The first thing to do with this type of fault, is to check the speaker of the TV. If the voice-coil of the speaker has got damaged, there will be no sound output from it, even if it gets sound output signals from the audio amplifier section of the circuit board inside the TV. you can check the speaker very easily. Just take a good dry-cell, connect its two poles [+ve and --ve], with tow pieces of wire, and touch the the other end of these wire to the two terminals of the speaker connection terminals. If the speaker is good, you can hear a 'dub' sound from it for each intermittent touches. If you can hear this sound, speaker is OK, and the fault lies in between the speaker connection terminals to the amplifier section of your TVs circuit board. In almost all TVs there will be an earphone socket or a headphone socket connected in between the main power amplifier section of the TV and the speaker. When we push in an earphone pin or headphone pin into it, the internal flip connection will change over [cut and change] to earphone or headphone, and the connection to speaker is terminated. In some occasions, even after we pull out the inserted pins from the socket, the internal changeover connections may not engaged properly, and a break in connection may occur, thus the audio signals will not come to loud speaker. Check the connection of this earphone [headphone] for any fault.
Just connect a good headphone to this socket and listen whether there is sound output can be received by it. If you get sound output, and not from the speaker, when you unplug the headphone pin from the socket, and the speaker is found OK, replace the headphone socket with a new one of same type. the fault will be rectified.
If you do not get sound from both speaker and headphone, the audio amplifier section of your TV's circuit board should be faulty. There are two main faults which can occur to this circuit. The first one is with a faulty audio output device. In most present TV,s, this section is composed of integrated circuits, in short ICs. The audio output IC will be screwed onto a metal heat-sink, to radiate heat from it while it works. Some may not have heat-sinks and wil be soldered directly to the printed circuit board. In most cases, the IC will be screwed on to a heat-sink. You can detect this audio amplifier section, by following the speaker wire. The wire to the speaker will emerge from this section. Before doing anything, first check the solder terminals of this IC. It is a common fault that, soldering loose may occur to this IC's solder terminals. As the IC heat up while it works, the terminals of this IC will also heat up. Repeated heating and cooling can make solder terminal joints to get loosed. Normally, these loose solder points are very difficult see, as it may be microscopically small. It is best to resolder all the solder terminals of this IC, by applying a little more solder, without making any solder splash short in between adjacent solder terminals. Just use a 20 or 25 Watts soldering iorn with pointed tip to so this work. If you are familiar with using de-soldering pump, just resolder all the solder from these terminals, and resolder all of them with fresh solder, and it is the best way too.
If this also does not help you, just measure the input voltage of this IC. If it is not here, check the track that supply voltage to this IC. Normally, there will be a small value serial resistor connected to this supply rail, which may fuse out, if the IC has some internal short with it. If so, before replacing it, measure the resistance of the positive supply pin of the IC with respect to negative line. the resistance must not be below 25 Ohms or so. if it is found approximately equal to zero, or much below 15 Ohms or so, make sure that the output IC is faulty and should be replaced with same type and number.
Before replacing the IC, just measure the resistance of the positive terminal to negative, once more. If it is found to be very low as said above, some other shorted component is there. Check the ceramic capacitor, connected if any, with the positive supply rail of the IC. This is a common fault, as ceramic capacitors will get shorted making a dead short circuit, thus cause the fuse out of the current limiting resistor said above.
So it is best to sully the set after de-solder out the output IC from circuit, and see whether the limiter resistor will blow out or not. if blow out, check the reason for this fault. If this happens, the IC you have de-soldered out from the board may good, and the fault was with other component, like ceramic capacitors, or even shorted electrolytic capacitors.
To 95% cases, the audio output IC has found faulty, by my service experience.
Just connect a good headphone to this socket and listen whether there is sound output can be received by it. If you get sound output, and not from the speaker, when you unplug the headphone pin from the socket, and the speaker is found OK, replace the headphone socket with a new one of same type. the fault will be rectified.
If you do not get sound from both speaker and headphone, the audio amplifier section of your TV's circuit board should be faulty. There are two main faults which can occur to this circuit. The first one is with a faulty audio output device. In most present TV,s, this section is composed of integrated circuits, in short ICs. The audio output IC will be screwed onto a metal heat-sink, to radiate heat from it while it works. Some may not have heat-sinks and wil be soldered directly to the printed circuit board. In most cases, the IC will be screwed on to a heat-sink. You can detect this audio amplifier section, by following the speaker wire. The wire to the speaker will emerge from this section. Before doing anything, first check the solder terminals of this IC. It is a common fault that, soldering loose may occur to this IC's solder terminals. As the IC heat up while it works, the terminals of this IC will also heat up. Repeated heating and cooling can make solder terminal joints to get loosed. Normally, these loose solder points are very difficult see, as it may be microscopically small. It is best to resolder all the solder terminals of this IC, by applying a little more solder, without making any solder splash short in between adjacent solder terminals. Just use a 20 or 25 Watts soldering iorn with pointed tip to so this work. If you are familiar with using de-soldering pump, just resolder all the solder from these terminals, and resolder all of them with fresh solder, and it is the best way too.
If this also does not help you, just measure the input voltage of this IC. If it is not here, check the track that supply voltage to this IC. Normally, there will be a small value serial resistor connected to this supply rail, which may fuse out, if the IC has some internal short with it. If so, before replacing it, measure the resistance of the positive supply pin of the IC with respect to negative line. the resistance must not be below 25 Ohms or so. if it is found approximately equal to zero, or much below 15 Ohms or so, make sure that the output IC is faulty and should be replaced with same type and number.
Before replacing the IC, just measure the resistance of the positive terminal to negative, once more. If it is found to be very low as said above, some other shorted component is there. Check the ceramic capacitor, connected if any, with the positive supply rail of the IC. This is a common fault, as ceramic capacitors will get shorted making a dead short circuit, thus cause the fuse out of the current limiting resistor said above.
So it is best to sully the set after de-solder out the output IC from circuit, and see whether the limiter resistor will blow out or not. if blow out, check the reason for this fault. If this happens, the IC you have de-soldered out from the board may good, and the fault was with other component, like ceramic capacitors, or even shorted electrolytic capacitors.
To 95% cases, the audio output IC has found faulty, by my service experience.
