Fault 26: Dark Screen. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J13 Symptoms: Power indicator is glowing, but no picture & no transmitting sound. Fault Section: Horizontal output section.
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ST2651 Procedure: •
Check the voltage at TP3 it should be 110V DC(approximately) if it is OK then,
•
Check the voltage at TP5 it should be 110V (approximately), if it is not there then. Check the voltage at TP34 8V approximately if it is not present then,
•
It means horizontal output section is dead & there may be open track between TP3 & TP5.
•
Remove the shorting shunt from 2 & 3 connect it between 1 & 2 of jumper J13.
Result: Now you should get picture & sound. Fault 27: Negative type picture (dull picture) Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J14 Symptoms: Picture without contrast. Fault Section: Horizontal output section. Procedure: •
Check the voltage at TP7; it should be 180V DC approximately If it is not then,
•
Check the voltage at D406, it should be 180V approximately If it is OK then,
•
There is no continuity of track between D406 & TP7
•
Remove the shorting shunt from 2 & 3 connect it between 1 & 2 of jumper J14.
Result: Now you should get proper picture. Fault 28: Retrace line on picture. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J16 Symptoms: Picture and sound OK. But retrace line on the picture Fault Section: Horizontal output section. Procedure: •
Check the luminance signal at pin no. 23 of IC501it should be 6 Vpp, if it is not present then,
•
Check the vertical blanking pulses at D202. If it is not present then, It means signal is present without blanking pulses or the components between TP31 and D202 are faulty or track may be open.
•
Remove the shorting shunt from 2 & 3 and connect it between 1 & 2 of jumper J16.
Result: Now you should get picture without retrace.
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ST2651 Experiment 13 Objective: Study of detail circuit description of vertical oscillator and vertical output section Vertical Oscillator: Vertical oscillator is also built in IC501 (CD7698) & pin no. 24, 25, 26, 27, 28, 29 are its connection pins. As we have already studied that vertical sync signal is present at pin no. 36 after sync separation. The vertical sync signal from pin no. 36 passes from circuit network of R304 (10K), R330 (3K), R305 (2.4K) and capacitor C310 (.47µF) and obtained at pin no. 28. Vertical oscillator produces 50 Hz frequency which is amplified inside the IC and available at pin no. 24 which is vertical driver pin. This vertical driver signal from pin no. 24 is fed to base of vertical driver transistor Q303 (C2229) by resistance R325 (330Ω). Collector of this transistor provides amplified output which is supplied to vertical output section for amplification. Vertical Output: Vertical driver signal is given to the vertical output section. In vertical output section two push-pull transistors are used. One is NPN transistor Q306 (C2073) and another one is PNP transistor Q307 (A940). Vertical signal from the collector of vertical driver transistor Q303 (C2229) are fed to the base of both vertical output transistors Q306 and Q307. Pin no. 8 of EHT transformer provides the positive supply to vertical output section. There is approximately 36V AC at pin no. 8 of EHT transformer. It is rectified by R327 (10Ω, 2W) and diode D302 (BY159) and supplied to vertical output section by R355 (27R) and R317 (680Ω). Capacitor C311 (330µF) is filter capacitor of this supply. Amplified signal after amplification is obtained at common point of both the emitters of both vertical output transistors Q306 & Q307. This signal is fed to vertical yoke coil by capacitor C316 (330µF).Other end of vertical yoke coil is grounded by resistance R323 (1R8, 1W). The same end of vertical yoke coil provides the vertical feedback to pin no. 26 of vertical oscillator section by C317 (4.7µF / 63V) and R321 (1KΩ) Vertical Height Control: At pin no. 27 of IC501 (CD7698) vertical height control is connected. VR225 (47K) is vertical height adjustment preset and from its centre point vertical linearity preset is connected which is VR316 (10K).
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ST2651
Figure 17
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ST2651 Experiment 14 Objective: Study of vertical oscillator and vertical output section through following Test Points TP11 Red
Vertical Output
V Yoke
TP12 Red
Vertical Output
V Yoke
TP32 Red
Vertical oscillator Part of video & Chroma IC
Vertical feedback
Figure 18 TP33 Blue
Vertical Oscillator Part of Video & Chroma IC
Vertical driver
Figure 19 TP41 Red
Vertical output section
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+17 V (approximately)
50
ST2651 Experiment 15 Objective: Study of fault simulation and step by step fault finding procedure of vertical Oscillator and vertical output section Fault 29: There is Horizontal Line on the screen. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J18 Symptoms: No picture OK sound. Only Horizontal line is present on the screen. Fault Section: Vertical oscillator (part of video & chroma IC501) Procedure: •
Check vertical frequency of 50 Hz at pin no. 24 of IC501 (IC7698) if it is OK then,
•
If it is not then IC or related circuit may be faulty
•
Check this signal at base of transistor Q303, if it is not then
•
Faulty R325 or track may be open between pin no. 24 of IC501 and base of Q303.
•
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J18.
Result: Now you should get picture on the screen. Fault 30: Bottom fold over the picture on the screen. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J17 Symptoms: The 90% of picture screen is OK only bottom side 10% picture is folded over on the original picture. Fault Section: Vertical output Section. Procedure: •
Check output of the vertical driver pin no. 24 of IC501 It is vertical frequency of 50 Hz. If it is OK then,
•
Check output of vertical output section at R333 (1R). It should be amplified signal. It is not correct then,
•
Faulty components in its circuit or ground may be open.
•
Check R313 (15K) and its ground connection.
•
Remove the shorting shunt from pin 1 & 2 and connect it between 2 & 3 of jumper J17.
Result: Now you should get clear picture.
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ST2651 Experiment 16 Objective: Study of detail circuit description of R-G-B Video output Section The R-G-B output section mainly uses three transistors. First one is Q507 (C2310) for red colour output. Second one is Q508 (C2310) for green colour output and third one is Q509 (C2310) used for blue colour output. Red colour signal produced from pin no. 21 of IC501 (CD7698) and fed to the base of transistor Q507. Amplified signal from this transistor are given to the red cathode pin no. 8 of picture tube by resistance R901 (4.7K). Green colour signal from pin no. 20 of IC501 are fed to the base of transistor Q508 from where it is amplified and comes out from its collector. This amplified green colour signal is given so the green cathode pin no 6 of picture tube by resistance R902 (4.7K) In the same way blue colour signal from pin no. 22 of IC501 are fed to the base of transistor Q509 amplified signals are obtained at its collector from where the signal is given to the blue cathode pin no. 11 of picture tube by resistance R903. (4.7K) Collectors of all the three output transistors gets the +185V supply from pin no. 2 of EHT transformer. Red colour output transistor Q507 gets it by resistance R591 (15K 2W) green colour output transistor Q508 gets it by resistance R592 (15K 2W) and blue colour output transistor gets this supply by resistance R593 (15K 2W) Green colour and blue colour output transistor has 220Ω preset connected with their emitters for proper alignment of colour on screen, actually by doing this we are changing the amplification of transistors.
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ST2651
Figure 20
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ST2651 Experiment 17 Objective: Study of detail circuit description of sound output section Scientech colour TV trainer ST2651 uses most commonly used sound amplifier ICTDA 2611. In our circuit it is IC601. As we have already studied that audio signals are available at pin no. 3 of IC101 (CD7680)-which is supplied to base of audio amplifier transistor Q601 (2SA 1015) by capacitor C608 (10µF/63V) Resistance RS1 (10K), R102 (2.2K). Collector of transistor Q601 (25A1015) gives amplified signals. This amplified signal is fed to pin no. 7 of sound output by resistance R605A (4.7K) and C605 (.1µF).Audio signals are amplified up to the sufficient level by this IC and obtained at pin no. 2 of this IC. It is provided to speaker by a capacitor C601 (470µF, 16V), pin no. 1 of IC601 is positive supply pin. SMPS transformer in power supply section provides AC voltage from pin no. 2 which is rectified by diode D810 (BY159) 22V approximately voltage is obtained which is given to pin no. 1 of IC1601 (TDA2611).Pin no. 4 of IC601 is grounded. Other pins 3, 5 and 9 are no contact pins or not connected pins.
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ST2651 Experiment 18 Objective: Study of fault simulation and step by step fault finding procedure of Sound Output Section Fault 31: There is no sound from speaker. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J9 Symptoms: Good Picture on the screen but without sound. Fault Section: Sound Section. Procedure: •
Check power supply +20V at pin no. 1 of IC601 (IC2611) if it is OK then,
•
Check audio input signal at pin no. 7 of IC601 it should be low gain audio signal. If it is OK then,
•
Check audio output signal at pin no. 2 of IC601 it should be amplified audio signal. If it is OK then,
•
If it is not then IC may be faulty
•
Check this amplified audio signal at speaker pin (connected with speaker)
•
If it is not then track may be open between IC601 (pin no. 2) and speaker pin, if it is OK then speaker may be faulty.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J9.
Result: Now you should get (sound) audio signal from speaker. Fault 32: No sound but good picture. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J10 Symptoms: Sound is not present but good picture. Fault Section: Sound section.
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ST2651 Procedure: •
First check the speaker, if it is OK then,
•
Check the voltage of IC601 at Pin no. 1 it should be 20V approximately, if it is not present then,
•
Check the voltage of D810 it should be 20V approximately If it is OK then,
•
Check the continuity of track between D810 & IC601 at pin no. 1 if no continuity present then,
•
Remove the shorting shunt between 1 & 2 connect it 2 & 3 of jumper J10.
