You have visited the “Teleworkshop” website, its main focus is assistance in repairing electronic equipment for beginning radio amateurs, as well as for those who are interested in electronics and are only taking their first steps in this direction.
However, it will also be useful for more “advanced” repair technicians, since modern electronics are quite complex and often even a good specialist spends a lot of time diagnosing a malfunction, and the site will help remind you of the main malfunctions of TVs or suggest ways to solve new ones.
For beginning radio amateurs, the site has special sections “Understanding the world of electronics”, “Beginner radio amateur” with published materials with which you need to start getting acquainted with the fascinating world of electronics, these are radio components and their design, spare parts for repairs, and where you can get them. There are also materials on the tools necessary for repairs (soldering irons, solder, etc.) In the “Device” section you can find information on the instruments (oscilloscopes, millimeters) necessary for diagnosing faults in household radio electronic equipment.
The quality of the image directly depends on the quality of the received signal, so the topic of an antenna for a TV that receives both analog and digital signals is necessarily touched upon. The design of antennas, what they are, which are better.
With the advent of digital technology, video tape recorders very quickly became a thing of the past, so repair of DVD players and stereo systems will be considered. 
The topic of automotive electronics repair will be touched upon, since there are also plenty of problems in this area. Car radios - cassette, disk, receivers, multimedia, they also break down. In addition, it is possible to modify old but serviceable tape recorders and with such an upgrade, we extend the life of automotive radio electronics.
Let's not ignore new products in the field of television, although it is quite difficult to keep track of them, everything changes so quickly in this area. Since new TVs open up new opportunities, articles will be published on topics related to digital television (cable, satellite, digital terrestrial television DVB-T2).
If you decide to repair your TV yourself, be it Samsung, Philips, LG or Sony, remember that the intervention of an untrained person can aggravate the existing problem and make repairs impossible or unprofitable. If you do not have basic knowledge, and you have problems with equipment, it is better to contact a qualified specialist.
| To view digital TV must be purchaseddigital television receiver. It can be called differently - decoder, receiver Read | 3D LED - LG 32LA643V TV of the 2013 model range, with a diagonal of 32 inches (81 cm), an inexpensive good TV Smart TV. Quite |
It is certainly possible to repair the TV yourself, without resorting to the services of a television technician. What does this require? Basic technical literacy, ability to hold a soldering iron and the ability to carry out basic measurements with a simple tester. A large amount of information about typical defects that the Internet is replete with can encourage even a doubter to start restoring a broken device. Self-confidence is a wonderful quality, but the likelihood of ending up with a completely “killed” device is quite high. Maybe after all?
So, let's start disassembling. Remove the cover from the TV if it is secured with screws or self-tapping screws. Modern TV models, in addition to fasteners, also have a cunning system of latches, which can be quite difficult to open without breaking them or scratching the case. The craftsmen have experience in opening devices and the necessary devices for this, keeping in mind that the connection of the lid to the body is reminiscent of the device of a modern TV remote control, made entirely with latches.
The power supply is designed to generate stable voltages of a given power, necessary for the correct operation of the remaining components of the television chassis. It can be in standby or operating mode, depending on the command from the motherboard. It is the most vulnerable link to external adverse influences such as power surges, lightning strikes, etc. The TV's power supply must use high-quality components that can ensure its uninterrupted operation over a wide range of input voltages in severe temperature conditions.
The motherboard is the “command center” of the entire device. Provides control, switching, adjustments and settings for the TV as a whole. Executes user commands sent from the remote control and local keyboard. It has a developed architecture of data storage devices in the form of Eeproom, Flash, Nand Flash, SpiFlash, RAM chips connected to a central or graphics processor and signal processing devices via the I2C bus - a serial data bus using two bidirectional communication lines SDA and SCL.
An inverter or LED backlight unit ensures trouble-free operation of light sources in the form of lamps or LEDs to illuminate the liquid crystal matrix. It is controlled by commands from the motherboard to turn on and change the brightness of the backlight. They have a serious protection structure that blocks the system not only in the event of a malfunction of the lamp or LED line, but also in the event of a certain imbalance in their operation. Inverter transformers most often fail when diagnosing malfunctions of this unit.
