Benxi Unicom TV repair location TV has no picture and sound

Is the sound coming from the TV the sound from the TV station? There is no image. Is the on-screen setup menu not displayed?

At present, the simple working principle of TV is generally that the composite signal of image and audio broadcasted by the TV station is selected and frequency converted by the tuner to obtain the composite intermediate frequency signal, which is amplified and separated from the audio signal, and then amplified by low frequency. The speaker outputs sound; the image signal is amplified for the picture tube to display the image, and at the same time, the "synchronization signal" is separated from the image signal for the picture tube to stabilize the image (synchronized with the image transmission). After the external power supply is connected to the TV, a stable DC voltage is provided through the so-called "switching power supply circuit" for the operation of the "row output". The row output circuit provides power for the operation of various parts of the TV through transformers and rectifier circuits.

After powering on, there is only sound, but noise and no image. This may be a problem with the tuner and midrange amplifier. Generally, the picture tube should be able to display the machine setting menu at this time, with audio and video input. Interface, can play external audio and video signals.

There is normal TV program sound, which means that the high frequency, medium frequency, and sound circuits are working normally, and there is no short-circuit fault in the line output circuit. If the screen can display the TV setup menu, the fault may lie in the separation of audio to audio amplifier.

The sound is normal, there is no on-screen menu, and there should be no external video signal. Turn up the brightness and contrast (the remote control cannot be used normally, if there are adjustments on the machine), and pay attention to the screen performance. , shut down, if you can see a bright light flashing on the screen and a slight discharge sound at the moment of shutting down, the picture tube is generally not a big problem.

Open the back cover (pay attention to safety), turn on the power and check whether the filament of the picture tube is bright (failure of burned out filament is not common). Check the working voltage of each pin of the picture tube, especially the cathode voltage. This voltage should change accordingly. The brightness adjustment changes. If the brightness adjustment is extremely dark, the electron gun of the picture tube will hardly emit electrons and there will be no image.

Nowadays, almost all TV sets are equipped with remote controls and electronic control units. If the CPU chip fails, causing the brightness to be out of control, it is possible that there will be no picture.

In addition, motherboards are almost all made of monolithic integrated circuits, with centralized amplifier, audio and video processing, etc. in one circuit. If there is no corresponding information, it will be troublesome to check. Color TVs generally have three primary colors. A fault in one channel of the amplification circuit (mostly at the end of the tube) will cause abnormal color, and there is too little chance of all three channels failing.