Result: Now you should get sound. Fault 33: Very low sound. But ok picture. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J8 Symptoms: Sound is not varying by the volume control but OK picture. Fault Section: Sound section. Procedure: •
First check the audio at the base of Q601 by touching any metallic thing like screw driver.
•
Check the SIF signal of IC101 at Pin no. 3, if it is OK, then
•
Check SIF signal at Base of transistor Q601, if it is not then
•
Transistor may be faulty or track may be open between Pin no. 3 of IC101 and Base of Transistor Q601
•
Remove the shorting shunt between 1 & 2 and connect it 2 & 3 jumper J8
Result: Now you should get volume variation.
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ST2651 Experiment 19 Objective: Study of detail circuit description of AV section AV section is used for hearing audio signals or watching the video signals from external source like VCR or VCD or DVD. CD players available in market mostly supply Audio-Video output signals that can be seen/hear only on that television set which have the facility of AV section. If the television set does not have this facility then there is need of conversion of AV signal to RF signals with the help of converter. For using AV facility we have to press AV switch on remote. There will be plane raster on the screen and “AV” will be displayed on the screen. It means trainer is now ready to accept input signals from AV socket and hence the RF signals present on RF input socket from antenna are disconnected. Pin no. 4 of IC901 (System Control Section) provides AV signals at the base of transistor Q702 (CI815/BC547) by a diode D704 (IN4148) as the transistor gets the signal on its base it starts conducting and hence there is negative voltage on collector of the transistor. This negative voltage is fed to pin no. 21of IC101 (CD7680) by diode D702 (IN4148). It is input pin of sound IF. This voltage stops the sound IF signals entry at IC. In the same way this negative voltage is also fed to the pin no 5 of IC7680 by a diode D703 (IN4148) this pin is video amplifiers pin due to this voltage video signals are unable to go in forward sections, so on selecting AV mode there is plane raster on the screen with sound mute. Now on connecting VCR/VCD AV input sockets the signals from VCR/VCD can be seen on the screen. Video Signals IN: Video signal obtained from VCR/VCD is fed to the base of video signal amplifier transistor Q705 (C1815) by a capacitor C707 (47µfd) and diode D705 (IN4148). Amplified signals come out from its emitter and are provided to TRAP (5.5 MHz) filter. Pin no. 39 of IC501 (CD7698) gets biasing by resistance R716 (8.2K) collector of Q705 gets the biasing voltage by a regulator transistor Q704 (BC558). Audio IN: Audio signals supplied by VCR/VCD/DVD are fed to the base of transistor Q703 (C1815) by capacitor C703 (.15µf) collector of the transistor provides amplified audio signals. These amplified signals are fed to the base of Q701 (1815) through capacitor C704 (1µf) R704 (IK), C701 (2.2µf) and diode D701 (IN4148). Its emitter provides the amplified signals. The amplified audio signals are supplied to pin no. 23 (FM detector pin) of IC101 (CD7680) by capacitor C702 (1µf) and R706 (5.6K). Both the above transistors get the biasing from voltage regulator transistor Q704 (BC558).
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ST2651
Figure 21
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ST2651 Experiment 20 Objective: Study of fault simulation and step by step fault finding procedure of AV Section Fault 34: No sound in AV Mode But good picture. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J30 Symptoms: Signal fed in audio/video socket from VCR/VCD is OK, but no sound. Fault Section: AV section Procedure: •
Check the cable connectivity between VCR/VCD and input socket of TV trainer. If it is OK then,
•
Check the sound signal coming from VCR/VCD by oscilloscope.
•
Check the audio signal at the base of Q702, if not
•
Then the capacitor C703 (.15µF) may be faulty or track may be open between capacitor & the transistor base.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper. J30
Result: Now you should get sound Fault 35: Video is not coming but proper sound. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J29 Symptoms: Signal fed in audio/video socket from VCR/VCD is OK, but no picture. Fault Section: AV Section. Procedure: •
Check the cable connectivity between VCR/VCD and input socket of TV trainer
•
Check the video signal coming from VCR/VCD by oscilloscope
•
Check this signal at base of transistor Q705, if it is OK then
•
Check Video signal at Resistor R958, if it is not present then,
•
Transistor may be faulty or track may be open between R958 and Base of transistor Q705.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J29.
Result: Now you should get picture.
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ST2651 Fault 36: While selecting AV mode plane raster with mute sound which should be there is not present. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J39 Symptoms: Snow added picture is observed on the screen Fault Section: AV Section Procedure: •
Select the Trainer in AV mode.
•
Check the voltage of IC901 at pin no. 4. It should be 1.8V approximately If the present voltage observed is 5V approximately
•
Proper voltage 0.650V approximately should be present on pin no. 5 & pin no. 21 of IC101. If not,
•
Diode D702/703 may be faulty. If not,
•
Check the continuity between D704 & IC901 (Pin no. 4). If continuity is not present then,
•
Remove the shorting shunt from 2 & 3 and connect it between 1 & 2 of jumper J39.
Result: Plain, raster & mute sound is obtained. in AV mode
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ST2651 Experiment 21 Objective: Study of detail circuit description of System Control Section Scientech colour TV Trainer ST2651 uses IC901 FONDA4ST for system control purpose. It is dual in line package 40 pin IC which controls all the sections of the TV Trainer. Pin no. 1, 2 and 3 are band switching pins. 1st pin is used for switching the VL band. Second one is used to switch VH band and third pin is for UHF band Pin no. 4 provides TV/AV switching signals on pressing the AV switch from remote control, the RF signals coming from antenna or cable are disconnected with VIF section. Hence there is only raster on the screen without snow. Pin no. 5, 6, 7, 21, and 22 are the key matrix pins, which are connected with keyboard. Keyboard is used for selecting one function from front panel. Pins 8 & 9 are the on screen display oscillator pins. Horizontal and vertical sweep frequencies are obtained in these pins with the help of ON screen display oscillator. These frequencies (signals) play an important role for getting ON screen display (OSD) on the screen. The coil connected on pin no. 8 & 9 decides the frequency of Internal Oscillator. These horizontal and vertical sweep frequencies are synchronized with horizontal and vertical blanking pulses. Pin no. 11 & 12 are memory input and output pins. Pin no. 11 is connected with pin no. 5 of memory IC902 and pin no. 12 is connected with pin no. 6 of this memory IC. Whenever we store any channel or put it into memory then these memory signals are stored in memory IC with the help of these pins. Therefore whenever the stored channel is required, memory IC feeds it to system control IC. Pin no. 13 is horizontal blanking input pin. Pin no. 14 is vertical blanking input pin. Pin no. 15 is AFT (Automatic Fine Tuning) input pin. IC101 (7680) pin no. 13 provides AFT voltage to pin no. 15 of system control IC through buffer transistor Q910A (BC547) .This AFT signal is important while channel locking. Pin no. 24 is reset input pin. It is an active low pin for resetting a transistor Q910 (BC558B) is used Pin no. 25 & 26 are VCO (Voltage Control Oscillator) pins. Here a 4 MHz crystal is connected. A particular value of frequency is created here with the help of 4 MHz crystal of voltage controlled oscillators inside the IC This signal of particular frequency is converted in to function operating signal inside the IC and comes out from IC by key signal output pins. Pin no. 27 is Indent Input (Transmission Identification) pin. Pin no. 28 is stand by input pin, power ‘On/Off’ signals are obtained here Pin no. 29 is OSD blanking output signal pin. The signals on this pin are fed to the base of OSD blanking driver transistor Q908 (BC558B). After amplification from this transistor these signals are fed to the base of other OSD blanking driver transistor Q908 (BC558B). From where the signals are out from its collector and fed to the base of luminance amplifier transistor Q202 (2SA 1015).
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ST2651 Pin no. 30 is output pin of green OSD signals. The signals from this pin are fed to base of green OSD driver transistor Q906 (BC547B) and then to the base of green OSD output transistor Q1 (2SC1815). The output of this transistor is fed to the emitter of (G-drive) green colour output transistor Q508 (C2310). Pin no. 31 is output pin of red OSD signal. These red OSD signals are fed to the base of red OSD driver transistor Q905 (BC547B). After amplification these signals are fed to red OSD output transistor Q2 (2SC1815) from emitter of previous transistor. The amplified signals are obtained at collector of Q2 and are given to the emitter of red output transistor Q507 (C2310). Pin no. 33 is tuning pulse output pin the signal from this pin switches ON the tuning pulse switching transistor to get the 0-33V at TV terminal. Pin no. 34 is Infrared remote input pin ON pressing the remote switches. The signals are obtained first at this pin for any function from remote switch; remote provides infra red waves, which falls on sensor EYE on front panel. This eye recognizes the signal and amplifies it and gives to pin no. 34 of this IC. So the signals work inside the IC for which remote key was pressed. Pin no. 36 is colour control pin. The colour control signals are fed to pin 7 of IC501 (7698). Pin no. 37 is contrast control pin. The contrast control signals are fed to pin 41 of IC7698. Pin no. 38 is brightness control pin. The signals from this pin are fed to pin no. 4 of IC7698. Pin no. 39 is volume control pin. The volume control signals from this pin are supplied at the base of transistor Q901 (BC547 - Volume Control Transistor). The signals from the collector of this transistor are given to the signal input pin no. 1 of IC7680. Pin no. 40 is +5V supply pin. Output of IC102 (L7805) is directly connected on this pin. Pin 16, 19, 20 are ground pins. Pin no. 17, 18, 23 are Bias pins. The Biasing is provided from +5V supply. Pin no. 32 & 35 are no connection pins.