Currently, among budget TVs, models have begun to appear in which all the blocks presented above are made on one board. The power supply, backlight driver, and motherboard are assembled in one unit. The ability to diagnose such a device is hampered by the lack of free access to electrical circuit diagrams and firmware for it. In this case, we recommend turning to professionals. A TV technician will repair your TV at home or in a workshop at a very inexpensive price by today’s standards, will give a guarantee on the work performed and spare parts, and will save you time and nerves.
When deciding to repair your TV yourself, you should soberly assess your technical and professional skills and ask yourself the question: “Will I be able to fix my TV without harming either it or myself.” After all, no one has yet canceled 220 volts, as well as the electrical safety rules when working with electrical installations. It’s one thing if you permanently destroy the “box” - this is only material loss, loss of health is a more significant thing. Think and decide: “Is the game worth the candle?”
Finding a defect is much more difficult than eliminating it, especially for a novice master. The universal method proposed by the author of the article will allow you to quickly and effectively diagnose a modern TV.
WHERE TO START
When repairing television receivers, there are situations when the TV does not turn on and does not show any signs of life. This makes it much more difficult to localize the defect, especially considering that imported equipment often has to be repaired without schematic diagrams. The technician is faced with the task of identifying the malfunction and eliminating it with the least amount of time and effort. To do this, you need to follow a certain troubleshooting technique.
If a workshop or private master values its reputation, it is necessary to start with cleaning the device. Armed with a soft brush and a vacuum cleaner, you should clean the inner surface of the case, the surface of the kinescope and the board of the television receiver. After thorough cleaning, an external inspection of the board and elements on it is carried out. Sometimes you can immediately determine the location of the malfunction by swollen or ruptured capacitors, by burnt resistors, or by transistors and microcircuits that have burned through. It happens that after cleaning the kinescope from dust, instead of a transparent bulb, we see a milky white inner surface (loss of vacuum).
Much more often, a visual inspection does not reveal external signs of faulty parts. And here the question arises - where to start?
POWER UNIT
It is most advisable to start repairs by checking the functionality of the power supply. To do this, turn off the load (horizon output stage) and connect a 220 V, 60...100 W incandescent lamp instead.
Typically, the horizontal scan supply voltage is 110...150 V, depending on the size of the kinescope. Having looked at the secondary circuits, on the board next to the pulse transformer of the power supply we find a filter capacitor, which most often has a capacity of 47...100 μF and an operating voltage of about 160 V. Next to the filter there is a horizontal scan supply voltage rectifier. After the filter, the voltage is supplied to the output stage through a choke, a limiting resistor or a fuse, and sometimes there is simply a jumper on the board. Having unsoldered this element, we will disconnect the output stage of the power supply from the horizontal scanning stage. We connect an incandescent lamp in parallel to the capacitor - a load simulator.
When turned on for the first time, the key transistor of the power supply may fail due to a malfunction of the wiring elements. To prevent this from happening, it is better to turn on the power supply through another 100...150 W incandescent lamp, used as a fuse and switched on instead of the soldered component. If there are faulty elements in the circuit and the current consumption is large, the lamp will light up and all the voltage across it will drop. In such a situation, it is necessary, first of all, to check the input circuits, the mains rectifier, the filter capacitor and the powerful transistor of the power supply. If, when turned on, the lamp lights up and immediately goes out or begins to glow faintly, then we can assume that the power supply is working, and it is better to make further adjustments without the lamp.
Turn on the power supply and measure the voltage across the load. Look carefully on the board to see if there is a resistor for adjusting the output voltage near the power supply. Usually next to it there is an inscription indicating the voltage value (110...150 V).
If there are no such elements on the board, pay attention to the presence of control points. Sometimes the supply voltage is indicated next to the terminal of the primary winding of the line transformer. If the diagonal of the kinescope is 20…21″, the voltage should be in the range of 110…130 V, and if the kinescope size is 25…29″, the supply voltage range is usually 130…150V.
