مرحلة مكبر خرج الألوان .. كتاب التلفزيون الملون والعادي

18-20 stage color output amplifier:

These final amplifiers amplify the signals (B-Y) - (G-Y) - (R-Y) each signal by itself and in a special amplification circuit to reach the amplitude of the signal to a voltage ranging between (130-180V) in the color screen valve networks. Since the luminance signal reaches the cathode of the screen, the sum of these signals directs the beam of each projector and controls it to give a good color image on the screen.

These amplifiers are of the type of DC amplifiers that deal with the continuous component of the signal, because of its important role in improving the quality of the image on the screen and increasing its stability. Color signals may be obtained by using an external matrix, which amplifies these signals and sends them to the appropriate polarities of the screen LED and with the appropriate polarity.

Figure (30-20) shows an output amplifier of one of the primary colors in the Seronix FM120 device - and each amplification circuit consists of four transistors that connect the signal of each color from the integrated circuit (TDA3300) and reach the base of the transistor - the red color is its signal coming out from pole (20) for the integrated circuit. It connects to the base of the transistor BC307B (V603) via (R602-R601) and this transistor is connected in a common collector way to make compatibility between the output impedance of the primary amplifier for the red color inside the integrated circuit, and the input impedance of the output amplifier circuit for the red color in the two transistors (7610-7609). And we take the red signal from collector V610 (BF758) to the cathode (pole (8) in the screen, and the transistor (V615) which is (BF421) automatically adjusts the work of the red electronic launcher.

The other green and blue circuits are similar to the red signal circuit. The amplification circuits are fed from U1, which is equal to (250) volts, and from the voltage U62, which is equal to (8/11 volts). The zener diode regulates the voltage connected to the radiators of the transistors. As for the voltages of the cathodes of the screen diode, they are the same as those of the collectors of transistors (650-7630-7610), and this voltage is estimated at +150 (volts), and this voltage changes with the change of the illumination of the diode of the screen. Faults of some elements of this stage for one of the following manifestations:

1- The absence of one or all of the primary colors, with the appearance of return lines. The lighting may be absent after a short period of operation.

2 - Lighting the screen in one color red, green or blue with the appearance of return lines.

These malfunctions are caused by damage or a short circuit in one of the amplification transistors, a short capacitor or a unified one, or the absence of the feeding voltage. Or disconnection in one of the capacitors, and the defect may be in the integrated circuit V500 (TDA3300).
20-19 Automatic circuits in color television:

Most TV sets include some or all of the following automatic circuits: Color Adjustment (ACC) circuit: It is called Automatic Chroma Control circuit and is similar to AGC circuit in the channel selector and in the intermediate frequency stages (IF) - and in this circuit the color amplification is adjusted automatically, in order to ensure stability and consistency. The intensity and length of the color Fine-tuning circuit (AFT): It is also used in some monochrome devices - in which the medium frequency signal of the image is fed to the AFT circuit - if the frequency is incorrect, a correction voltage is generated that is fed to the voter oscillator, and it works to adjust this oscillator to secure a carrier frequency IF the image is correct. This leads to the best color or monochrome image

Automatic Frequency and Page Controller (AFPC):

Every color device has this type of circuit - the function of the AFPC circuit is to set the oscillator frequency (4.43 MHz) to be the same frequency as the color splash - this ensures correct color tint on the screen

Automatic Color Tint Adjustment (ATC):

When this switch is turned on, this circuit adjusts the color hue to a position that is pleasing to look at and watch, and this switch is useful when using a channel switcher, or changing channel programs significantly.

Automatic lighting control circuit (ABC):

We have previously explained the role of this circuit in automatically adjusting the lighting of the screen valve in proportion to the room light Automatic Lighting Limiter Circuit (ABL): This circuit determines the maximum lighting of the screen valve - and is useful in avoiding exceeding the lighting when the manual adjustment of the lighting is not correct.

Reference vertical interval (IR):

​​​​​​This circuit is useful in making the color saturation and hue adjustment fully automatic. Thus, when used, it gives the best quality in colors.