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9-11 Malfunctions of the image amplifier circuits:

We will now mention the faults related to black and white television with regard to the image amplifier circuits. As for the colored device, it will be mentioned in the chapter on general faults. The figure shown (25-9) shows the model of the station’s badge when the device is normal and has no faults. The vertical lines are noticed in the upper part of the badge, and indicate the frequency response curve higher than (3 MHz). It also notes the good contrast and the absence of any smudges in the The clear details in the letters of the words and the large areas indicate the correctness and safety of the response curve for low frequencies.

phenomenon:

No image:
​​​​The possible reason is that the image amplifier stage stops working between them. The linear structure (raster) appears intact and good, as in Figure (9-26). It is possible that the malfunction causes a defect in some of the voltages feeding some stages, or a weakness in a transistor or a valve - or A defect in the photodetector due to an opening in a connecting capacitor, an opening in the peak coil, or a break in the printed circuit connections

Weakness in the high-frequency response: Compared to the station sign in the first figure (9) - (25), we find that the upper vertical lines have been blurred and almost do not appear - due to a lack of high-frequency response as a result of a defect in the image amplifier or the middle frequency of the IF image, as in Figure (9 - 27)

This is indicated by the blurring of the vertical lines in the upper half of the insignia at the frequency (3 megahertz). The vertical lines may blur near the lower half at the frequency (2) megahertz. Also, the high frequencies of the image are responsible for showing the details of the small elements of the image. This malfunction is evident when the fine details of the TV image are not clear and it appears as if it is a very enlarged image. The viewer notices that the letters separating adjacent light and dark areas are almost invisible
It is also difficult to read the small letters written on the badge, and this gives an impression similar to lack of proper focus (Focus). In this case, the horizontal lines appear well focused, and this negates the failure of focus. And the possibilities contained in the poor response of high frequencies are: a defect in the peak coils - a defect in the passing capacitor - replacing the transistor with a type that is not identical to the original - increasing the value of the load resistance - a defect in the parallel capacitor in the image detector.


Poor low frequency response:
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They are the frequencies less than (100) kHz - which are responsible for shaping and showing the larger areas of the image clearly, as well as the integrity of the contrast - when the response of low frequencies is insufficient, the image appears weak features and poor contrast. It may not show smudges, but the weakness and accuracy of the image remains the same.
As for increasing the response more than required for low frequencies, it gives an excess in contrast and smudges in the image, as shown in the previous figure, and the image appears blacker as it appears that the shaded areas in the middle circle of the emblem are almost blending with the neighboring areas, in addition to that the horizontal wedges appear more Darkening from the vertical wedges, and this is another indication of poor low-frequency response. Poor low-frequency response may be caused by a defect in the connecting elements, especially in the connecting capacitors, and the biggest possibility is also a defect in the low-frequency compensation circuit, especially the circuit capacitors

No picture and sound is normal:

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Bold buzz lines in the picture:

And the shape (۹ - ۲۹) shows the tinnitus lines with frequency (50) Hz) - and this phenomenon is usually caused by the overlapping of alternating voltage (50) (Hzz) in the phase of the image amplifier.
In older devices, there is a possibility of leakage between the heating filament and the cathode in the valve - between them this does not happen when using transistors in the image amplifier. 100 Hz interference occurs in the types of devices when the DC filter feeding the circuits is insufficient - and the 100 Hz interference phenomenon is similar to the figure in the picture - but with two broad lines in the screen. We must note that this interference, whether it is 50 Hz or 100 Hz, may cause interference in the stages of high frequencies (RF) or medium frequencies - IF - in the detector stage, but it may reappear on the screen as in the figure.