طريقة تتبع وكشف اعطال جهاز التلفزيون الملون والعادي ١_a .

21-3 Method of tracking and detection of normal and color television set malfunctions:

The logical method or approach must be followed to analyze any defect or malfunction in the television equipment and to follow up on the cause that led to this defect. This logical sequence is suitable for dealing with the malfunction of any electronic device, provided that the person has knowledge and awareness of the operation of the device and its stages, circuits and plans.

1- Observation: which is the use of the sense of sight, hearing and smell in the first step:

For example: Is there a monochrome or color image? If so, is it good or is it defective? Is the sound normal or is there something wrong with it? If there is no defect or defect in it, then what is the type of defect or distortion? And use the sense of smell to detect the presence of a high-temperature or burning element. This may lead to the identification of the influencing factor and the cause of the defect.

2- Determining the stage in which the defect is: this is the second step - and observation may indicate it, for example - if the image is not in sync horizontally, then this usually indicates the presence of a defect in the stage of horizontal deviation, and if the colors of the image are present but they are not correct, then this indicates a malfunction in the Color phase (chroma).

3- Determining the circuit in which the malfunction occurs: After determining the stage in which the malfunction occurs, we proceed to identifying the malfunctioning circuit. This may require a signal injector or a signal plotter with the use of measuring voltages and resistors.

4- Identification of the faulty component: The circuit components in which the fault is confined are searched - the research may require the use of an ammeter for the voltage field (volts) or the resistance field (ohms) and the use of a transistor tester - and the screen valve is checked and tested with the previously mentioned screen tester.

comments :

1 - It is very important not to follow the method of trying to simply replace parts, so that we may end up replacing the broken element by chance. This method may cause an exacerbation of the defect and malfunction, in addition to being a waste of time - but the logical approach must always be followed to detect the phase, circuit, and the component causing the malfunction.

2- Make sure first that the defect is not caused by misconfiguration or calibration - the presence of buzzing with the sound may be caused by misadjustment of the FM audio signal detector - and incorrect tuning of the AGC circuit may appear snow spots in the image, overloading the image, or poor synchronization.

21-4 How to count the failure stages by observation:

After the technician understands the working principle of the device, the stages of passage of the visual and audio signal, the horizontal and vertical pulses, etc., and in practice, he has a good sensitivity and a correct opinion to limit the location of the malfunction, and he can be guided by the box diagram for that. For example, if the defect is in the image and sound together, it clearly appears to the technician that the defect lies in one of the common phases that both the sound and image signals pass through. It is located in an area that precedes the point of separating the sound from the image - between them. A defect at a point after separating the two signals and within the phases of the visual signal, and the same case applies if the distortion or defect is in the sound only, then this means that the malfunction exists in the phases of the sound only. Any distance detector. Thus, the faults can be classified into:

A - Distortion of sound and image are normal.

B - distortion of the image and sound is normal.

C - Distortion of sound and image together. Look at the box diagram in Figure (18-21) and (19-21).

After identifying the stages in which the fault is confined, one must return again to the device's box diagram. In the image section, we find that its stages are the IF amplifiers - the image detector - the image amplifier - and the horizontal and vertical scanning stage - and the high voltage stage feeding the screen is located after the horizontal scanning output stage. In the diagram We find that stopping the signal at points A, B, or C will prevent the visual signal from reaching the screen. If the sound separation point is located outside the defect area, the sound will not be affected. But if it is located in the defective area, the sound will also be lost. In both cases, the linear structure (raster) appears on the screen. Another example: If we assume that the circuit is open in D according to the diagram in Figure (19-21), the synchronization pulses will not reach the scanning oscillators, and thus these oscillators will not adjust or control the signal. next, while the image signals continue to arrive. out of sync. The sound is not affected by this defect and remains normal.

We will show more clarification of the specific malfunctions in addition to what we have presented and explained in the previous chapters regarding the malfunctions of each of the main stages of the television set.

Determine color defects by observation:

We will return to the explanation of color malfunctions in another paragraph, and here we will only look at determining the location of the color-related malfunction in general by noting the image on the screen.

Among these faults are:

1 - There are no colors, but the picture is in black and white.

2- Weakness in color intensity or color strength.

3 - Loss or weakness of color synchronization. .

4- The color hue is incorrect, and by returning to the simplified box diagram of the color circuits in Figure (21-20), it is possible to follow up and determine the location of the malfunction.