Monday, June 20, 2011

PICTURE IS OK AND THERE IS NO SOUND IN TV?

There are some occations arise when picture in a TV will be OK while absensce of sound.
Picure is OK, means that, functions upto tuner to video output, including power supply are OK. The absence of sound may be either the fault to its speaker or speakers. In some sets there will be two speakers connected in series connection, and its sound output will be MONO. In these type of sets, if the connction is done as above, even one speaker has gone out [that is its voice coil or its connection gets opened, both speakers will not work. In this case, you have to check each speakers individually for coil conitnuity, and the faulty one must be replaced. If there is no fault ot the audio amplifier section of that TV, the problem will be solved with this.
In stereo sound system TVs, two of its speakers will have individual amplifiers, some may have both amps integrated in one IC or two ICs are used seperately for each channel. In this type of sets, absenece of sound can be either to the fault of the failure audio output IC or its supply line voltage. In most cases, you can make sure the reason with a simple test without opening the set. Place your ear very close to its speaker side, and switch ON the set by its front panel power control switch. if a "Thumb' sound is heard form the speaker, you can confirm that the speaker is OK, and the power supply is comming to the output IC. If so, check the output IC terminal solderings for some loose contact. During long run, this may happen because, the Audio Output IC will heat up during working, and repeated heating and cooling may make loose soldering at its terminals. In most cases this is found a common fault. to rectify this, you have to open your TV, and pull out the audio output card, place it upside down, and resolder all the terminals of the output IC by applying a little more solder, without making any soldering bridges in between terminals of the IC. If this also doesn't help you, check the input voltage of the audio output IC. In most sets there will be a fuse resistor used as protection, will be in 0.2Ohms in value, and will get opend thus disconnect the supply. This will happen when the output IC itsef get shorted. If you see this resistor opend, check the output ICs positive supply rail terminal to the negative terminals' rresistance with the help of an Ohm meter, if foud )Ohms, make sure that the IC has got damaged. Here you have to repalce the IC and this fuse resistor too.
There is an other possibility too, is, the audio filtering stage in the video IF stage get faulty. To detect this, you have to go to the VIF section.

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