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ST2651
Figure 22
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ST2651 Experiment 22 Objective: Study of system control section through following Test Points TP24 Blue
+ 18V (approximately)
TP25 Red
+ 5V (approximately)
TP42 Red
System Control Section 9V approximately from system control IC to select VHF I band (VL) otherwise 0V.
TP43 Red
System control Section 0V when VHF III (VH) band selected otherwise 9V approximately
TP44 Red
System control Section 0V when UHF band selected otherwise 9V approximately
TP45 Blue
System Control Section Horizontal blanking pulse input for system control IC.
Figure 23 TP46 Blue
System Control Section Input for system control IC
Vertical blanking pulse.
Figure 24
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ST2651 TP47 Blue
System Control Section
Input for AFT 3.2 VDC (approximately)
TP48 Blue
System Control Section
Ident signal 0.2-5 VDC (approximately)
TP49 Red
System Control Section
Input pin for standby Mode +5V when power is ON otherwise 0V
TP50 Red
System Control Section
Output of tuning signal 5Vpp approximately
TP51 Blue
System Control Section
TP52 Red
System Control Section
+5V approximately Infrared signal from Remote Colour control pin 0.2-8V approximately
(Middle position of colour control) Figure 25 TP53 Red
System Control Section
Contrast control pin 6-10V approximately
Figure 26
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ST2651 TP54 Red
System Control Section
Brightness control pin 0.4 - 9V approximately
(Middle position of Brightness control) Figure 27 TP55 Red
System Control Section
Volume control pin 0.2 - 4V approximately
(Middle position of Volume control) Figure 28
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ST2651 Experiment 23 Objective: Study of fault simulation and step by step fault finding procedure of system control section Fault 37: Set Dead Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J32 Symptoms: There is no picture nor sound neither raster/snow. Fault section: System control section Procedure: •
First check whether LED for power indication is glowing or not, if it is not then,
•
Check 110V at TP3 if it is OK
•
If it is not then it may be problem of regulation circuit which should be serviced by service personal only
•
Then check pin no. 33 of IC501 (IC7698) it should be 6.9V approximately then,
•
Check power supply of system control IC901 (Fonda 4ST) at pin no. 40 it should be +5V, if it is OK then,
•
Check pin no. 26 of IC 901 for signals of 4 MHz frequency, if it is not then,
•
Track may be open between crystal of 4 MHz and pin no. 26 of IC901 or crystal may be faulty or IC901 may be faulty.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J32.
Result: Now you should get picture with sound. Fault 38: No volume variation Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J33 Symptoms: There is good picture without sound variation facility. Fault section: System control section Procedure: •
Check ident signal on pin no. 27 of IC901 (Fonda 4ST) if it is not then (Check only with oscilloscope)
•
Check this signal at collector of transistor Q909 if it is not here then,
•
Check it at the base of same transistor if it is not here then,
•
Transistor may be faulty or track may be open between pin no. 27 of IC901 and collector of transistor Q909.
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ST2651 •
Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J33.
Result: Now you should get volume variation when operated. Fault 39: Remote control is not working. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J34 Symptoms: Remote control functioning/working is totally ‘Off’ Fault section: System control section Procedure: •
Check IR(Infrared )signal +5V approximately at TP51, if it is not then
•
Check the same IR signal at IR terminal (Berg strip) if it is OK then
•
Track may be open between IR terminal and TP51
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J34.
Result: Now remote control can be used Fault 40: No contrast Variation Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J35 Symptoms: Contrast variation is not working. Fault section: System control section Procedure: •
Check pin no. 37 (contrast control pin) of IC901 (Fonda 4ST) Now, if you vary the contrast from remote the voltage at this point should vary from - 6mV to +2.1V approximately, if it is OK then
•
Check pin no. 41 of IC501 (IC7698) & vary the contrast from remote you should get approximately 1V variation from its present voltage. If it is not then
•
Track may be open between pin no. 37 of IC901 and pin no. 41 of IC501
•
Remove shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J35
Result: Now you should get contrast variation Fault 41: No Brightness variation Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J36 Symptoms: No variation in brightness but good picture & sound.
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ST2651 Fault section: System control section Procedure: •
Check pin 38 of IC901 (Fonda 4ST) while varying the brightness here voltage varies from 1.9mV to 2.6V approximately If it is OK then
•
Check pin 41 of IC501 (IC7698) and vary the brightness you should get the voltage variation from 7.3 to 6.9V approximately if it is not then
•
Track may be open between pin 41 of IC501 and pin 38 of IC901.
•
Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J36.
Result: Now you should get brightness variation. Fault 42: Trainer is Dead. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J43 Symptoms: No picture, No sound and no power indication . Fault Section: System control section. Procedure: •
First check the AC mains supply, if it is connected properly then
•
Check the voltage at TP24 19V approximately, if it is not then
•
Check the voltage at TP25 5V approximately ,if it is not present then
•
Check the same voltage at R980 (150R) if it is not OK then
•
Check the continuity of track between TP24 & R980 (150E). If no continuity is present
•
Remove the shorting shunt between 2 & 3 connect it between 1 & 2 of jumper J43.
Result: Now proper picture with sound is observed. Fault 43: Trainer is dead Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J41 Symptoms: No picture, No sound and no power indication Fault Section: System control section.
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ST2651 Procedure: •
First check the AC mains supply, if it is OK then
•
Check the voltage at TP24 19V approximately, if it is OK then
•
Check the voltage at TP25 5V approximately, if it is OK then
•
Check the same voltage 5V approximately of IC909 at pin no. 40, If it is not present then
•
Check the continuity of track between TP25 & pin no. 40 of IC901.If no continuity is present then
•
Remove the shorting shunt between 1 & 2 connect it between 2 & 3 of jumper J41.
Result: Now proper picture with sound is observed. Fault 44: Very low sound. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 1 & 2 of jumper J38 Symptoms: No variation in sound Fault Section: System control Section. Procedure: •
Check the voltage variation at the collector of the transistor Q901. It will be between 3.19V to 4.60V approximately If this variation of voltage is not present then
•
Check the voltage at TP55 while varying the volume control. Variation of voltage level is noticed between 17 mV & 4.6V but still there is no change in sound then,
•
Check the continuity of track between TP55 & Q901 (BC547). If continuity is not present then
•
Remove the shorting shunt between 2 & 3 and connect it between 1 & 2 of jumper J38.
Result: Now you should get good, full sound & full volume variation. Fault 45: Trainer is dead. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J44 Symptoms: No picture, No sound, but power indication is glowing. Fault Section: System control Section.
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ST2651 Procedure: •
First check the voltage at TP25, 5V approximately should be obtained. If it is OK then
•
Check the voltage of IC901 at pin no. 40, 5V approximately should be obtained. If it is OK then
•
Check the voltage drop at the diode D904, It should be 3.8V (approximately). If not,
•
Diode may be faulty. If the diode is proper then
•
There is a possibility of the resistance R975 to be open. If it is not so then,
•
Check the continuity of track between R975(470R) & D904(3V8) If continuity is not present then,
•
Remove the shorting shunt between 2 & 3 connect it between 1 & 2 of jumper J44.
Result: Now good picture & sound is observed Fault 46: Memory/Store problem. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J40 Symptoms: Memory storage function (Language selection mode etc). Fault Section: System control Section. Procedure: •
The components connected between IC901 & IC902 may be faulty. If it is OK. One or both the IC’s may also be faulty, if it is not proper then
•
Check the continuity of track between IC901 pin no. 11-12 & IC902 pin no. 56. If it is not present then
•
Remove the shorting shunt between 1&2 and connect it between 2 & 3 of jumper J40.
Result: Now memory storage functions will function Fault 47: Auto tuning is not possible. Fault Insertion: Remove the shorting shunt from pin 2 & 3 and place it between 1 & 2 of jumper J45 Symptoms: Tuning will not work properly in Auto Mode (AFT signal not present) Fault Section: System control Section.
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ST2651 Procedure: •
Check the voltage of IC101 at pin no. 13.If it is 6V approximately then
•
Check the voltage at the base of transistor Q910A. It should be 6V approximately If it is not present. Transistor is faulty or else,
•
The components are faulty & no continuity of track between Q910A (Base) and IC101 and pin no 13
•
Remove the shorting shunt between 1 & 2 and connect it between 2 & 3 of jumper J45.
Result: Now tuning will function properly and picture is obtained. Fault 48: OSD is not present. Fault Insertion: Remove the shorting shunt from pin 1 & 2 and place it between 2 & 3 of jumper J42 Symptoms: Picture & sound OK but not getting OSD. Fault Section: System control Section. Procedure: •
Check the vertical Blanking pulse at TP46 ,if it is OK then
•
Check the Horizontal Blanking pulse at TP45, if it is not present then
•
The components are faulty and no continuity of track for horizontal blanking pulses.
•
Remove the shorting shunt between 2 & 3connect it between 1 & 2 of jumper J42
Result: Now there should be OSD.