If the supply voltage is higher than the specified values, it is necessary to check the integrity of the elements of the primary circuit of the power supply and the feedback circuit, which serves to set and stabilize the output voltage. Electrolytic capacitors should also be checked. When dry, their capacity decreases significantly, which leads to incorrect operation of the circuit and an increase in secondary voltages.
For example, in an Akai CT2107D TV, when the electrolytic capacitor C911 (47 µF, 50 V) dries out, the voltage in the secondary circuit can increase to 210 V instead of 115 V.
If the voltages are underestimated, it is necessary to check the secondary circuits for short circuits or large leaks, the integrity of the protective diodes R2K, R2M in the horizontal scan power circuit and the 33 V protective diodes in the vertical scan power circuit.
For example, in the Gold Star CKT 2190 TV, with a faulty horizontal power filter capacitor of 33 μF, 160 V, which has a large leakage current, the output voltage instead of 115 V was about 30 V.
In the Funai TV-2000A MK7 TV, the protective diode R2M was broken, which led to the protection being activated, and the TV did not turn on; in the Funai TV-1400 MK10, a breakdown of the 33 V protective diode in the vertical scan power circuit also led to the protection being triggered.
LINE SCAN
Having dealt with the power supply and making sure that it is working, we restore the connection in the horizontal scan power circuit, having first removed the lamp that was used instead of the load.
To turn on the TV for the first time, it is advisable to install an incandescent lamp used instead of a fuse.
If the horizontal scanning output stage is working properly, the lamp will light up for a few seconds when turned on and go out or glow dimly.
If the lamp flashes when turned on and continues to burn, you need to make sure that the horizontal output transistor is working properly. If the transistor is working and there is no high voltage, make sure there are control pulses at the base of the horizontal output transistor. If there are pulses and all voltages are normal, we can assume that the line transformer is faulty.
Sometimes this is immediately clear from the strong heating of the latter, but it is very difficult to reliably say whether the TDKS is working based on external signs. In order to determine this accurately, you can use the following method. We apply rectangular pulses with a frequency of 1...10 kHz of small amplitude to the collector winding of the transformer (you can use the output of the oscilloscope calibration signal]. We also connect the oscilloscope input there.
With a working transformer, the maximum amplitude of the resulting differentiated pulses should be no less than the amplitude of the original rectangular pulses.
If the TDKS has short-circuited turns, we will see short differentiated pulses with an amplitude two or more times smaller than the original rectangular ones. This method can also determine the malfunction of transformers of network switching power supplies.
The method works without soldering the transformer (naturally, you need to make sure there is no short circuit in the secondary circuits).
Another malfunction of the horizontal scan, in which the power supply does not turn on and the lamp, turned on instead of the fuse, glows brightly - a breakdown of the horizontal deflection coils. This malfunction can be determined by disconnecting the coils. If after this the TV turns on normally, then the deflection system [OS] is probably faulty. To verify this, replace the deflection system with a known good one. In this case, the TV must be turned on for a very short time to avoid burning through the kinescope. Replacing the deflection system is not difficult. It is better to use the OS from a similar kinescope with a diagonal of the same size.
The author had to install a deflection system from a Philips TV with a diagonal of 21″ in the Funai 2000 MKZ TV. After installing the new OS on the TV, it is necessary to adjust the beam convergence using a television signal generator.
FRAME SCAN
If the horizontal scan is working properly, then at least a horizontal stripe should be lit on the screen, and if the vertical scanning is working properly, the full raster should be lit. If there is no raster and a bright horizontal stripe is visible on the screen, you should reduce the brightness of the screen by adjusting the accelerating voltage on the TDKS. This is necessary in order not to burn through the phosphor of the kinescope, and only after this should you look for a fault in the frame scan.
Diagnostics in the vertical scanning unit should begin by checking the power supply of the master oscillator and output stage. Most often, power is taken from the winding of a line transformer. The supply voltage for these stages is 24…28 V. The voltage is supplied through a limiting resistor, which must be checked first. Frequent faults in vertical scanning are breakdown or breakage of the rectifier diode and failure of the vertical scanning chip. Rarely, but still, an interturn short circuit occurs in frame deflection coils.
