Why not showing a TV

Below is a drawing of the inverter. Simplified, but it is easy to understand why the TV is not showing, to eliminate the malfunction. What kind of beast is an inverter, how to handle it? Let's answer the question, learn something new about modern technologies. The topic is close to welders, similar methods are used to ignite the electrode. Plus in adjustability. The pulse width modulator easily changes the operating voltage of the transformer primary winding by varying the current. Increased frequency is used to reduce the size. On ultrasound, the transformer takes up much less space.

inverter switching circuit. Work of a modern

TV. There is sound, there is no picture - breakage concerns imaging circuits. Able to refuse a scan, but in most cases the case is explained as follows. Previously, the beam tube dominated in television, they paid triple attention to the posistor, today LCD monitors cannot do without illumination. Moreover, the quality / price of the device mainly depend on it. Different techniques are used for illumination, usually ordinary halogen lamps covering the perimeter or part. Organic diodes are not affordable for everyone. Lamps for ignition, burning require the creation of discharge. The process of ionization of gases is impossible without high voltage. How to get in a miniature( relatively) device?

The correct answer: a transformer. To get a thousand transformers out of twelve volts, look for a large transformer. .. Therefore, a pulse generator controlled by a pulse width modulator is used. Simply put, key, inverter. Clocked in the circuit cuts the signal, in our case it forms the necessary steepness of impulses to pass the transformer easily. Determined by the width of the pulses, the signal power changes. This is how the current is regulated:

  1. At the initial moment, the output of the circuit is empty, the brightness regulator is de-energized with a broken key. The circuit is ready to start generation.

    TV Repair.

  2. . The key receives a permit voltage of +5 V, the dimmer meets the power. A control signal is generated, which arrives at the pulse-width modulator along the left branch.
  3. A signal of the desired duration begins to be controlled by an inverter that triggers a transformer.
  4. The current passes through the isolating capacitors to the lamps, creating a discharge, setting them on fire.
  5. In the feedback circuit, the current reaches the pulse-width modulator along the right branch.

The question arises: why do we need an inverter, if the pulse-width modulator could control the transformer itself? It is associated with load capacity. Chip detects a certain power dissipation limit. The series of microcircuits are trying to hide in the same case, achieving the same type. It is permissible to combine the inverter and the pulse-width modulator in one circuit, they do not often, the current consumption of the assembly will increase. Consequently, the power dissipation will increase. Will lead to a violation of uniformity.

Inverter is a simple circuit, often on one key element. Therefore, using it is easy to obtain a significant output current without losing uniformity. The resolution key is usually generated by semiconductor transistors. The power reaches the dimmer, the voltage level of which controls the pulse width modulator. More pulse width, brighter image. The incoming signal by the lower branch( see figure) repeats the shape, controlling the winding of the transformer. The secondary circuit generates a current. Illumination lamps are lit.

Feedback current circuit

The feedback current is compared with the dimmer signal of a comparator that is part of a pulse-width modulator. At a mismatch the duration of impulses is regulated in the necessary side. That's the whole inverter. Familiar to welders, converts DC to AC voltage by controlling signal parameters. Voltage rises, welders need a significant arc current.

TV inverter repair

It happens that the TV screen does not show, there is sound. In most cases, the snag is a backlight lamp, an inverter. It is logical to start testing from here. Due to the design features, it is difficult to get to the backlight, the determination of faults is started by an electrical circuit. Inverter. Find the presence of a transformer on the board, do not confuse it with the power supply( where the TV cable goes).

The input should be 12 volts, measure the value of the tester, check the integrity of the fuse. If you are burned, wait a little to rejoice, usually means something inside is broken. After submitting 12 volts, start checking with the presence of power in the dimmer circuit. Without it, the screen will refuse to glow. Voltage is zero - transistor switch is to blame. Correct the replacement of burnt items. Transistors ring short.

The permission signal is called Enable, supplied by the electronic board of the TV.Unplug the connector, apply 12 volts for power and 5 volts for Enable. Lamps caught fire - the TV board is faulty. Otherwise, continue to search. It is time to conduct an external inspection of capacitors, transformers, connectors enable the lamps. Defective parts are easily distinguished:

Resistor and transformer

  • Resistors are blackened.
  • Transformers fused protective film.

If a voltage surge appears on the lamp after starting the circuit, it is necessary to clean the contacts. It is useful to try to insert serviceable. High probability - the backlight will work again. It happens, the lamps will flash after turning on, immediately go out. Indirectly indicates a fault in the feedback circuit, or overload.

You should check the capacitors in the lamp branches, ring the transformer windings( zero resistance indicates a short circuit), then check the elements along the feedback circuit. Transistors, capacitors, diodes, resistors, other. It is important to know the peculiarities of the work of various microcircuits, in technical sheets usually admissible modes are indicated. It often helps to identify a malfunction with the usual scheme. Some items do not pull the load, create incorrect conditions.

The behavior described above, when the lamps, flashing, go out, is characteristic of the breakdown of the oscillations of the pulse-width modulator. At the output of the transformer is nothing. If you find a device for measuring frequency, connect a 100 kΩ resistor to the lamp connector. Oscillations of ultrasound and above( tens of kHz) should be recorded. Depending on the brightness settings, the frequency changes: with increasing it increases.

The measured parameters do not correspond to the nominal values ​​- the primary voltage generation circuit is to blame. After the inverter there are several elements of filtering / signal optimization. Chokes, transistors, resistors. Are checked in the usual manner for health. With unstable brightness, blinking suspicion concerns the central circuit of the TV, or pulse-width modulator.

Lost TV settings

It happens that the channel setting is lost. Chip TV memory in no way refers to the backlight. In this case, the screen ripples, the sound is missing. The TV is slow to show the channels, you should check the stock provider. Admire www.youtube.com/watch?v=YtqrIVaEDNI#t=11.The video says: without software updates, Tricolor TV channels will not be caught. The problem is easily eliminated by performing the specified actions.

Broadcasting is conducted in DBV-T2 format - channels are split by multiplexes. One frequency transmits many programs, the TV using the built-in adapter allocates information broken by frames, transforming it into a form that is digestible for the screen. The multiplex setting is lost, all channels that are part of are lost. Need to know the frequency of broadcasting. Corresponds to the digital television channel number. After you need to visit the TV menu, start searching for channels on the selected frequency. Upon completion of the operation, a list of stations caught, the signal level, quality should appear on the screen.

Sometimes the antenna is to blame. In our area, very often the cable is cut, especially the satellite cable. And at all with the purpose to hand over to the point of reception of non-ferrous metals, competition considerations. The action is very hard to track down and punish. Periodically, local providers are trying to crush the "heavenly", broadcasting by satellite. Tritely need to check the quality of the connection. In case of a break, the receiver will not see the converter or the disk.

We hope answered the question why does not show the TV, what could break, how to fix the attack. Now readers can find the fault themselves. Note that the backlight should be removed as gently as possible so as not to damage.

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