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ST2651 Experiment 24 Objective: Study of detail circuit description of Switched Mode Power Supply (SMPS) section The trainer has SMPS Power Supply. It outputs are +110V and +22V mainly. AC mains supply is fed to input of line filter L1210 through ‘On-Off’ switch. The main function of line filter is to prevent the spikes present in 50 Hz AC supply for the purpose of safety of trainer kit. Output of line filter is connected with degaussing coil through PTC R802 is connected around the picture tube. When switching ON the TV trainer the degaussing coil gets the supply and demagnetize the picture tube. Bridge rectifier (D806, D807, D808, D809 all are IN4007) is connected with output of line filter. A filter capacitor C815 (100µf. 450V) is connected between positive and negative terminal of bridge which rectifies the DC properly. Negative end of bridge is connected with ground by a resistance R805 (2.2Ω/1W) is called floating ground. This floating ground is connected with main chassis ground by a resistance R829 (10M/0.5W). There is 150 VDC on floating ground with respect to main ground. In the same way there is approximately 300 VDC at positive point of bridge with respect to floating ground. Due to this there is 450 VDC voltage at positive of bridge with respect to chassis ground. So while testing SMPS section we have to always connect negative of multi-meter with floating ground and for testing of other circuits main ground is used. Note: Never short floating ground with main chassis ground, it may damage the circuit. The Power Supply section uses 4 transistors in the circuit Transistor Q801 (C1815)
-
Error Detector
Transistor Q802 (2SA1015) -
Error Driver - 1
Transistor Q803 (C1815Y)
Error Driver - 2
-
Transistor Q804 (BD508AF) -
Switching Transistor
Q802 and Q803 are used to control the duty cycle of Q804. Both these transistors are working as complimentary transistors and get the required supply from pin no. 8 of SMPS transformer for functioning. According to output voltage at secondary of SMPS transformer Q801 is used to change the duty cycle. Zener diode D811 (8.2V) is used to stabilize the voltage of emitter when input voltage is varying or fluctuating the base voltage of Q801 is also changing so that its collector voltage is changing which changes the base voltage of both Q802 and Q803. Emitter voltage of Q801 changes the condition of Q804 and makes the output voltage constant. Positive voltage from bridge is supplied at collector of Q804 through the winding connected at pin no. 1 & 5 of SMPS transformer. The winding connected at pin no. 7-8 & 9-10 gets the feedback voltage. Pin no. 4 of SMPS transformer is connected with chassis ground. Pulse produced by winding connected at pin 4 & 2 of SMPS transformer is rectified by diode D810 (BY159). Output of diode +22V is available which is connected with other circuitry sections in following manner.
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ST2651 •
Pin no. 1 of IC TDA2611 is connected with it by a resistance R601 (6.1Ω/1W).
•
Input of IC102 (LM7805) is connected with it by, a resistance R980 (150Ω/1 W).
•
Relay (+12V) gets this supply by a resistance R610 A (68Ω/1W).
•
When we switch ON the power switch +22V supply is produced without using the power switch of remote. Pulses produced at pin no. 3 & 4 of SM transformer are connected with R610 (1Ω/1W) and R610 B (100K) R610B is grounded and other end is connected with N/O (Normally open end) of +12V relay. When we switch ON the power, relays pole is connected with no terminal and pulses are then rectified by D602 (BY159) and filtered by C810 A (100µf/160V) +110V output voltage is obtained. This +110V is used in other circuitry part in following manner.
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At +110V line a resistance, RA02 (15K) is, connected its other end is connected with DA13 (Z33V) zener diode. This +33V supply is filtered by CA04 (1µf/63V). It is used for TV terminal at tuner.
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+110V is supplied to primary of T401 of horizontal driver transformer by R416A (2K2).
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It is connected with pin no 3 of EHT transformer by a resistance R224 (1Ω/ 1W).
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Horizontal hold resistance gets this supply by a resistance R451 (10K). Also base biasing is given to horizontal driver transistor Q402 by resistance R408 (1.8K), R411 (33Ω).
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Pin no. 33 of IC501 (CP7698) (Horizontal Oscillator Section) gets +110V supply by a resistance R416 (6K8 5W).
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ST2651
Figure 29
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ST2651 General Details for Servicing Set Dead, AC Fuse F1210 Blows ‘Off’: Mains wire, ‘On-Off’ switch, C811 (100KpF), line filter LI 210, degaussing coil D806-D809 (4 x 1N4007) C811A-C812-C812A-C813-C813A (4 x 4K7pF) C815 (100MFd/400V), Q804 (BU508AF) & related parts, check entire power supply section. Set Dead, No Output From Power Supply: Mains wire, ‘On-Off’ switch, F1210 (3.15A), L1210, R826 (4.7Ω/10W), D806-D809 (4x 1N4007), C815 (100MFd/400V), R804-803 (220K), R816 (3.3Ω/2W), R805 (3.3Ω) 0804 (BU508AF), R815 (27Ω/2W), C808 (0.lMFd), D803A-D804 (BY159), C807 (100MFd), R824 (12Ω/1W), Q803 (C1815), Q802 (2SA1015), D803 (BY159), C806 (10MFd), Q801 (C1815) & related parts T801 (rare), check secondary side of T801 & check for Stand by. Switching Transistor Q804 (BU508AF) Overheats or Blows ‘Off’: Q804 (BU508AF) & its mica C810 (IKpF),C803 (1KpF),C815 (100MFd/400V), D606-O809 (1N4007), C807 (100MFd), 0804-D803A (BY159),C808 (0.lMFd),Q803 (C1815),Q802 (2SA1015),D802 (9.lV-zener) D801 (8.W-zener), D803 (BY159), C806 (10MFd),Q801 (C1815) & related parts,T801 (rare), check secondary side of T801, check horizontal output section. No Variation m Power Supply Output: VR801 (1K),R819 (3K3) R818 (6K8) 0803 (BY159), C806 (10MFd), R821 (1K8), R820 (8K2), D801 (8.lV-zener), Q801 (C1815), R822 (10K) R823 (6K8), D802 (9.1V-zener) C804 (330Ω),R811 (0.22MFd),Q802 (2SA1015) R826A (4K7) Q803 (C1815),R824 (12Ω/1W) R815 (27Ω), C808 (0.lMFd) D803A.D804 (BY159), C807 (100MFd) Q804 (BU506AF) & related parts. Only +110V Supply is Missing From SNIPS: Winding between pin no 3-4 of T801 is open or def R610 (1.2Ω/1W). Relay RL1 def. or set is in Standby (check as given in fault of Standby), D602 (BY159), C610A (100MFd/160V) L601, R610B (120V-zener), check +110V supply line for short. Only Low Voltage Supply is missing From SMPS: Winding between pin no 2-4 of T801 is open or def D810 (BY159). C816 (1000MFd/35V) check low voltage supply line for short. Picture (Raster) Shaking Horizontally: Less AC mains, C815 (100MFd/400V), C610A (100MFd/160V), check bridge rectifier circuit, no variation in power supply output voltage or it is low. Set is in standby i.e. No Power-ON: Low voltage supply from SMPS is missing, R832A (270Ω), C943 (3.3MFd), IC102 (L7805), C942A & C942B (22 MFd), X10 (10 MHz), Q910 (BC558B), R973A (IK), Scientech Technologies Pvt. Ltd.
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ST2651 R973 (390Q), D911 (3.6V-zener), no output from pin no 42 of IC01 IC01 (CTV222S) def, R998 (IK) R1003 (2K2) R1004 (2K4), R1001 (10K) Q911A (BC547B), R1002 (100Ω), Q912 (BC547B) R610A (68Ω), C803A (100MFd) D811 (BY159), relay RL1 defective. Reset Problem: Many a times TV comes in Standby after switching it on by mains ‘On / Off’ switch due to falling the Reset voltage to zero. Therefore check Reset voltage & connected components at pin no 33 of IC01 D911 (3.6V-zener) R973 (390Ω) R973A (1K), Q910 (BC558B) R972 (4K7) IC01 (CTV222S-PRC1). Only LB Band is Not Switching: C920 (100pF), R935 (100K) Q904 (BC547) D902 (1N4148), R940 (10K), R939 (47K), Q907 (BC547B),R938 (10K),RA07 (22K) QA02 (BC558B),CA12 (2.2MFd) tuner IC01 (CTV222S-PRC1) defective. Only HB Band is Not Switching: C920 (100pF), R935 (100K), Q904 (BC547), R937 (10K) RA08 (22K), QA03 (BC558B) CA13 (2.2MFd), tuner IC01 (CTV222S-PRC1) defective. Only UHF Band is Not Switching: C921 (100pF) R934 (100K), Q905 (BC547B), R936 (10K), RA05 (22K), QA04 (BC558B), CA14 (10MFd), tuner,IC01 (CTV222S-PRC1) defective. Tuning is not possible: FT+/FT- keys def check key matrix circuit related with pin no 13 to 20 of IC01, no output from pin no 1 of IC01 IC01 (CTV222S-PRC1) def R908 (1K) C905 (100pF), R907 (5K6) C904 (100pF) R906 (1K5) Q901 (2N2222A), R904 (220Ω) R905 (33K) RA02 (12K/2W) DA13 (33V-zener) CA03 (10KpF) CA04 (lMFd/63V), R903 (15K) C902 (0.1MFd) R902 (10K) C952 (0.1MF), R901 (33K), C901 (0.1MFd), tuner def. Auto Search is Not Possible or Indefinite, Auto-Search I.e. in Auto-Search Mode Tuning Does Not Stop When Any Station is Received: AUTO key is def check key matrix circuit related with pin no. 13 to 20 of IC01 check IDENT at pin no. 34 of IC01, R34 (3K), C951 (820pF) C950 (1KpF) R979 (6K8), Q911 (BC547B), D916 (1N4148) R981 (IK) R978 (4K7), C949 (0.1MFd) R977 (4K7) C948 (1MFd), D918 (1N4148) 0917 (6.2V-zener), R976 (10K) Q912A (BC547B) R975 (4K7) C946 (100pF) R996 (1K) check AFT at pin no 9 of IC01, R942 (4K7) C923 (5K6pf-) Q906 (BC547B), R943 (4K7) check AFT circuit at Video IF Stage, also check as given-in above fault, finally replace IC CTV222S. Power Supply Output is less or Excess: Check AC mains, R826 (4.7Ω/10W), D806-D60Q (4x1N4007), C815 (100MFd/400V) RB04-R803 (220K), R616 (3.3Ω/2W), R817 (3611), C610 (1KpF), R805 (3.3Ω/1W), Q804 (BU508AF) R815 (27Ω/2W) C806 (0.1MFd) D603A-D804 (BAT59), C607 (100MFd), R824 (12Ω/1W) Q603 (C1815) Q802 (2SA1015), D803 Scientech Technologies Pvt. Ltd.