If you suspect a deflection system, it is better to check it by temporarily connecting a known-good coil. Monitoring should be done with an oscilloscope, observing pulses directly on the frame coils.
CINESCOPE POWER CIRCUIT
It happens that the power supply and scanner are working properly, but the TV screen does not light up. In this case, you need to check the filament voltage, and if it is present, the integrity of the kinescope filament.
In the author’s practice, there were two cases when the filament winding of a line transformer was broken (Sony and Waltham TVs). Don't rush to change the line transformer. To begin with, it should be carefully unsoldered, cleaned of dust and carefully inspected the terminals of the filament winding.
Sometimes the break is located near the terminal under a layer of epoxy resin. Using a hot soldering iron, carefully remove part of the resin and, if a break is found, remove it, after which it is advisable to fill the repair area with epoxy resin.
If the break cannot be found, you can wind the incandescent winding on the core of the same transformer. The number of turns is selected experimentally (usually 3...5 turns, MGTF wire 0.14]. The ends of the winding can be secured with glue or mastic.
RADIO CHANNEL, COLOR BLOCK, VIDEO AMPLIFIER
If the scan is normal, the screen lights up, but there is no image, you can determine the faulty unit by the following signs.
If there is no sound and image, the fault must be looked for in the radio channel (tuner and video processor).
If there is sound and no image, the fault should be looked for in the video amplifier or color block.
If there is an image and no sound, the video processor or low-frequency amplifier is most likely faulty.
After checking the supply voltage of the radio channel, you need to submit video and audio signals through the low-frequency input (you can use a TV signal generator or a regular VCR).
If there is no image or sound, you should use an oscilloscope to trace the passage of the signal from the source from which the signal was supplied to the cathodes of the kinescope or, if the audio channel is faulty, to the speakers and, if necessary, replace the faulty element.
If, after applying a signal to the low-frequency input, image and sound appear, then the fault should be sought in the previous stages.
When checking the video processor, you need to apply an IF signal to the FSS input from the generator or from the tuner output of another TV.
If the image and sound do not appear, use an oscilloscope to check the signal path and, if necessary, change the video processor (when replacing a microcircuit, it is better to immediately solder the socket).
If there is image and sound, then the fault should be looked for in the tuner or in its harness. First of all, you need to check whether the tuner is receiving power.
Check the serviceability of the key transistors through which voltage is supplied to the tuner when switching bands. Monitor whether the base of these transistors receives a signal from the control processor, check the value and range of changes in the setting voltage, which should vary within 0...31 V.
When diagnosing tuner malfunctions, you need to send a signal from the antenna to the mixer, bypassing the RF amplifier stages. To do this, it is convenient to use a probe, which can be made from a disposable syringe with a removed piston. An antenna socket should be installed at the top of the syringe and the central contact should be connected to the needle through a 470 pF capacitor. We bring out the ground using a regular wire; For convenience, it is better to solder an alligator clip to the ground wire. We connect the probe to the antenna plug and supply the signal to the tuner stages.
Using such a probe, it was possible to determine a malfunction in the tuner of the Grundig T55-640 OIRT TV. The first UHF stage in this device was faulty. The problem was resolved by applying the signal through a 10 pF capacitor directly from the antenna jack, bypassing the first transistor, to the next tuner stage. The image quality and sensitivity of the TV after this modification remained quite high and did not even affect the operation of teletext.
CONTROL BLOCK
Particular attention should be paid to diagnosing the TV control unit.
When repairing it, it is advisable to use the diagram or reference data for the control processor. If you cannot find such data, you can try to download it from the website of the manufacturer of these components via the Internet (http://www.bgs.nu/sdw/shtml).
A malfunction in the unit may manifest itself as follows: the TV does not turn on, the TV does not respond to signals from the remote control or control buttons on the front panel, there is no adjustment of volume, brightness, contrast, saturation and other parameters, there is no adjustment to television programs, settings are not saved in memory , no indication of control parameters.
If the TV does not turn on, first of all we check the presence of power to the processor and the operation of the clock generator. Then you need to determine whether the signal from the control processor is sent to the switching circuit. To do this, you need to find out the principle of turning on the TV.
