استعادة المركبة المستمرة dc في التلفزيون الملون .. كتاب التلفزيون الملون والعادي

10-5 DC Component Recovery in Color TV:

The recovery or recovery of the continuous component is also necessary in color television as in black and white - and necessary for the visual signal entering the screen. DC reference voltage to form the image of the required quality - but the DC component of the visual signal is lost in the interconnect capacitors. As for the colored one, where the visible signal is called the luminance signal (Y) - if the connecting element between the circuits is capacitive - then the problem will be similar to the visual signal in black and white - and requires a circuit to retrieve this continuous component like the one used in black and white. Figure 6-10 shows the passage of the luminance signal in the color TV - through the stages of the image amplifier - and the delay line whose function is to keep the luminance signal on the same page as the color signals that must pass through the different stages of amplification. If capacitive linkage is used in any amplification circuit, then there must be a circuit to retrieve the continuous component.

In Figure (10-6), which shows the previous box diagram, the color signal is taken from the first image amplifier and fed through the bandpass amplifiers and then the color processor - and here the circuits differ according to what the manufacturer prefers - however, most of the devices have Bandpass amplifiers. They are simply tuned amplification circuits that pass only color signals that approximate the color subcarrier frequency, which is (3.58 MHz) in NTSC and (4.43 MHz) in PAL and SECAM.

Chroma box chart:

The box diagram shows Figure (10) - (7) color phases - and the Color Killer voltage regulator prevents the beam amplifiers from generating any output signal when there is no reception of the color carrying signal. When there are colored signals, it works as an automatic switch that operates the amplifiers. As for the beam amplifiers, they deliver color signals to three modulation detectors, one of which is concerned with one of the three primary colors (RGB). At the same time, the reference (4.43 MHz) signal is also fed to the modulation detectors - and each signal coming out of the modulation detector is amplified before it reaches its network at the screen valve. These latter amplifiers are connected capacitively. Therefore, a circuit must be used to retrieve the continuous vehicle - and this is what is noted in the block diagram - where there is a clamp on the output of each color circuit that works to retrieve the DC vehicle. And since there is no synchronization or erasing signal in the color signals to serve as a reference - therefore, a circuit is placed as an artificial reference, which is the amplifier circuit and the continuous composite return, as in the figure
(10 - 8). In the circuit, we find that each network has an independent stabilization circuit that deals with its own signal - while the circuit of the amplifier or continuous vehicle return, it includes the three networks.
​​​​​​The negative pulse from the output horizontal transformer (Flyback) is fed to the emitter of the stabilizer or return amplifier. (Q101). And make this transistor in the case of conduction during the time of the negative pulse only - and the diode (D101) removes any positive part of the horizontal output transformer signal.

The file (L101) damps the radiation from this circuit. The amplified negative pulse appears through the bias of the screen valve, and the resistance (R104) proves it to the maximum value of 180 volts by means of a diode zetter (D102). The negative part of the pulse voltage is applied to each of the three stabilizing diodes (D105, D104, D103) DC recuperators, which determine the position of the photo valve bias control. The action of the stabilizing diodes makes the three grids in the color screen initially fixed on the pulse voltage bias, which is at least 80 V. In the diagram, only one color amplifier is shown in detail, and the other two color amplifiers are connected to the stabilizer circuit in a manner similar to the first.
When color signals pass through junction capacitors at the output of each Chroma Amplifier - such as capacitor C103 in the Q102 collector circuit - the DC level is disturbed and lost. It is necessary to ensure that the DC component is retrieved individually for each color grid - so that the correct luminance value for each color can be obtained. This method is similar in principle to what we explained in the composite visual signal in monochrome television. Thus, each color signal causes its own two-mode connection. So charge and discharge capacitor delivery specified for it. For example (C103) for the (R-Y) amplifier - and thus the value of illumination for each color changes independently and according to the incoming color signal and related to it as it was in the image captured by the imaging camera.

6-10 Faults in DC Component Recovery Circuits Since continuous component recovery affects the bias voltage of the monitor diode - it is logical that a defect in the DC recovery circuit can completely disrupt the appearance of the image or spoil the lighting or both - even if it changes the value of an element of the circuit It may disturb the level of the continuous component - if the screen bias voltage does not change properly appropriate to the change in the continuous component value of the image signal (possibly a circuit fault), the background of the image will appear darker - as may occur loss of contrast - and if we increase the lighting

With the lighting control switch, the vertical return lines become visible. In color TV, a DC regenerator malfunction may occur in the luminance Y circuit, as it may happen in the color circuits - if the defect occurs in the luminance circuit only, then the contrast weakens and this weakness is clear in the monochromatic device - but in the color device, the colors weaken when they appear on the screen. Poor contrast appears when viewing black and white images and scenes. But if the fault is in the circuit of one color - it may lead to a complete loss of this color or it appears dull.

The DC voltage in the screen valve cathode and network should be measured when there is doubt about the DC vehicle recovery circuit - a fault in the recovery circuit causes the DC bias to change in the electronic implosion of the faulty circuit.