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ST2651 (BY159), C806 (10MFd), D802 (9.1V-zener), R823 (6KB), P822 (10K), R821 (1KB), R820 (8K2) D801 (8.1V-zener) R818 (6K8) R819 (3K3), VR801 (1K) Q801 (C1815).T801 (rare) R6106 (120V-zener) check secondary side of T801. No EHT, Power Supply OK: R444 (1Ω/2W) L406,Q404 (BU508D),C463 (390pF) horizontal driver tralo T401,R416 (2K/3W), C416 (270pF), Q402 (C2229),R411 (33Ω) R408 (1KB) L407,C410 (1KBpF),R416A (6K8/2W) R30C (180Ω),DlA (1N4148) C409 (10KpF) C408 (10MFD/50V),C405 (0.003MFd) R406 (150K),R410 (15K),VR4S1 (10K) IC501 (DBL2003/TA7698AP) No EHT, Power Supply Output Drops: Q404 (BU5060) & its mica, C440 (0 0068MFd) C444 (560pF) horizontal deflection coil, C442 (0.47MFd) D406 (BY159) D408 (BY159) C821 (33MFd) check diodes & capacitors related with EHT winding or + 110V supply line for short or leaky, EHT T461. Horizontal Output Tr. O404 (BU508D) Overheats or Blows ‘Off’: Excess output from power supply Q404 (BU508D) & its mica C440 (0.0068MFd), C444 (560pF), horizontal, deflection coil, C442 (0.47MFd) D408-O406 (BY159), C821 (33MFd), EHT T46V over oscillation in horizontal oscillator, check entire horizontal section & power supply section Vertical Line, Sound Normal: Horizontal deflection coil 01 its wire, C442 (0.47MFd), L411 Width Problem (Width Less or Excess): Less or abnormal output from power supply C442 (0.47MFD/400V), L411 R455 (1K), horizontal deflection coil, C440 (00068MFd) C444 (560pF), Q404 (BU508D), D408-D406 (BY159), C821 (33MFd), EHT T461 check entire horizontal section. Bright White Vertical Strip like Ringing at One Side of the Screen: Check R455 (1K/1W) for open Color Patches on the Screen: Strong magnetic field near picture tube, PTC R802, degaussing con, demagnetize the picture tube with the help of an external degaussing coil, picture tube defective. Memory Problem: Check + 5V at pin no 1&6 of IC104 R988 (100Ω). R988A (100Ω), R985 (3K3), R966 (3K3), R987 (10K), IC104 (PCF8582), IC01 (CTV222S-PRC1) No Operation Through Remote Control Handset While Handset is OK & Front Panel Keyboard is Working Normally: +5V supply to Remote Eye (Sensor) is missing. No output from Remote Eye Sensor) or it is defective R984 (47K), R983 (470K), R982 (1K), IC01 (CTV222S-PRC1) defective Scientech Technologies Pvt. Ltd.
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ST2651 No Operation through Front Panel Keyboard While Remote Control Operation Is OK: Any key in the Front Panel Push Button Keyboard is faulty Keypad dusty or rusty, check key matrix circuit related with pin no 13 to 20 of IC01 R947 to R954 (1K x 8), C924 to C930 & C934 (100pF x 8), 0905-0906 (1N4148) check connection between Main Board & Front Panel Push Button Keyboard, crystal X10 (10 MHz) IC01 (CTV222S-PRC1) defective Volume Up/Dn is Not Functioning: VOL+/VOL- key def check key matrix circuit as given in above fault, no output from pin no 2 of IC01 IC CTV222S-PRC1 def R916 (1K) R915 (15K) R914 (470Ω) R913 (8K2), 0901 (1N4148) Q903 (BC547B) R912 (2K2) C907 (10MFd) R908A (68K) R910 (47K), R909 (22OK) R901 (220K), Q902 (BCS47B) C906 (47MFd) R614 (3K) C603A ,(1MF), IC DBL2002/TA7CTOAP (rare). Brightness Up/Dn is Not Functioning: Check MENU & VOL+VOL- keys, check key matrix circuit, no output from pin no 3 of IC01. IC01 (CTV222S-PRC1) del, R917 (IK) C909 (100RF) R916 (IK) C910 (0.01MFd) C911 (10MFd) R919 (39K) R920 (39K), C207 (22MFd), R212 (10K) R214 (1K5) R352 (5K) R209 (36K), IC DBL2003/TA7698AP (rare). Contrast Up/Dn Is Not Functioning: Check MENU & VOL+/VOL- keys, check key matrix circuit, no output from pin no 5 of ICOI IC CTV222S-PRC1 def R921 (1K3, C913 (100pF) R922 (100K) C915 (0.1MFd) IC103 (LM358N) & its supply, R923-R924 (100K) R925 (10K) R926 (1K), C919 (10MFd) R213 (68K), IC DBL2003/TA7696AP (rare). Colour Up/Dn is Not Functioning: Check MENU & VOL+/VOL- keys, check key matrix circuit, no output from pin no 4 of IC01, IC01 (CTV222S-PRCf) del R927 (1K) C942 (100pF) R928 (100K), C914 (0.1MFd) IC103 (LM358N) & its supply, R931-R929 (100K) R930 (10K) R932 (IK), C916 (10MFd) C506 (10KpF), R505 (27K), IC DBL2003/TA7698AP (rare)
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ST2651 EHT & Sound OK, No Light or Low Light or Dark Picture or Brightness Problem: Adjust screen control, check CRT filament supply, R920 (1.8Ω), C901 (2K2pF). check + 12V supply R448 (6.2Ω) D408 (BY159), C449A (1000MFd), L410, C446 (1000MF), C527 (10MF) C523 (47KpF) check Bright A Contrast control circuits at System Control section R203 (1K5), W201 R210 (1K5) C204 (0.47MF), R209 (36K) R212 (10K) R214 (1K5) R352 (5K) D241 (1N4148), D1 (BY159), D504 (1N4148), R241 (100K), C240 (2.2MFd) D242 (1N4007) R441 (1K) C445 (0.022MFD), R270 (100Ω) D244 (1N4148) R217 (330Ω) D243 (1N60), R242 (56Ω) R219 (220Ω) Q202 (A1015) check pin no 1 2 3 4 23 39 40, 41 and 42 of IC501 IC501 (DBL2003/TA7898AP) def CRT base loose or faulty, check CRT earthling, CRT del. Retrace (White) Lines, Sound Normal: Adjust screen control D406 (BY159), C447 (10MFd), Q202 (AT 015) & related parts IC DBL2003/TA7898AP A related parts, CRT base loose/faulty CRT defective. Retrace Lines With Picture In Full Screen or Only at Top Portion. Sound Normal. Screen control mistimed, R321 (1K) D310 (8.2V-zener) R326 (10K), D202-D203D204 (1N4148), R217 (330Ω), Q202 (2SA1015) & related parts, also check as given in above fault. Raster & Sound OK, No Picture or Weak Picture or Poor Contrast/Contrast Problem: L105, R201 (330Ω) L201 & 2201 C210 (68pF), R204 (820Ω), C202 (150pF), R207 (330Ω), W201 R203 (1K5), R210 (1K5), C204 (0.47MF), R209 (36K) C445 (0.022MF) R441 (1K), C240 (2.2MF), D242 (1N4007) R241 (100K), D504 (1N4148) R240 (100K) check Contrast & Brightness Control circuits at System Control section. Q202 (2SA1015) & related parts check pin no 1, 2 3 4 23, 39 40 41 & 42 of IC501 IC DBL2003/TA7698AP def, check Video IF & AGC. Total Sync Loss, Sound Normal: R301 (750Ω), R302 (560K), C301 (1MFd) D301 (1N4148), C302 (0.01MFd) R307 (56K) C3O3 (560pF), R303 (2M2), IC DBL2003/TA7698AP Horizontal Rolling, Sound Normal: Adjust & check VR451 (10K) R410 (15K), R406 (150K) C405 (0.003MFd), R405 (36K) R404 (3K3), C407 (1MFd), C406 (1MFd), C403 (5K6pF) R403 (3K3), C402 (0.47MFd), R402 (27K) R401 C401 (10KpF) ICDBL2003/TA7698AP. Vertical Rolling, Sound Normal: Adjust & check R351 (220K) R34A (220K), R308 (39K), C306 (0.22MFd) R330 (3K) C321 (0.033MFd) R305 (2K4) C305 (0.015MFd) R310 (10M) C310 (47MFd). IC DBL2003/TA7698AP.
