Absence of colour on screen can be occur to many causes. Some sets will show only one primary color. Some others will show a plain white raster. Others may show a white plain raster. In all the above states, assuming that, the audio output is OK and let's see which might be the fault.
In a set, audio output is OK, means, tuner, video IF, audio output, power supply and all other parts are working fine, but there is some fault with the video section. Before going to troubleshoot, let's see what is happening in the circuit of the TV.
The TV transmission signals will contain these signal combinations. A carrier wave, which carries all these signal. The carrier wave will have a frequency. This frequency is usually called the transmitting frequency, as we say, that a particular TV station is tranmitting at 106.8Mhzs, 308Mhz, 609.3Mhz and so on. These frequencies only indicates the carrier frequency of the transmission. The carrier frequency is one, which carries, as it stats, more signals included in it, For sample, these signals will have synchronisation signals; both vertical and horizontal, which will be retrieved at the receiver circuits, seperates them, and makes the picture to a stable frame. The horizontal synchronisation signals helps to synchronise the picture horizontally and vertical signal stabilizes it vertically. We can't feel these signals are comming to TV, and are processing, becuse, among these two signals, one on the upper sider of the carrier wave, and the other will be at its lower part. Actually these signals are visible both at the left and right, top and bottom of the secreen, but will be scanned away from our visinity, when we see picture.
The other signals moldulated with carrier frequency is Luminance signal [actually a main part of video], Blue color signal, Red color signal. It should be noted that there is no Green signals are transmitted from the transmitter, and there is no such signal in the carrier wave too. Then how this green signals are produced?
Just see, there are actually three signals comes modulated with carrier wave R,B &Y. Here 'Y" stands for luminance signal otherwise, back and white part information to a particular screen. As you know, there is chroma processing Integrated Circuit, {IC}, in every color TVS. This IC have a matrix section inside and it compares the incoming R,G &Y signals. The comparison is done with resepect to Y signal. Thus the matrix section seperates [Y-R],[Y-B] . The resultant signals [voltage levels] are further processed to get the Green signal. Acually Green signal produced inside the TV itself and is the difference between [Y-R] & [Y-B], and it not supplied to it.
Let's check a set which have no Green color on screen. We know that the green colour is processed inside the TV circuit. If there is no green color, the picture will come appear ofcourse, but the color combinations will be strange, You will see a mixture of Red and Blue colors, as you know, all the colours we see are the combination of the three primary colors, red, green and blue. If any one is absent, abnormal color will be the result. Here we see some combination of colors on picture that both Red and Blue together can make. Zyan color for example. Actually, they toghther can make for color combinations.
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