repair secrets

TV Repair Secrets and Repair Tips

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The troubleshooting procedure for each TV model is individual, to a certain extent, it depends on the experience of the repairman and the equipment of his workplace with measuring instruments. And what about linear radio mechanics, if he only has a tester?
Repair of the TV must begin with a survey of the owner of the TV about the nature of the malfunction, as well as, how did it manifest for the first time. If a, For example, from the owner’s explanation it became clear, that the raster disappeared on the TV, but at the moment of disappearance, a vertical strip appeared briefly, which is currently not observed, then the cause of the defect must begin to be sought in the lowercase scan of the device or its power circuits. It should be understood, that the owner does not always correctly formulate his answers to the questions of the repairman. For most, the term “raster” is not clear, etc.. Therefore, the absence of this same raster is usually described as: "Missing image". In this case, you need to ask again: "The screen is dark?». Only an affirmative answer to this question allows us to conclude that there is no raster. A correctly conducted survey of the owner allows you to quickly find the cause of the defect, and the wrong one can drag out the search. If a- the survey revealed, that the TV is “off, does not smoke or shoot ", then it can be turned on so, to pre-diagnose a malfunction by external signs.
Many defects can be found by an external inspection of the installation of the device. In doing so, look for poorly inserted connectors., треснув­шие, broken and burnt parts, shorting the terminals of adjacent parts and wires, dry soldering, soldered ring cracks, ragged tracks etc.
When repairing TVs, it is convenient to use the installation diagram of the device, special? if a table with the coordinates of the main parts is attached to it. Wiring diagrams are sometimes found in repair instructions. (Service Manuals).
Power Supply Failures
Such malfunctions, as short circuits in the primary circuit of the power supply (BP), resulting in a blown mains fuse and an open in these circuits? radio mechanics do not cause difficulties and omitted to save space. Let's move on to more complex defects..
Mains fuse lit
After replacing the fuse and other, failed parts (rectifier bridge, microchips of a converter or a powerful output transistor, etc.), when you turn on the database can "go into the ranks" due to the unredeemed root cause of this defect. Therefore, the first inclusion after such a repair is desirable to produce, disabling VKSR? soldering the inductor in the power circuit of this cascade and loading the power supply on a lamp with a power of 60 W. In addition, it is necessary to limit the power supply current., turning on a lamp 150 in series with it in the network break…200 W
If at the same time the voltage of the VKSR is overstated, it follows, verify: PWM controller PSU, stabilization circuit (comparison chart). If there is an optocoupler in the feedback circuit of the stabilization circuit for galvanic isolation, then it should be checked by replacement.
TV not included, standby indicator is off
1. BP converter should be considered not working, if all secondary voltages of the power supply are absent with approximately 300 In the output of the network rectifier. This voltage is conveniently measured on the accumulative
filter capacitor or on the corresponding output of a pulse transformer (TPI).
If this voltage is, then the first thing to check is the integrity of the primary winding of the TPI and the elements of the startup circuit.
Check Positive Feedback Circuit.
Check for short circuits of the secondary voltage rectifiers, and first of all - VKSR power circuits.
Check electrolytic capacitors and diodes of secondary power supply rectifiers.
2. Check control processor power supply voltage (in modern TVs there are two values ​​of this voltage: +5 and +3,3 AT). If it is underestimated or absent, then check the appropriate stabilizer, as well as the presence and magnitude of the voltage at its input.
If there is voltage at the input of the voltage regulator of the control processor and there is no voltage at its output, except for the stabilizer, should check, are there any short circuits (KZ) power supply circuits +5 AT (+3,3 AT). This is conveniently done by exclusion., sequentially soldering microcircuit pins, to which it arrives, followed by turning on the device and checking for availability +5 AT (+3,3 AT). Faulty chip should be considered, when the power leads are disconnected, the voltage at the output of the stabilizer is restored. This technique can be used to search for short circuit in other TV circuits..
If voltage +5 AT (+3,3 AT) no short circuit in the supply circuit of this voltage is not detected, and at the input of the stabilizer voltage is normal, then the stabilizer itself should be considered faulty.
No raster and sound
1. TV does not go from standby to working. 1.1. Check for an active level of the POWER command on the corresponding output of the control processor. If this level is not, and it does not appear when trying to transfer the TV from standby to working, then this suggests, that the processor is frozen. There may be several reasons for this defect.: ♦ processor voltage is too high or too low;
processor ripple voltage increased;
missing RESET command ("Reset");
no clock pulses;
one or more buttons of the local keyboard are closed (this defect is typical for matrix-type keyboards, which are not used in televisions, presented in this book);
impaired bus exchange;