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ST2651 No Colour or Abnormal Colour, Black & White Picture & Sound Normal: Antenna and its wire, balun/adapter, adjust the fine tuning R501 (820Ω), C501 (l5pF) L502,C502 (10pF), R504 (330K), C504 (1MFd) R505 (27K),C506 (10KpF) check Colour Control circuit at System Control section R509 (1K5) R506 (390Ω),C910 (10KpF) R551 (1K), C507 (10KpF), C508 (15pF),L502,chroma delay line X502,L551, R510 (470Ω),C509 (10KpF), C511 (10KpF),C513 (10KpF), C512 (120pF) L552 C514 (047MFd), R515 (820Ω), C515 (22pF), C516 (22pF) R516 (300Q), X501 (443 MHz) R514 (510Ω),L503 C517 (820pF) R517 (82K) C518 (4,7MFd) R520 (1K2), R518-R519 (22K), R552 (5K) C519-C520 (0.022MFd) C319 (0.47MFd) R319 (2K7) D311 (BY159) R322 (1K), R329 (1K), R512 (100K),C524 (22pF), R513 (15K),IC DBL2003/TA7698AP. No On-Screen-Display, Functions are OK: L901, C937-C938 (27pF), C936 (0.1MF), R968 (22K), D907 (1N4148), C934 (100pF), R987 (5K6), R9S6 (1K), R971 (8K2) D906 (9.1V-zener) C935 (100pF) R970 (3K3),R969 (1K), no output from pin no. 22.23 24 & 25 of IC01, IC01 (CTV222S-PRC1) def. check circuits related with pin no, 22, 23 24 & 25 of IC01. Only Red Colour OSD is missing: No output from pin no. 22 of IC01 IC CTV222S def R955 (1K), C931A (100pF).R2 (1000Ω).R3 (390Ω).T2 (C1815), R4 (220Ω) 4 related parts Only Green Colour OSD is missing: No output from pin no 23 of IC01 IC CTV222S def R956 (1K), C931B (100pF), R5 (100Ω), R6 (270Ω).T1 (C1815).R6 (220Ω) 4 related parts. Only Blue Colour OSD is missing: No output from pin no 24 of IC01, IC CTV222S def R957 (1K) C831 (100pF) R8 (100Ω) R9 (390Ω), T3 (C1815), R7 (220Ω) A related parts. On-Screen-Display Blanking Problem: No output from pin no 25 of IC01, IC01 (CTV222S-PRC1) def, R958 (1K), R999 (4K7), Q908 (BC547B), R960-R961 (680Ω).R956 (10K).C832 (100pF).Q909 (BC558B), R965 (330Ω) C933 (220pF).R963 (1K) R964 (330Ω), D910 (1N4148), Q202 (2SA1015) & related parts. No Audio, Picture OK: R601 (6.2Ω), C602 (470MFd), speaker or its wire C601 (470MFd), C608A (47MFd), IC601 (TDA2611) Q801 (A1015) & related parts, check circuit between pin no. 7 of IC601 & pin no 3 of IC101. No Sound, Audio & Picture OK: C602 (68pF), Z601 (5.5 MHz), R602 (2K2),C6.3 (10KpF), L651/ R603, (10K), C617 (68pF), IC101 (TA7680AP), check circuit between pin no. 3 of IC101 & pin no. 7 of IC801, Q601 (A1015) & related parts IC601 (TDA2611) and related parts.
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ST2651 No Picture, No Sound, No Snow, Raster OK: L106.C107 (100MFd),CA08 (220MFd),Q161 (C388A) & related pads, SAW-Filter Z101,L102.R101 (820Ω),C101 (10KpF),C102 (1KpF), R108 (3K9).L151,L105, check AGC,C601 (0.22MFd),R107 (820K),R151 (5K),R105 (330Ω),IC101 (DBL2002/TA7680AP), tuner defective. No Picture, No Sound, Only Snow or Picture With Snow: Antenna & its wire, ballun/adaptor, adjust fine tuning, check Band Switching & Tuning Voltage circuits, +12V to tuner MB is missing.L161,R161 (100Ω),C161 (10KpF);R162 (1K),R163 (5K6),R164 (220Ω).C162 (10KpF).L162,R165 (470Ω), R166 (33Ω),Q161 (C388A),C163 (10KpF),Z101,L102,R101 (820Ω),C101 (10KpF),C102 (1KpF),L151,C601 (0.22MFd),R107 (820K),R151 (5K),C103-C104 (10KpF),R105 (330Ω),R104 (68K).R106 (100K),CA09-CA10 (4.7MFd),IC DBL2003/TA7680AP, tuner defective. Tuning Drifts Automatically/AFT Problem: L152,C174 (15pF),C175-C176 (2.2pF),C172 (1KpF),IC DBL2002/TA7680AP,C178 (1KpF),R171 (1K2),C171 (10KpF),R1 (100K),R2 (56K),R3 (47K),tuner. Horizontal Line, Sound Normal: R327 (10Ω),D302 (BY159),C311 (470MFd),R355(27Ω),R356 (24Ω), C313 (47MFd), R317-R316 (680Ω) C312 (10MFd), Q306 (C2073), Q307 (A940), R325 (330Ω),Q303(C2229),D303 (5.6V-zener),R332 (4.7Ω), R333 (1Ω), D304 (1N4148); C316 (470MFd), vertical def coil & its wire, R323 (1.8Ω), C317 (4.7MFd), C318 (3K3pF), R312 (24K), R313 (15K), R314 (20K), R316 (9K) R30 (3K3), R255 (50K), R311 (24K), C308 (2.2MFd), 0312 (5V-zener), R320 (1K), C306 (0.22MFd), R308 (39K), R34A (220K), & 351 (220K), IC DBL2003/TA7698AP. Height Less or Cinemascope Picture &/or Vertical Non Linearity &/or Vertical Fold-Over Problem, Sound Normal: Adjust & check R255 (50K), less or abnormal supply to vertical section, R327 (10Ω), D302 (BY159), C311 (470MFd), R355 (27Ω), R356 (24Ω), C313 (47MFd), R317R318 (680Ω), C312 (10MFd), Q306 (C2073) Q307 {A940), R325 (330Ω), Q303 (C2229), D303 (5.6V-zener), R332 (4.7Ω), R333 (1Ω), D304 (1N4148), C316 (470MFd), R323 (1.8Ω), (4.7MFd), C318 (3K3pF), R312 (24K), R314 (20K), R316 (9K), R30 (3K3), R311 (24K), C308 (2.2MFd), D312 (5V-zener), R320 (1K), C306 (0.22MFd), R308 (39K), R34A (220K), R351 (220K) IC DBL2003/ TA7698AP, vertical deflection coil. Only Red Colour With Retrace Lines, Sound OK: CRT red cathode voltage will decrease. R591 (15K/2W), Q507 (C2229) & related parts, VR257 (10K), fault In circuit between pin no 21 of IC501 & CRT red cathode, IC DBL2003/TA7898AP, CRT red cathode def, CRT base.
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ST2651 Only Green Colour with Retrace Lines, Sound Normal: CRT green cathode voltage will decrease R902/ (15K), Q508 (C2229) & related parts, VR258 (10K), VR253 (200Ω), fault in circuit between pin no 20 of IC501 & CRT green cathode, IC DBL2003/TA7698AP, X^RT green cathode def, CRT base. Only Blue Colour With Retrace Lines, Sound OK: CRT blue cathode voltage will decrease R593 (15K), Q509 (C2229) & related parts, VR259 (10K), VR252 (200Ω), fault in circuit between pin no 22 of IC501 & CRT blue cathode, IC DBL2003/TA7698AP, CRT blue cathode def, CRT base. Only Secondary Colour Cyan (Red Colour Missing), Sound Normal: CRT red cathode voltage will increase. R901 (4K7), Q507 (P2229), VR257 (10K), C531 (1KpF), R540 (150Ω), R265 (120Ω), C534 (180pF), R527 (560Ω).D502 (1N4148), R522 (2K7), fault in circuit between pin no. 21 of IC501 & CRT red cathode, IC DBL2003/TA7698, CRT red cathode def, CRT base. Only Secondary Colour Magenta (Green Colour Missing), Sound Normal: CRT green cathode voltage will increase. R902 (4K7), Q508 (C2229), VR258 (10K), C543 (1KpF); C582 (1KpF), R541 (150Ω), VR253 (200Ω) R525 (560Ω), D501 (1N4148), R524 (2K7) Fault in circuit between IC501 pin no 20 & CRT green cathode, CRT green cathode def, IC DBL2003/TA7698, CRT base. Only Secondary Colour Yellow (Blue Colour Missing), Sound Normal: CRT blue cathode voltage will increase.R903 (4K7), Q509 (C2229) VR259 (10K). C533 (1KpF), R542 (1503), VR252 (200Ω) C536 (180pF), R526 (560Ω), D503 (1N4148), R522A (2K7), fault in circuit between pin no 22 of IC501 & CRT blue cathode, IC DBL2003/TA7698, CRT blue cathode def, CRT base. Less & /or Distorted Sound, Picture OK: Less or abnormal supply to Sound Section, R601 (6.2Ω), C602 (470MFd), speaker paper cone torn or hard, C601 (470MFd), R602A (6.2Ω), C607 (0.1MFd), C608A (47MFd), IC601 (TOA2611), C605 (0.1MFd), C606 (2K2pF), R605A (56K), R102B (2K2), Q601 (A1015), R622 (2K2), R624 (39K), R623 (1K5), R102A ?2K2), RS1 (10K), CS1 (6800pF), C608 (10MFd), R618 (160K), R617 (4K7), C618 (22MFd), C108 (2K2pF), L651, R603 (10K), C617 (68pF), R602 (2K2), 2601 (5.5 MHz), C602 (68pF), IC101 (TA7680AP) curriculum.
