“General black-and-white TV sets are assembled by purchasing three pieces of JG-988-type parts. The main feature is that the image channel uses the integrated circuit μPC1366C, the sound channel uses the μPC1353C, the field scan circuit uses the μPC1031H2, and the power supply circuit and the line scan circuit use discrete components.
General black-and-white TV sets are assembled by purchasing three pieces of JG-988-type parts. The main feature is that the image channel uses the integrated circuit μPC1366C, the sound channel uses the μPC1353C, the field scan circuit uses the μPC1031H2, and the power supply circuit and the line scan circuit use discrete components. Among them, the integrated circuit μPC1366C contains functions such as image mid-amplification, detection, pre-view amplifier, noise suppression, AGC voltage detection, mid-amp AGC, high-level AGC amplification, etc.; μPC1353C integrated circuit has audio mid-frequency limiting amplification, frequency discrimination, and Electronic volume control , Audio pre-amplification, power amplification and internal voltage regulation functions; μPC1031H2 integrated circuit is mainly composed of field scanning oscillation, sawtooth wave formation, field driving and field output. In this way, the peripheral components of the public channel, the sound channel and the field scanning circuit are less, and the installation and debugging are easier. The power supply circuit and the line scan circuit are composed of discrete components, which can train students’ installation and debugging skills, so the use of this model of movement is more suitable for schools to conduct black-and-white TV installation and debugging teaching.
In the specific training, the installation and debugging of the machine can be carried out according to the following steps:
1. Detection components
There are many components in the TV, and once used wrongly, it is easy to cause the circuit to work poorly or cause malfunctions.
①. Resistance detection: Most of the resistors used now are color ring resistors. First, let the students arrange all the resistors, stick them all on the paper with transparent tape, write the resistance value beside the resistor according to the color code, and finally check it with a multimeter. High-power resistors are marked with special symbols.
②. Capacitor detection: Arrange the capacitors of the same model and fix them on the paper. Write the capacitance and rated voltage beside the capacitor according to the symbol marked on the capacitor. Some manufacturers mark 103, 332, etc. on ceramic capacitors and mica capacitors. 103 means 10×l0 (cubic) = 10000pf, 332 means 33×l02=3300pf. 3n3 means 3300pf, etc., these must be identified by the students themselves .
③ Detection of diode: According to the nature of forward conduction and reverse cut-off of the diode, it is easy to detect the quality of the diode with the resistance file of a multimeter. Students can also be guided to detect the polarity of the diode by connecting two ordinary batteries in series with a flashlight bulb. When the anode of the diode is connected to the positive end of the battery, the bulb will light up and the diode will be on. Otherwise, it will not light up and the diode will not be on. Students using this method are more intuitive and can arouse students’ interest in learning. In the use of diodes, the power supply rectifier circuit current is large, and surface contact diodes should be used; point contact diodes 1N4148 for line AFC and field flyback circuits; FR fast recovery diodes for boost and line damping.
④ Judgment of the polarity of the triode: (a) Judgment of the base. Use a multimeter R×100 or R×1k to measure the forward and reverse resistance values between every two of the three electrodes of the triode. When the first test lead is connected to a certain electrode, and the second test lead touches the other two electrodes successively and both have very low resistance values, the electrode connected to the first test lead is the base electrode b. At this time, pay attention to the polarity of the test lead of the multimeter, if the red test lead is connected to the base b. When the black test lead is connected to the other two poles, the measured resistance is small, and the tested transistor can be judged to be a PNP type tube; if the black test lead is connected to the base electrode b and the red test lead is in contact with the other two electrodes, the measured value is If the resistance is small, the transistor under test is an NPN tube. (B) Determine the collector c and emitter e. (Take PNP as an example) When the multimeter is placed in the R×100 or R×1k gear, the red test lead is connected to the base electrode b, and the black test lead is used to touch the other two pins respectively, the measured two resistance values should be one large Some, a smaller one. In a measurement with a small resistance value, the pin connected to the black test lead is the collector; in a measurement with a larger resistance value, the pin connected to the black test pen is the emitter. When judging the polarity of the transistor, students can also use the method of connecting the battery to the flashlight bulb. Connect the battery terminal to one pole of the transistor, and connect the other end of the battery to the bulb to the other two poles. If the bulb glows, start One pole connected is the base b, (the one that is not moving is the base), and the other two ends are the collector c and the emitter e. If the positive terminal of the battery is connected to the base, the transistor is of NPN type, and the negative terminal is connected to the base, then the transistor is of PNP type. The method to distinguish the collector and emitter is (take NPN blue pole tube as an example): connect the two poles positive and negative to the circuit connecting the battery and the bulb in series, and connect a 100Ω resistor to the base and the positive electrode of the battery. If the bulb is shining on one pole, then one pole connected to the resistor is the collector, and the other pole is the emitter.
