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3-7 Using an integrated circuit in the image detector:

Modern devices often use integrated circuits. The detection circuit is part of an integrated circuit used in the middle frequency stage of the image such as 440 TBA or T7607 or LA1357 in Sanyo Color - and represents a linear detector. While the binary is considered non-linear, which highlights some disadvantages, namely:

1- The binary has an effort barrier. It does not work unless it is exceeded, which is (0.6 volts) in the silicon diode type and 0.25 volts for the germanium diode - and the conductivity of the diode does not begin until after it receives 0.5 volts in excess of the voltage barrier - and this requires that the gain of the IF amplification circuit be About (80) (dB) and the antenna signal should be (100 microvolts) at least.

2 - At the low level of the signal, the work of the diode is in the non-linear part of its curve, and the non-linear element acts as a mixer that works on a frequency conflict for the signals entering it. They are the medium frequency that carries the image, the medium frequency that carries the sound, and the sub-carrier of the color signal, so it gives the sum of these frequencies in its output. Therefore, different frequency traps are set to neutralize some frequencies and prevent other frequencies.

3- The binary does not have any profit, rather it loses part of the signal, and this loss must be compensated by putting additional stages of amplification on the TV.

7-4 Synchronous Videos Detector:

A synchronous detector requires two different signals at its input. Figure (7-7) in contrast to the image detector diode. The two signals in the input are:
1 - Modified IF medium frequency signal
2 - A reference signal with the same frequency and page of the image IF carrier. This detector is part of an integrated circuit (IC). Among its most important advantages over other reagents are the following
1 - There is no voltage barrier that must be crossed, as in the detection diode.

2- It has a good profit.

3 - It is a linear element, which avoids the equal mixing of the input frequencies, thus producing different frequencies equal to their differential or quotient.

4- Provides a number of IF enlargement stages, as one stage is sufficient with some IF traps. due to its previous features.

5- Since no additional frequencies are generated in it because it is a linear element, there is no problem of re-broadcasting the frequencies in the voter and the antenna, which disturbs the neighboring devices. It does not require the existence of an FCC circuit to identify and prevent the spread of frequencies as in the binary detector.

The block diagram of a synchronous detector:

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​ ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​It is clear from the simplified box diagram Figure - (8) that this detector has two differential amplifiers shown in the diagram of the previous section - and two transistors modified. The first input of the reference signal is for the medium frequency carrier of the image, and it is entered in a push pill circuit to the differential amplifier - and the outputs of these amplifiers are connected in parallel. The result is a (push-pull) input and a parallel output. The two modified transistors have inputs (push-pull). Each of them is connected to the emitter of the differential amplifier to the ground, and thus they can change the output current of the two differential amplifiers according to the modulation of the IF signal - and this change in the current represents the original rate of the image identical to what happens in the transmission. The circuit is called "Synchronous Detector". Because it only detects IF modulation information that coincides in its frequency and page with the IF (picture) reference visual carrier. When the synchronization is correct, the detector only works to detect the modified frequencies. The frequency of the visualized IF carrier is canceled out in the differential amplifiers, which act as balanced detectors

7-5 Malfunctions of the image detector stage (visuals):

In monochrome televisions, we find that a malfunction leads to:

1- Loss of image or sound or both.

2- Synchronization glitch.

3- Weakness in the image, sound, or synchronization, if the duet has a partial malfunction that makes it not perform its work properly.

No picture or sound:

The possibility is a malfunction in the detector stage. The screen appears luminous and without an image - this indicates a decrease in the ratio of the forward resistance of the detection diode to its reverse resistance. Also, the presence of a weak image that is not improved by the contrast adjustment key indicates a malfunction in the detector diode.

Open in one of the peak files:

​​​​​​​The best way to detect this open is to short-circuit each coil in an appropriate manner
Wait and monitor the screen, if the image is not affected when the file is short. This indicates the safety of the examination area, and when the fault is detected, the file is changed to another similar one in all specifications.

Detector in colored devices:

When tracking detector malfunctions in color devices, the technician must be aware and understand the device diagram, since the sound signal is taken before the image detector, it is rare for the detector circuit to cause a sound defect, while the synchronization signal passes through the detector and then passes one or two amplification stages ( Illumination signal amplifier (Y), so the detector malfunction can lead to imbalance in synchronization and loss of image contrast, or a total loss of the image.But if the device contains integrated circuits, including this integrated circuit, it performs multiple functions in addition to an operation.It must be changed inevitably when any part of it fails.