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ST2651 Present Layout Diagram
Figure 30
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ST2651 Actual Shorting Shunt Position of Jumpers
Figure 31
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ST2651 Glossary ACC: Automatic colour control. Aperture Mask: A metal plate with framed holes, placed closely behind the phosphor dot coated screen in a colour T.V. picture tube. Its function is to ensure that each of the three electron beams strikes only the desired colour phosphor dot associated with the beam. This is also known as shadow beam. Aspect Ratio: Ratio of the width to height of picture frame. Active Lines: The television image lines actually visible on screen of picture are 625. Out of these 585 are active, the remaining occur during the vertical retrace period, when the viewing tube is blanked out. Aquadag Coating: It is the conductive graphite coating on inside glass wall of the picture tube funnel or bell, that extends from face plate or screen to about halfway into the narrow neck. This coating acts as final anode. AFT: Automatic fine tuning - an arrangement used in colour T.V. receivers to automatically check and correct the frequency of the local oscillator in the tuner. This ensures that the video IF remains at the correct value and eliminates the need of frequent adjustment of the manual fine tuning control. AGC: A circuit arrangement, which adjusts the gain of the receiver and keeps the output relatively constant, in spite of variation in strength of input at aerial. Balun: An impedance matching device for antennas used between transmissions. Bar Generator: A generator for producing pulses equally separated in time that are synchronized so they produce a stationary bar pattern on a television screen for test purpose. Blanking: The process of applying negative voltage to the control grid of CRT to cut off the electron beam during the retrace or fly back period. Boost Supply: A high voltage D.C. supply produced in a horizontal output section. This boosted +B supply voltage is commonly used for horizontal output tube, vertical oscillator and first anode of picture tube. Blooming: Increase in picture size due to over sweeping because of reduced high voltage to final anode of CRT. Beam: The stream of electrons passing from the cathode to the fluorescent screen of a cathode ray tube. Burst Gate: 8 to 10 cycles of the sub carrier are transmitted in the back porch of the horizontal sync signals. The signals are used for synchronizing the regenerated sub carrier and for obtaining the identifying signal for phase reversed V lines as well to separate these signals a part of the CVD signal is given to the burst gate. The burst gate which is controlled by the line sync pulses allows the signal to pass only during the burst period. Thus it separates the burst signal.
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ST2651 Corona: A point at high potential can ionize the surroundings air to produce a visible corona effect, which is light blue in colour. This causes loss to power. Cascode Amplifier: An amplifier circuit using twin triode tube to provide better gain and less noise. Clamping: Keeping one amplitude at constant level, e.g. the blanking level can be clamped at grid cut off voltage for picture tube. The clamping function is really the same as DC insertion or DC restoration. Chrominance: A colour term defining the hue and saturation of a colour. Chrominance Signal: The U and V sidebands of the modulated colour sub - carrier. These carry information pertaining to the hue and saturation of the colour but no information regarding the brightness. Choke Coil: It limits the flow of alternating current while allowing direct current to pass. Colour Burst: A synchronizing signal consisting of about 10 cycles of colour subcarrier oscillator in the transmitter. It is transmitted during the back porch of the line sync signals and is used to synchronize the colour sub carrier oscillator in the colour TV receiver. Colour Edging: Extraneous colours appearing at the edges of coloured objects and differing from the true colours in the object. CCVS: Composite colour video signal or composite video signal in colour TV receivers. This includes the luminance signals, coded chroma signals, sync signals and the colour sub carrier burst. . Complementary Colour: A colour formed by subtracting a sample colour from white light. For example if red is subtracted leaving green and blue the complementary colour is cyan. Convergence: The cross over of the three electron beams of the three gun tricolour picture tube. This occurs at the plane of the aperture mask. Chroma Delay Line Decoder: The U & V signals are transmitted on a single sub carrier. This is known as quadrature modulation. The function of chroma delay line decoder is to separate the modulated U & V components from the quadrate modulated signals. This decoder utilizes a chroma delay line for separating U & V component. It also electronically averages the U & V component of successive lines thus removing phase distortion, which may take place on long transmission path, Colour Killer: Colour killer is used to block the chroma amplifier on black and white transmission. This is controlled by the colour burst signal and on black and white transmission, when the colour burst is absent it biases the chroma amplifier cut off. Thus it prevents any spurious signals getting through the chroma section which can cause coloured snow on the picture tube screen.
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ST2651 Delay Line: A time delay device consisting of an actual or artificial transmission line, its purpose in colour TV receivers is to ensure the coincidence of the luminance(Y) and the chrominance (U and V) signals. Deflection Yoke: An assembly of one or more electromagnets to produce deflections from one or more electron beams. Detection: Stage in which demodulation or detection takes place. Dropping Resistance: A resistor used to decrease the voltage in a circuit. Damper Diode: Damper diode conducts immediately after horizontal retrace to damp the oscillation in horizontal scanning current, which would otherwise produce thin white vertical lines in raster. Also damper action produces boost supply for anode of horizontal amplifier tube. Finally the damper current provides horizontal scanning for the left side of raster that is why damper diode is also called efficiency diode. Efficiency Diode: Damper diode is also called efficiency diode, because when it is conducting it provides horizontal scanning from extreme left to one third of the length. Equalising Pulses: In television signals the two pulse trains of 6 pulses each which occur just before and just after a vertical synchronizing pulse. Equalizing pulses are short duration pulses. Interval between two adjacent pulses corresponds to horizontal scanning cycle. This is meant to keep horizontal deflection oscillator ready for reversal of direction of current. Fly Back: Retrace, or return time the period during which an electron beam that has concluded one scanning sequence returns to the starting point. Frame: The complete picture or scene to be scanned is called frame it consists of 625 horizontal scanning lines. Gray Scale: In a test pattern a scale that illustrates uniform changes in signal amplitude from white, progressing through Gray values in equal steps to black. Hum: A low audio frequency, having the same frequency as that of the power supply or a harmonic there of introduced, into the signal paths by inductions, leakage or insufficient filtering and heard in the back ground or a received radio programmer or appearing across a television image in the form of one or two horizontal bars. Hue: The dominant wavelength of light representing the colour of an object. It is the redness, blueness or greenness of an object. Hybrid Receiver: In this type, the deflection circuits generally use power tubes, while the signal circuit use transistors and ICs. These receivers usually have filaments connected in series chain. Hold Control: A TV receiver has vertical hold control. The vertical hold control adjust the frequency of the vertical oscillator close enough to 50 Hz so that it is locked by incoming sync pulses. Ignition Interference: Interference produced by auto ignition sparks or other ignition discharges. Scientech Technologies Pvt. Ltd.
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ST2651 Image: A reproduction of a person, object or scene such as that produced by a television receiver. Impregnate: To treat component so as to make it moisture resistance by filling the excess space in its container with a material such as a wax or pitch. Infra Black Region: The portion of the video signal above the black level. It contains the synchronizing pulses. Inter carrier Sound: The RF sound carrier is 5.5 MHz above the picture carrier. All television receivers use 5.5 MHz as frequency of sound IF signal. This 5.5 MHz signal is called the inter carrier sound carrier at 33.4 MHz with picture carrier at 38.4 MHz in video detector. Interlaced Scanning: In television, a system in which even lines of the image are scanned during one downward sweep of the scanning beam and remaining odd frames are scanned during the next downward sweep of the scanning beam. Jitter: Distortion in received television or facsimile picture caused by momentary errors in synchronization between scanner and recorder. Keyed AGC: The AGC circuit employing fly back pulses from horizontal output circuit for keying or gating the AGC rectifier into conduction. The video signal is also coupled into the rectifier to provide AGC voltage proportional to signal strength. However the AGC stage is generally biased to cut off so that it conducts only for the short times when both inputs are present at the same time. Keystone Distortion: A form of distortion in which the television image takes the shape of trapezoid. Because the electron gun is not at right angle to the mosaic this makes the electron path to the top of the picture longer than that to the bottom and consequently the sweep is wider at the top then at the bottom. Lightning Arrester: A protective device used to save building or equipment from lightning. Mast: A vertical pole or structure supporting an antenna. Moire Effect: The effect of poor interlacing is more prominent if the picture has diagonal lines. These diagonal lines appear to be interwoven. This effect is called moire effect or fish tailing. Monochrome Signal: In monochrome television, a signal wave for controlling the luminance values in the picture. Multiband Antenna: An antenna that can be used with satisfactory results on a number of frequency bands. Matrix: Matrix sub section consists of amplifier stages along with voltage combining and dividing networks. This section obtains back the primary colour signals from the chroma signals and the luminance signals given to it. The primary colour signals R, G, B, obtained the matrix section are given to the output video amplifiers circuit. Natural Frequency: In an un damped body or system, the frequency at which oscillation will continue after the applied force has been removed. Scientech Technologies Pvt. Ltd.