The TV can be turned on using a control signal that triggers the power supply, or by unblocking the passage of horizontal trigger pulses from the master oscillator to the horizontal scan unit.
It should be noted that on the control processor the signal to turn on is designated either Power or Stand-by. If a signal is received from the processor, then the fault should be looked for in the switching circuit, and if there is no signal, you will have to change the processor.
If the TV turns on but does not respond to signals from the remote control, you need to first check the remote control itself. You can check it on another TV of the same model.
To test remote controls, you can make a simple device consisting of a photodiode connected to the CP-50 connector. The device is connected to an oscilloscope, the sensitivity of the oscilloscope is set within 2...5 mV. The remote control should be pointed at the LED from a distance of 1...5 cm. On the oscilloscope screen, if the remote control is working, bursts of pulses will be visible. If there are no pulses, we diagnose the remote control.
We check sequentially the power supply, the condition of the contact tracks and the condition of the contact pads on the control buttons, the presence of pulses at the output of the remote control microcircuit, the serviceability of the transistor or transistors and the serviceability of the emitting LEDs.
Often, after the remote control is dropped, the quartz resonator breaks down. If necessary, we replace the faulty element or restore the contact pads and the coating of the buttons (this can be done by applying graphite, for example with a soft pencil, or by gluing a metallized film to the buttons).
If the remote control is working properly, you need to trace the passage of the signal from the photodetector to the processor. If the signal reaches the processor, but nothing changes at its output, we can assume that the processor is faulty.
If the TV is not controlled from the buttons on the front panel, you must first check the serviceability of the buttons themselves, and then monitor the presence of polling pulses and their supply to the control bus.
If the TV is turned on from the remote control and pulses are sent to the control bus, but the operational adjustments do not work, you need to find out which pin the microprocessor uses to control this or that adjustment (volume, brightness, contrast, saturation). Next, check the adjustment data paths, right down to the actuators.
The microprocessor produces control signals with a linearly varying duty cycle, and when arriving at the actuators, these signals are converted into a linearly varying voltage.
If a signal arrives at the actuator, but the device does not respond to this signal, then this device must be repaired, and if there is no control signal, the control processor must be replaced.
If there is no tuning to television programs, first check the subband selection node. Typically, through buffers implemented on transistors, voltage is supplied from the processor to the tuner pins (0 or 12 V). Most often it is these transistors that fail. But it happens that there are no subband switching signals from the processor. In this case, you need to change the processor.
Next, we check the tuning voltage generation unit. The supply voltage usually comes from the secondary rectifier from the line transformer and is 100...130 V. From this voltage, 30...31 V is formed using a stabilizer.
The microprocessor controls a switch that generates a setting voltage of 0...31 V using a signal with a linearly varying duty cycle, which, after filters, is converted into a linearly varying voltage.
Most often, the 30...33 V stabilizer fails. If the TV does not save settings in memory, it is necessary to check the data exchange between the control processor and the memory chip via the CS, CLK, D1, DO buses for any setting. If there is an exchange, but the parameter values are not stored in memory, replace the memory chip.
If the TV does not have an indication of control parameters, it is necessary in the indication mode to check the presence of packets of video pulses of service information on the control processor along the R, G, B circuits and the brightness signal, as well as the passage of these signals through the buffers to the video amplifiers.
In this article we touched on a small part of the faults that occur in television receivers. But in any case, the method of finding them will help you correctly identify and eliminate the malfunction and will reduce the time spent on repairs.
Every TV repair should begin with a fault analysis. First of all, try to understand what could have caused the breakdown. Which node has failed? Then read the repair instructions suitable for your case, download the service disassembly instructions and the TV diagram. Based on the digested technical information, assess the possibility of repairing it yourself, whether you can carry it out without resorting to the help of service centers.
I present to your attention a special troubleshooting technique for beginners, which will help you feel confident during repairs. The table below provides a description of the most common faults and provides valuable advice on which unit needs to be inspected and repaired.
It is worth remembering that if during repairs you find darkening, carbon deposits, swelling and even rupture of radio elements, then you cannot immediately replace them with new ones. A burnt component in many cases is a sign of a short circuit, and the cause is hidden in a completely different place.
