Cont:2
In fact there is no need ot say, that audio informations also is being tranmitted along with these color signals withing the same carrier wave. It is also ther. But, the techneque used to transmit audio signal is different to that of color.
The video information is transmitted in AM [Amplitued Modulation} and audio with FM [Frequency Modulation]. Therefore, the video signal receved at the TV end may have some sort of noise, where audio will not have. More over, television signals cannot reach a vast area like radio signals. The reception will be best when we are in near visinity of the transmitter, and there is no obstruction to signals. In other words, the signals must be strong enough to overcome the noise, to get a clear and crisp reception.
Frequency Modulated [FM] sound signals are transmitted to different standards to different countirs. The standard used will said to 4.43; 5.5; 4.32 and so on. These are nothing, but indicates the position of audio signal, inside the transmitting envelope. For example, 5.5, means, the audio signal is transmitted 5.5MHz aprt from the video signal. going very deep into transmission technique is more confusing.
At the TV end, there must be sufficant signal strength at the antenna, to get a clear picture. The transmitted signals, comes in contact with antenna, comes to the tuner section of the TV. The tuner converts the very high frequency carriar wave along with video and audio signal, to an intermediate frequency, shortly [IF]. This intermedeate frequency is given to video IF stage of the TV and then detects out the video and sudio signals sperateley, gives to respective amplifiers to process. The audio signal will guided to audio amplifier to produce sound, and video signal is passed to video amplifier to process picture. Let we go very simple.
Come to our case. There is no Green signal to the TV under concern. As we know, there is no green signal transmission from the transmitter, and the matrix section inside the chorma ID derive this green signal and gie it to video ampllifier to process. This no means that the chroma section inside the IC is faulty. There might me some other reasons. We have to find out, whether such a reason is there, before confirming the IC has been damaged. This is the diificult part of service, not to this only, but for all electronic devices. Fault finding, point out the exact faulty section, locate the exact faulty component, the reaon for the failure of that component, etc- are the key factors, and a technician must know what he does with set, and must aware of its circuit diagram, its working and all otheres. He must be very patient, and well expereinced.
In fact, troubleshooting faults to an electronic equipement is an art.
If you come across the fault described above, lack or absence of Green color, the first test to do is to measure the voltage at the green cathode of the piclture tube. It is very easy to measure, as it is assembled and pluged onto the neck of the picture tube. You can see a square or rectangular printed circuit board pluged to the back side of the necd of the picutre tube.
Locate the Green cathode there. In normal cases, for all TVs, it will be marked on the base card, very near to respective pin as Gk,Bk&Rk. Gk-means Green cathode, Bk-means Blue Cathode and Rk-means red cathode.The easisest way to measure and compare the voltage is, measure the voltage of a good cathode which works fine. Here take the case of Red cathod[Rk]. There is no fault with it. It works fine, that is whey we see combination of red colors on screen.
Check the voltage at red cathode, It will be in the order of 270VDC to 189VDC. The voltage stated may vary a little. Mark this voltage on a piece of paper. Now measure the voltage at Green cathode [Gk]. It will have much difference between the voltage to other two cathodes; no doubt.
Here starts the play. To proceed , you must have sound knoledge in electronics, or anybody at your home must have. I'll give more details about troubleshooting, somewhere after in this blog.
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