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ST2651 Noise Inverter: Also called noise gate, this circuit inverts the polarity of noise pulses by reversing the polarity of its video signal. The purpose is to cancel noise pulses in the video signal to the AGC or sync separator stage. Out of Sync: not synchronized. Television reception in which the lines or frame sweeps or both are not in step with transmitted signal. Overloaded Picture: The picture has reversed black and white values and is out of sync. The picture is out of sync horizontally and vertically because the sync pulses are either compressed or lost completely with the severe amplitude distortion. PAL: “Phase Alteration by Line” - This system is a refinement of the NTSC system and has been adopted in our country. This system was developed in the federal republic of Germany and introduced in 1967. In this system the three colour signals i.e. R, G, B, signals obtained from the colour camera are processed to obtain the luminance signal Y. The luminance and two colour signals are combined to obtained U and V signals. These signals are also quadrate modulated on a colour sub carrier and the side bands are transmitted along with the rest of the video signals. A specialty of this system is that one of the two colours different signals namely V signal is reversed in polarity during alternate lines. Phase Shift: As the quadrate modulation is used for transmitting the chroma signals, the sub carrier used for modulating the U signal has a 90 degree phase shift for demodulating the U signal the phase of the sub carrier given to the U demodulator should also have a 90 degree phase shift. The phase shifter shifts the phase of the sub carrier given to the U demodulator by 90 degree. Purity Coil: An electromagnetic device placed about the neck of a three gun tri colour picture tube. Its function is to control the angle at which the three beams approach the aperture mask. Its correct adjustment produces the pure colours of red, green, and blue on the screen. Purity Magnates: Two magnetized discs placed on the neck of the picture tube. Their correct location helps in getting colour purity on the screen. Peaking Coil: A small coil placed in an amplifying circuit to increase response at certain frequencies, specifically as resonated peaking coils' used in a video amplifier for high frequency compensation in most cases has resistor connected across. Pencil Beam: Emission, from an antenna having the form of narrow conical beam. Picture Element: In a television system, the smallest portion of a picture or scene that is individually converted into an electrical signal. Pedestal: The signal introduced into the complex video signal at or above the black level used to blank out video signals during retrace period. Pincushion Distortion: If deflection is not uniform at the edges of raster, compared with the centre. The raster will not have straight edges, and if the scanning lines are bowed inwards this fault is called pincushion distortion.
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ST2651 Quadrature Modulation: A system for modulating two signals simultaneously on a single carrier enabling simultaneous transmission of two signals. This method is used in the NTSC and PAL colour TV system for transmitting the two colour difference signal. For this the colour sub carriers split in two parts which differ by 90 degrees. One of these modulated by the U signal and the other by V signal. The two are then combined providing the quadrate modulated chroma signal. Raster: The illuminated rectangular area scanned by the electron beam in a picture tube visible when the brightness control is turned up with no signals. Ratio Detector: An FM detector that uses a pair of diodes connected in such a manner that the audio output is proportional to the ratio of the FM voltage applied to the two diodes. Reverse Age: In this method, the transistor gain is decreased by reducing the forward bias at the base toward cut off. Resonance: In a circuit containing both inductance and capacitance a condition in which the inductive reactance is equal to the capacitive reactance. Reference Black Level: The picture signal level corresponding to specified maximum limits for peaks. Ripple: AC component present in DC power supply. Saturation: Degree to which a colour is pure undiluted with white light. A fully saturated colour does not have any white in it. Synchronous Demodulation: In a colour TV receiver the process of separately detecting the U and V side bands of the chroma signal. This requires the colour sub carrier along with the balanced demodulator. Sync Separator: Composite colour signal (CCS)\available from video buffer in chroma section is given to the sync separator. It separates the composite sync from the CCS signal. The horizontal sync signal is obtained from composite sync by differentiator. The vertical sync is obtained from composite sync signal by integration. Screen Grid: A grid placed between the control grid and the anode and usually maintained at affixed positive potential. Second Anode: The electrode in a cathode ray tube that is maintained at a constant positive potential and used to accelerate electron beam. Serrated Pulses: A series of equally spaced with in pulse signal. For example, the vertical sync pulse is serrated in order to keep the horizontal sweep circuit in step during the vertical sync pulse interval. Snow: Effect of random noise on the reproduced picture. It has the appearance of grainy, speckled pattern superimposed on the picture. Solid State Devices: Also called semiconductor devices. These includes diodes, transistor, and integrate circuits. The semiconductor elements germanium and silicon are generally used. Scientech Technologies Pvt. Ltd.
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ST2651 Sound Bar: The audio signal associated with video produces wide horizontal bars in the picture that move in step with the audio modulation and disappear when there is no Voice or music. Sound Take off: At the output of the video in a TV receiver, a 5.5 MHz wave trap is a sound take off circuit. This resonant tuned circuit filters out the 5.5 MHz sound IF signal from video frequencies. Spark Gap Capacitor: These combine the function of a bypass capacitor and spark gap. These are generally used at the electrode of the picture tube. The purpose of the spark gap is to bypass any spark produced in the picture tube to prevent the damage to the transistor amplifiers by the voltage surges. Staggered Tuning: Tuning of inter state coupling circuit of a video IF amplifier to different frequencies with in a desired pass band. Staggered tuning is used to give broadband response. Sub Carrier Generator: As the chroma signals are transmitted after suppressing the carrier, reintroduction of the sub carrier is necessary for demodulating these signals Moreover to obtain the correct colour the regenerated carrier should have the same frequency and phase as that of the sub carrier at the transmitter. The sub carrier generator consists of the sub carrier oscillator and discriminator. The sub carrier oscillator, which is crystal controlled for high stability, produced oscillation at the desired frequency. As even a crystal controlled oscillator cannot ensure the desired degree of accuracy and correct phase of the sub carrier, phase discriminator circuit is used to compare the frequency of the oscillator with the sub carrier burst and to synchronize the phase and .frequency of the oscillation with that of these burst. Sync Clipper: In television, a vacuum tube or transistor circuit that is biased so as to remove the sync signals from the composite video signal. Tearing: An undesirable effect in a received television picture in which groups of lines are displaced, giving the appearance of a tom picture caused by unstable horizontal synchronization. Test Pattern: In order to adjust a television system and compare performance, a standard picture in the form of a test pattern is transmitted. U Signal: A part of the chroma signal in the PAL system. It is derived from the. B - Y signal U = .493 (B - Y). Undamped Oscillation: Oscillation of a electromagnetic wave whose energy source contently restores losses incurred by the load or resulting from radiation. U & V Modulators: The U & V signals from the decoder are modulated signals with no carrier. Carrier of correct phase and frequency is required for demodulating these signals. The U & V demodulators consist of balanced demodulators. These demodulate the modulate U & V signal with the help of reference sub carrier given to
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ST2651 them by PAL switch phase shift and sub carrier generator section. The demodulated U & V signals obtained from the demodulators are given to the matrix section. Video Buffer Amplifier: The CVD signal obtained from VIF section is given to video buffer amplifier which amplifies this signal which consist of luminance signal Y, CHROMA signal R- Y horizontal sync signal, vertical sync signal and the colour sub carrier burst signal. V-Signal: A part of the chroma signal in the PAL system. It is derived from the R - Y signal V = .877 (R - Y). Variac: A transformer whose output voltage can be varied over a wide range by means of a switch and a series of taps. Vertical Blacking Pulses: In television, a pulse transmitted at the end of each field to cut off the cathode ray beam of CRT while it is returning to start of next field, i.e. during vertical retrace. Vertical Hold Control: The control is a television receiver that adjusts the frequency of the vertical sweep oscillator. Vertical Linearity Control: In television control provided for adjustment of the uniformity of distribution of picture elements in a vertical direction. Very High Frequency: A frequency in the band width of 30 MHz and 300 MHz. Videocon: A camera tube in which a charge density pattern is formed by photoconduction and stored on that surface of the photo conductor which is scanned by an electron beam, usually of low velocity electron. Wave trap: It is a series or parallel LC tuned circuit to attenuate a specific frequency. Width Control: The control on a television receiver where the horizontal dimension of the picture is adjusted to fill the picture tube. Y Signal: The luminance part of the colour signals .It contains the information about the brightness part of the picture but no colour information. By itself it can reproduce the black and white picture. This signal is normally derived from the R 0 and B colour signals. Y=0.30% + 0.59% + 0.11%.
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ST2651 Warranty 1.
We guarantee this product against all manufacturing defects for 24 months from the date of sale by us or through our dealers. Consumables like dry cell etc. are not covered under warranty.
2.
The guarantee will become void, if a)
The product is not operated as per the instruction given in the Learning Material
b)
The agreed payment terms and other conditions of sale are not followed.
c)
The customer resells the instrument to another party.
d)
Any attempt is made to service and modify the instrument.
3.
The non-working of the product is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type, serial number of the product and date of purchase etc.
4.
The repair work will be carried out, provided the product is dispatched securely packed and insured. The transportation charges shall be borne by the customer.
List of Accessories Quantity •
Remote ............................................................................................................. 1
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Ballun .............................................................................................................. 1
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11 pin male octal Connector to 11 Pin Male Octal Connector ........................... 1
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8 Pin Male Octal Connector to 8 Pin Male Octal Connector.............................. 1
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26 Pin to 26 Pin Flat Cable Connector .............................................................. 1
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Jumper Pins .................................................................................................... 10
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Trainer Key ...................................................................................................... 1
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Pencil Cell ....................................................................................................... 2
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Mains Cord....................................................................................................... 1
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Learning Material (CD) .................................................................................... 1
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