When repairing TVs, you should not rush; if you are at a dead end, then it is better to rest or do something else. During the rest process, a decision may come that will determine further repair actions or suggest a specific malfunction.
Also, when repairing TVs, knowledge is required, because usually malfunctions arise due to the failure of elements such as zener diodes, diodes, transistors, resistors and capacitors, and in order to determine the malfunction of an individual, practical knowledge of checking them is needed.
How to check television radio elements:
If the power supply unit (PSU) does not start, then most likely this was due to a breakdown of the power supply microcircuit or transistor, due to overloads that occurred in other units as a result of swelling of electrolytic capacitors or an increase in their equivalent resistance (esr).
This is a good collection of tips from amateur radio professionals on troubleshooting in the circuits of various televisions, in addition, the recommendations received will be useful to both the radio amateur and the repairman of household appliances.
Suddenly the TV spontaneously began to switch channels as it pleased, and not as we needed. A similar problem can also sometimes be accompanied by the fact that the TV spontaneously goes into auto channel search mode and does not respond to the control panel.
As we know, the best repair is prevention of repairs, so here are some simple tips for the future that will extend the life of your device:
1.Don't let children play with the remote control. They manage to enter service mode and reset all factory settings.
2. After turning on the TV with the “Network” button, you should not issue commands from the remote control earlier than 3...7 s. There is also no need to repeatedly press the “Network” button when the TV’s power plug is turned on. The fact is that after supplying the supply voltage, transient processes occur in the TV, and the submission of commands from the remote control at this moment makes the behavior of the TV control system unpredictable.
3. When repairing a switching power supply domestic or imported TV, you should disconnect its outputs from the TV. In this case, you should load its output, which powers the horizontal scan (usually the rated voltage on it is 105... 150 V), with an incandescent lamp 220 V 60... 100 W. This will make repairing the source more convenient and will protect other components of the TV from voltage surges at its output.
4. Never install a table lamp on the TV cabinet. The lamp may fall and not only break itself, but also break the neck of the TV picture tube. And in this case, expensive repairs will be required.
5. The presence of a large amount of dust inside the TV is caused by the use of high voltages in the TV. As is known, cleanliness is the key to health. Therefore, you should take advantage of the moment and remove dust from the high-voltage wires, TDKS, kinescope board and high-voltage kinescope suction cup. Cleaning can be done either with a blow-out vacuum cleaner or with a soft, slightly damp cloth.
6. During repairs, you should not replace failed electrolytic capacitors with capacitors designed for a much higher voltage. For example, a capacitor rated for 10 V should not be replaced with a capacitor rated for 100 V. When replaced, capacitors lose capacitance over time.
7.Any soldering or repairs to the TV should be carried out only when it is completely disconnected from the power supply. Otherwise, you not only risk electrocution, but you may also introduce additional faults by accidentally shorting adjacent pins while soldering.
8. Printed circuit boards in the TV, especially the kinescope board and the board on which the line scan is placed, sometimes become charred under the influence of high temperatures and voltages. The charred section of the board must be cut out, and the printed conductors running on it must be replaced with overhead wires.
9. In cable television networks, the first frequency channel receives strong interference from radiotelephones using the same frequencies. Shielding and other means are usually useless here. There is only one way out - do not watch this channel.
10. In cable television networks, different channels are transmitted with different signal levels. Due to the lack of selectivity of the TV, you end up seeing on its screen an overlap of two images from adjacent channels. To eliminate this effect, you should reduce the sensitivity of the TV using the trimming resistor “AGC Threshold” (“AGC Delay”).
11. When repairing a TV, you should pay special attention to the absence of installation defects: breakage of printed tracks, their mutual short circuit, “cold” soldering. These defects should be eliminated first.
Malfunctions of power supplies can be reduced to the following.