The detection circuit is shown in the figure below.
⑦. Detection of sound circuit:
(A) In the power supply loop of the multimeter, the current should be 30mA when the volume is the smallest, and about 200mA when the volume is the largest.
(B) Adjustment of frequency discrimination characteristics: Under normal circumstances, the adjustment of frequency discrimination characteristics is mainly realized by monitoring the sound quality of the accompanying sound. Use a non-inductive screwdriver to adjust the position of the magnetic core of the frequency discrimination coil to make the sound quality reach the best condition. If adjusting the frequency discriminator coil can not make the sound quality reach a more ideal state, you can also adjust the magnetic core of the fine-tuning Inductor to make the picture sound effect better.
4. Overall adjustment of the whole machine
After the circuit of each part of the whole machine is assembled, although step-by-step debugging is carried out, it is necessary to carry out the overall adjustment of the whole machine in order to further improve the overall quality of the whole machine. The overall adjustment of the whole machine is divided into (1) debugging of the power supply part; string an 80-meter multimeter at the AC 220V power fuse (primary side of the power transformer), the AC current value should be about 130mA; string in the fuse after rectification and filtering The DC current of the multimeter should be 1N12A after power-on; adjust the sampling adjustable resistance so that the output voltage of the power supply is 12±0.2V, and the ripple voltage is less than 2mV.
(2) Check the synchronization range, brightness and contrast to receive TV programs, adjust the horizontal synchronization and vertical synchronization knobs, so that they can be synchronized normally and the synchronization range is sufficient. Adjust the brightness and contrast knobs to make the adjustment direction consistent with the changes in brightness and contrast, and place the adjusted knobs in appropriate positions.
(3) Adjustment of the deflection yoke Adjust the deflection yoke so that the image is not skewed and is at the center of the screen.
Place the deflection yoke close to the cone of the picture tube so that the four corners of the screen do not appear dark corners.
(4) Adjustment of cathode current of the picture tube Adjust the brightness potentiometer to make the cathode current always change between 10~120μmA.
(5) Line linear adjustment Adjust the line linear coil to make the size of the black and white squares uniform, and the difference between the widest and the narrowest squares should be less than 10%. If the adjustment of the line linearity still fails to meet the linearity requirements, the S correction capacitor can be changed. The method of capacity is adjusted.
(6) To adjust the line width, use the TV to receive the test card of the TV station, and there should be 2 to 1.5 grids on the left and right; when receiving the checkerboard signal, there should be 16 to 17 checkerboards in the horizontal direction.
Excessive width of the line will cause the TV image test card to become a flat ellipse, resulting in line distortion and reducing the image content. The adjustment of the line width can be carried out by changing the flyback capacitance. If the line width is large, the flyback capacitance can be reduced; if the line width is insufficient, the flyback capacitance can be increased.
(7) Adjustment of synchronization range
①, line synchronization adjustment. When adjusting the horizontal oscillation coil, the horizontal frequency can still be synchronized within the range of 3 to 4 laps left and right, but the image only moves left and right. Adjust the horizontal frequency coil to the middle position, and then turn it to the left or right one circle. When the channel is changed, there should be no line out of synchronization.
②. Field synchronization adjustment. Adjust the field synchronization potentiometer so that when it rotates to the bottom to the left, the field is always synchronized; when it rotates to the bottom to the right, the image starts to roll downward.
(8) Field linear adjustment Adjust the field linear adjustable resistance to make the black and white checkerboards symmetrical up and down, uniform in size, and the amplitude difference between the squares should be less than 5%.
(9) Adjustment of the field width When receiving the TV test card, when the field amplitude potentiometer makes the field amplitude full, there should be a margin of about 0.5 to 1 grid each on the top and bottom, or when a black and white checkerboard is used, there should be 13 in the vertical direction. ~14 checkerboards.