When we are doing maintenance, we always hope that the circuit is simpler and more normal, so that the board will not feel upset when it is repaired. However, most of the cases are not likely to be imagined by the individual. How many kinds of boards are there, and how many kinds of circuit styles there are, then we need to accumulate maintenance experience and strengthen our theoretical cultivation. Once you have fixed a thing, you will often feel a sense of openness.
Now take a CRT color TV circuit diagram to say things: (refer to a post on the "Longxing World ACE" netizen yesterday)
A Konka P2902T high-definition color TV (applicable models: P2908T, P3460T, P3409T, P2903T, P3618T, P2906T, etc.), no high voltage, +B voltage 150, 200v voltage 150, acceleration stage voltage 0v, filament bright, no grating, related circuit See Figure 1, Figure 2.
In fact, many people are wondering: "This is not scientific!" +B voltage is normal (note, the nominal voltage is 150V), the filament is bright, the line should be oscillating, but there is no high voltage, no acceleration voltage, and The line did not start. Going to the hospital for medical treatment, the change should be the key suspect, first killing the change and then talking. And slow, let's see where this filament voltage comes from (see Figure 1). The current is output from the output of the switching transformer 1 pin. After two steps of depressurization, it becomes a DC 6.3V and is sent to the picture tube, and the winding of the 8-pin filament is useless.
To figure this out, the problem is simple. We can't start with the line (see Figure 2). The line does not vibrate. Generally speaking, the object is suspected to be line power supply, line pipe, row change, reverse process capacitor, S correction capacitor, damper diode short circuit, open circuit or bad cause. It can be determined by disconnecting the ground resistance value. If there is no problem, go ahead and check the transformer part, push the tube, then check the shock supply, the large part of the oscillation, and the output part of the pin voltage waveform to determine, if there is no problem, it should be the bulk itself. (The relevant circuit is shown in the attached PDF according to the specific model)
Then analyze an example of this model "three no faults" (see Figure 3 for related circuits):
After inspection, the insurance and switch tube are damaged, and R918 is open. After the replacement, for safety reasons, disconnect the inductor L905 and connect the dummy load test machine, the bulb lights up, and the +B output 142V is normal. When the inductor is connected, the raster appears and the image is normal. Turn on the machine for about five minutes, only listen to the sound, the picture is completely absent, the insurance and the switch tube are damaged again.
In actual repair, the switch tube operates in a high current state and is mainly controlled by the N901. If the color TV of the IC is used to continuously damage the switch tube, and the absorption circuits V901, R904, R905, and C911 are not abnormal, check the R918 of the 2 pin and the start resistor R920 (easy to be bad). The poor performance of the N901 is one of the important reasons, and the replacement must be genuine. If it is a thunderstorm season, it is best to replace the N902 optocoupler. Lightning striker optocoupler is easily damaged. If a good optocoupler is not used, the voltage rise will damage other originals.
The above special cases of maintenance are just a matter of throwing bricks. The cases referred to have my own actual maintenance experience, and also refer to the maintenance process of netizens from other websites. I would like to express my gratitude. I often see netizens asking about circuit drawings in the forum, and not the original version of the machine, otherwise there is no way to start. In fact, the masters who have a lot of skills are not stuck in these situations. No matter how the circuit changes, there will be certain rules to follow. The most typical ones are the switching circuit and the scanning circuit. When we have time, we can find out that the related circuits are at least 60%-80% similar to the gods. The difference is also certain. Let us look at my back. The uploaded drawings are believed to have a feeling. These nine drawings can find its shadow on at least 20 boards, or not. Therefore, if there are netizens who need drawings in the forum, I sometimes give him only similar drawings for reference.
As a maintenance person, we must constantly consolidate our theoretical knowledge, and we must be able to adapt to the ever-changing technological needs. I have been doing maintenance for fifteen years, and I have seen a variety of boards and circuit diagrams, and gradually have the feeling of growing together. Any circuit, in the final analysis, is nothing more than a combination of basic circuits such as amplifying circuits, switching circuits, oscillating circuits, IC control circuits, etc., nothing to be fussed. Therefore, I believe that if we want to achieve a hundred poisons, we must have solid basic skills, and we must completely abandon the money-based learning method. Don’t think that this board is too old to make money and despise it. Without studying it, we are just losing the most precious things, because such a board is best for practicing our basic skills. If everything is the starting point for learning to make money, then don’t want to make achievements in your life.
You can also look at the article "Take the Dragon" by the netizen [Kangjia HD color TV P2902T burning tube himself repair method], this is a very good post worth learning.
Also attached to Konka P2902T HD color TV drawing PDF (applicable models: P2908T, P3460T, P3409T, P2903T, P3618T, P2906T, etc.) Konka 1.pdf
Konka 2.pdf
Konka 3.pdf
Konka 4.pdf
Konka 5.pdf
Konka 6.pdf
Konka 7.pdf
Konka 8.pdf
Konka 9.pdf
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