In this case, as a rule, the mains fuse of the TV fails. Before turning on the TV after replacing this fuse, so as not to make unnecessary repairs later, you should:
Make sure that the mains voltage rectifier and filter capacitor are in good working order and that they are not shorted by a broken power transistor
disconnect the load from all secondary rectifiers of the source (you can simply unsolder the rectifier diodes of all sources except the horizontal scan power supply from the monoboard). It is necessary to check the serviceability of the diodes and capacitors of the secondary rectifiers. Faulty elements - replace
load the horizontal scan power source with a 220 V 40...60 W lighting lamp or 4 PEV-10 91...120 Ohm resistors connected in series. This is necessary in order to avoid power supply failure when idling.
supply the supply voltage, while 220 V must be supplied to the IP input through a series-connected lighting lamp. This lamp will act as a non-linear fuse and protect the source from further damage.
it is better to replace all electrolytic capacitors with a rated voltage of 16... 100 V, installed in the “network” part of the IP, with new ones.
If, when you turn on the IP, the lamp connected to the 220 V power supply lights up brightly, there is a short circuit in its primary circuits or its power transistor is open almost all the time due to a malfunction of the control circuit. In this case, you should check the serviceability of the control IC, zener diode and low-power transistors. Sometimes a powerful resistor, which plays the role of a current sensor in a power transistor, fails.
The TV does not turn on in operating modeIn this case, as a rule, there are voltages at the output of the IP, and the TV does not turn on in operating mode due to failures of the TV control system, the horizontal scan supply voltage switch, or failures that occurred in the TV due to an excessive output voltage of the IP. In this case, during repairs, you should highlight the indicated elements on the TV board and make sure they are in good condition.
The TV may also not turn on due to the operation of protective elements: fuses or a zener diode, which breaks down when the horizontal supply voltage is too high.
Background in the sound channel.This defect manifests itself when the capacity of the filter capacitors of the secondary rectifiers of the power supply decreases due to aging. These capacitors should be replaced with new ones.
TV repair - the horizontal output transistor burns out periodically.This occurs due to a significant excess of the output voltage of the IP. The horizontal scan supply voltage, as a rule, is 105... 140 V. Moreover, higher voltage is typical for TVs with a large screen size - 25 inches. Sometimes the TV board indicates the value of this voltage. Otherwise, it can be judged by the rated voltage of the capacitors installed in this circuit. If a capacitor with a permissible voltage of 150 V is installed, and the operating voltage is 140 V, then it is clearly too high. In a working IP, the output voltage should be regulated by an adjusted resistor within ±3% or more. If this does not happen, there is a malfunction in the IP.
An extremely unpleasant manifestation of this defect is a periodic (once a week or month) increase in the output voltage of the IP due to malfunctions of the elements in its feedback circuit. This could be, for example, a reversible break of a diode from the feedback winding or a periodic failure of an optocoupler. In this case, it is better to immediately replace all suspicious elements with new ones.
Control systemManifestations of a malfunction in the control system are very varied: from the inability to turn on the TV from standby mode to the refusal to work from the video input.
The filament of a kinescope is a special filament that heats the cathode of the kinescope for its further operation. It is located next to the neck of the kinescope, and during normal operation, the neck should glow a little. It is clear that if there is no heat, then you will not see the image.
TV repair - does not turn on in operating mode
The reason may be a malfunction of the control unit, corruption of the program in the EEPROM, or a previous failure in other components of the TV, for example, in the horizontal scan.
The TV does not tune to TV channels
In this case, operation from the AV input may be normal. The reason is usually a malfunction of the PROM, PU, the key that generates the control voltage to the TV tuner, or the APCG system.
The TV does not work in one or more subbands
The reason may be a failure of the tuner, keys switching tuner subbands or control unit.
No sound or incorrect volume adjustment
The reason may be a failure of the control unit, a failure in the EEPROM or in the unit for matching the audio control input of the video processor and the control unit.
To power the control system, a separate voltage stabilizer is used. In addition, in standby mode, the supply voltage can be supplied only to one part of the control unit, and to the other part only when switching to operating mode. Therefore, first of all, you should find power stabilizers and make sure they are working properly.