the control processor itself is faulty.
Power ripples occur, usually, due to loss of capacity by BP oxide capacitors. The ripple level can increase with an excessive increase in the current consumption of one of the cascades, powered by the same rectifier, as the processor.
At the RESET input of the processor, the normal voltage in the operating mode should be approximately equal to the voltage of the power supply with the active level “log. ABOUT", and about 0 in the active level of "log. 1». Only when the TV is turned on, a reset pulse is formed on this output using external elements (in the first case, negative, and in the second positive). If the voltage levels at the RESET pin do not match or if there is no reset pulse at the time of switching on, check the reset circuit. If it contains an oxide capacitor, then first of all it is necessary to check it. If processor power is normal, reset circuit details OK, and on the RESET pin of the processor, the voltage is not normal, then the processor itself should be considered faulty.
To synchronize the operation of all processor nodes, the pH contains a clock generator with an external quartz resonator. In this case, a characteristic defect is poor-quality soldering of the conclusions of the quartz resonator. Another fixable clock defect, CPU freezing, is a malfunction of the quartz resonator itself, what can be checked by replacement method. If the extreme terminals of the quartz resonator are connected to the housing through capacitors, then these capacitors should also be checked, replacing them with known good service. •
1.2. If the POWER command is issued, and the operating mode does not turn on, key cascades should be checked, enabling this mode.
1.3. If, when a POWER command is issued, the PSU operating mode is briefly turned on, and then the TV goes into standby again, then this indicates a protection circuit is triggered.
2. If, when a POWER command is issued, the operating mode of the PSU, but there is no raster and sound, then you should check
the presence of the voltage of the video processor.
If this pressure is not, then check the video processor power circuits (VP), and if necessary replace it.
If there is a supply voltage, then check the line voltage of the horizontal output stage (VKSR), which is usually indicated on the diagrams + B. If this pressure is not, then you should check the supply circuit of this voltage to the horizontal output stage.
If the power supply voltage of VKSR + V is greatly underestimated (at 1.5…2 fold), then the base and emitter of the VKSR transistor should be shorted. If + B increases to approximately the nominal value,-then this indicates a TDKS malfunction or the presence of short circuits in the circuit * of the secondary windings of this transformer.
If voltage + V is, you should check for the presence of horizontal pulses based on the transformer. Indirectly, this can be done., measuring there constant voltage with a tester. If there is a slight negative voltage on the base of this transistor (approximately 0.4…1 AT), then lowercase start pulses are present there. If at the same time there is no heat of the picture tube and high voltage, it should be checked for breakage of its collector transistor VKSR and TDKS.
If there is no negative voltage at the base of the VKSR transistor, it is necessary to check the supply voltage of the transistor of the end-stage cascade of rows, this transistor and interstage line transformer itself (surprisingly frequent defect), as well as the presence of lowercase trigger pulses from the video processor.
Raster is, no sound or image
Check for interference signal from tuner IF output, touching a screwdriver to this conclusion.
If the signal from the IF tuner output passes, then check the following voltages at the terminals of the tuner: feeding, ARU, tuning and range switching (for SR-375).
If any of these voltages is not correct, it is necessary to check the chains of its formation and supply, as well as the tuner itself for the presence of short circuit. It should be remembered, what voltage settings
and range switching are formed from signals from the control processor, AGC voltage - in the video processor. If the voltage at the terminals of the tuner is normal, and the IF signal from the IF output passes, then the tuner itself should be considered faulty.
If the IF signal from the IF tuner output fails, the TV responds to the signals of the local keyboard and remote control, and signals from AV- entrances pass, then it should be checked by replacing the surfactant filter and video processor.
If the IF signal from the IF tuner output fails, TV does not respond to local keyboard and remote control signals, then check the voltage on the PC bus lines. In standby mode on both lines of this bus about 5 AT, and in the worker a little less. If the voltage on them is greatly underestimated, then you need to check by alternately replacing the chip, PC related (Cm. also n. 1.1. "no raster and sound" malfunctions).
No picture, raster (in some cases a dark raster) and there is sound
Check PCTS at the video processor output; if not, replace this chip.
If there is a PCTS at the output of the video processor, then you should check the RGB signals on the corresponding terminals of the VP chip.
If there are no RGB signals, then you should check this chip by replacement.
If there are RGB signals at the terminals of the VP chip, then check the kinescope board, kinescope glow, the presence and magnitude of accelerating and high voltage, and I am also a kinescope. If circuit solutions allow, check the regulating voltages on the brightness and contrast adjustment buses.
No sound, normal image
Schematic solutions for sound channels are diverse, but in most cases, the passage of the signal through the sound channel can be traced, applying an interference signal to the inputs of the corresponding stages. If circuit solutions allow, you should check the volume control voltage and the MUTE command (muting).
With this malfunction, the voltage of the UMZCH should also be checked. If this voltage is present, check the voltage at the output terminals of this chip. The voltages at these terminals should be equal to half the supply voltage. If the values ​​of these voltages deviate from the norm, the UMZCH chip must be replaced. It is also necessary to check the isolation capacitors.

Other malfunctions
Vertical non-linear distortion that cannot be corrected by adjustment and the lack of vertical scanning most often occurs when the output vertical microcircuit malfunctions.
White Balance Disorders (also not removable by adjustment) may occur when there is a malfunction of the video processor or video output amplifiers.
There can be several reasons for the frequent failure of the transistor of the horizontal output stage: increased supply voltage, dry soldering terminals interstage horizontal transformer (ТМС), loss of capacitance by the capacitor of the power filter of the end-stage cascade of rows, open of correction capacitors, which are connected in parallel with the horizontal output transistor.
In conclusion, I want to draw the reader’s attention to the fact, that the same malfunctions in different devices of even one model can manifest themselves in different ways, which complicates their search

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