الأعطال في دارات الخرج الرأسي .. كتاب التلفزيون الملون والعادي

15-10 Faults in the vertical output circuits:

It is often not difficult to distinguish and limit the perfumes of these circuits. Examining the image on the screen accurately shows and determines the location of the defect. When dealing with faults in the vertical output circuits, we must bear in mind that their main function is to secure a linear scanning current of sufficient width for the deviation of the beam. In color devices, the task of vertical matching is added to that function. And on the basis of these functions, the phenomenon of malfunction can be clear in the image specifications such as height - linearity - congruence - turning off the return line - and these malfunctions are similar in color and monochromatic devices. It excludes the matching function.

Elevation faults:

Line and include the total loss of vertical deviation. This fault appears with a bright horizontal presence in the center of the screen. Figure (21-15) Vertical deviation work - If this bright line is left for a long time, it may burn the phosphorescent layer inside the screen. This damage does not occur if the service key is used because the electron beam intensity is low.

And the possible cause of the total loss of vertical deviation and the appearance of a bright line in the middle of one of the following faults:

1- There is no input signal from the vertical oscillator or its corresponding digital circuit.

2- Loss of operating voltages in the output circuits.

3 - The failure of the output transistor LED in the old types

4 - Malfunction of the vertical output transformer.

5- An opening in the connecting capacitor.

6- An opening in the valve cathode circuit or the transistor radiator circuit. .

7 - Open circuit in the deflection coils

8 - Shortness in both coils of vertical deviation.

As for the other faults of the height, they include the insufficient height of the image - or distortion in the image and its compression in one of the sides. The reasons for the decrease in the height of the image are: Increasing the value of one of the resistors in the path of the DC supply voltage and increasing the resistance reduces the magnification of the stimulus stage or the output amplifier - and the weakness or damage of one Transistors weaken the amplification. As for the weak operating voltage, it can be ruled out if the rest of the circuits of the device are working normally, and the phenomenon of image distortion may be due to a short circuit in one of the two vertical deflection coils. One healthy file is not sufficient for the complete deflection of the beam - and the short may be in the damping resistance that forms the vertical deflection coils. The occurrence of shortcomings in the deviation files requires changing these files.

Linear faults (straightness):

In Figures (15-22) we find the effect of linear and non-linearity on the screen scan lines. In Figure 8, we find that the linearity of the scan makes the distance between the scan lines equal throughout the entire screen. In Figure B, the increase is regular until the lower part of the screen, where the horizontal lines are crowded in a way This is due to the non-linearity of the positive part of the wave current.

Figure C is the opposite of Figure B, that is, the lines are more crowded in the upper part of the screen, then the lines are spaced in the lower part.
The main causes of non-linearity in the vertical output circuit are:

1- Changing the value of a resistance or a capacitor in a generation circuit of the saw.

2- A defect in the feedback files.

3- A change in the bias of a valve and a transistor.

4- An opening in a connecting capacitor.

In the survey circuits, it is generated from the saw in the RC circuit according to the time constant of the circuit - every change in the value of the capacitor or resistance changes the time constant of the circuit - and changing the bias of a transistor or a valve in the circuit may make its work non-linear - and in modern devices the circuits are provided with feedback To correct the linearity defect, the faults of these circuits may change their efforts and make them non-linear, and the source of these faults may be a short circuit or a leakage in one of the connecting capacitors

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