It accounts for a significant number of TV malfunctions. A feature of horizontal scanning on modern televisions is that it is used as a source of secondary voltages to power the video processor, vertical scanning, UMZCH, etc. In modern TVs, the power supply, as a rule, produces only 2 supply voltages: for operating the TV control system in standby mode and for powering the horizontal scan in operating mode. The remaining voltages are generated by secondary rectifiers and stabilizers connected to a diode-cascade line transformer (TDKS).
In single-board TVs, as a rule, horizontal trigger pulses from the video processor are supplied to an intermediate horizontal scanning stage, which can be powered either from the main horizontal scanning voltage or from another source. From the secondary winding of the interstage transformer, pulses amplified by the intermediate stage are supplied to the base of the horizontal output transistor. This line scan construction is the most reliable. Line scan TVs that do not have an interstage transformer are much more capricious and less reliable. Therefore, if you cannot repair a horizontal scan, in which the output transistor is galvanically connected to two to four other transistors, you can replace these transistors with a standard intermediate amplifier from 3...5 USCT.
High voltage transistor failure, as a rule, is called:
overestimated MS supply voltage supplied from the IP;
its overheating due to improper operation of the TV;
violations in the formation of horizontal scanning pulses in the video processor.
TDKS failure. Very common, since this element of the TV works with the highest voltages, and its reliability is not very high
Frame scan
Frame scanning (FR) does not account for many breakdowns, but they are quite unpleasant:
lack of vertical scan
raster distortion
First of all, you should check whether the supply voltage is supplied to the frame scan, as a rule, from the TDKS TV. If the size or linearity of the raster is violated, you should try to eliminate these defects with variable resistors located next to the IC KR, or change the data in the service menu of the TV. If this does not help, or, moreover, nothing has changed with these manipulations, you should check:
the shape of the pulses arriving at the CD from the video processor;
the presence of ring cracks around the terminals of the IC KR;
serviceability of electrolytic capacitors “piping” IC KR;
serviceability of personnel deflection coils OS.
Video processor and radio channel
These TV components account for a number of very unpleasant TV breakdowns when, for example, the TV works from the AV input, but does not receive TV channels.
The wide variety of video processors and tuners does not allow us to consider each of them separately, but they have a number of common faults:
video processor overheating
cracks in the soldering of the tuner pins to the monoboard and in the soldering inside the tuner itself
loose or broken tuner antenna socket.
You can eliminate overheating of the video processor by attaching a U-shaped plate made of duralumin or copper to it
- The practice of repairing a CRT TV, with a typical fault manifested in the absence of red color in the image. The main cause of such a breakdown can be either a dead kinescope or a burnt-out red video amplifier.
It's no secret that a breakdown of a television receiver can ruin the mood of any owner. The question arises, where to look for a good technician, do you need to take the device to a service center? You need to spend your time on this, and most importantly, money. But, before calling a technician, if you have basic knowledge of electrical engineering and know how to hold a screwdriver and a soldering iron in your hands, then in some cases it is still possible to repair the TV yourself.
Modern LCD TVs have become more compact, and their repair has become much easier. Of course, there are breakdowns that are difficult to detect without special diagnostic equipment. But most often there are faults that can be detected even visually, for example, swollen capacitors. In case of such a breakdown, it is enough to unsolder them and replace them with new ones with the same parameters.
All television receivers are identical in design and consist of a power supply unit (PSU), a motherboard and an LCD backlight module (lamp is used) or LED (LED is used). You shouldn’t repair the motherboard yourself, but the power supply and the screen backlight are quite possible.
When repairing LG, Sharp TVs with an LCD display, Rubin, Horizon with the same screens, a situation often arises when, even though the device is in good working order, it does not turn on. It turns out that the cause may be in the antenna cable. This happens because the noise reduction protection is triggered (in Rubin TVs, they began installing it not so long ago), and the unit goes into standby mode. Therefore, if you find your TV is not working, you should not panic, but you need to check the presence of a signal from the transmitting station.
In conclusion, we can say that when you decide to repair a television receiver yourself, you should soberly assess your abilities and knowledge in this matter. If you don’t feel confident, then it’s better to entrust this matter to a TV technician, especially since no one has canceled 220 V, and ignorance of basic safety rules can lead to unpleasant consequences.
