Hisense LCD TV TLM42V68PA flower screen fault repair example - appliance repair - Huaqiang electronic network

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Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

A Hisense LCD TV TLM42V68PA flower screen fault repair. At the beginning of the boot, the English-speaking English icon is basically clear, and the image is out of the picture. My first feeling is that the screen is bad or the logic board is bad. Start the test logic board five voltages. The 12V power supply is stable. VGL-5.6V VDD3.3VVDA14VVCOM5.6V is basically normal. Only VGH18 fluctuates severely. Suspected that there is a problem with the logic board, the VGH voltage of the two flexible cables removed to the screen fluctuates. Logic board power control chip TPS65161 mobile phone found the function pin 10 pin voltage is 10V or so measured only 2V or so far difference, I want to buy chip repair afraid of other problems anyway, the board is not expensive. Order this logic board number V420H1-C12 (Chi Mei screen) online and arrive in a few days. I tried it in the store (I have this kind of screen line with the universal board). The VGH voltage is still only about 18V. I thought it was bad. Ask the seller how much the voltage is. It is not clear according to the experience. VGH voltage should be 24V. about. Going to the machine test is really the same as before, the measured 18V fluctuations and more trials sometimes only 12V, only the suspect board has a problem immediately. In a few days, the goods are still in the store and try to be the same as the previous one. I don’t think it’s so bad. It’s the same as the user’s home test. It’s still serious. Sometimes the gray screen does not work. Several sets of voltages are gone without VDD. There is no bottom in the heart and the user said that it is possible that the screen is broken and it is a bit troublesome to take it back. The user agrees to pull back and use the universal board to check the logic board. Surprise appeared on the screen and the video was displayed in the upper right corner of the blue background. It’s a motherboard problem. I was not convinced by the two conditions that I did not expect the motherboard problem. It is the VGH voltage. According to experience, there is a logic board with five voltages around 24V that will not be affected by the motherboard (because the screen power supply and the logic board should be normal 5 voltages should be normal). Ok, fix the motherboard now. The materials that I want to change the universal board are all ready-made. I think that the replacement of the board can't improve the technology. It can't be replaced with a universal board. Check the motherboard 1.2V2.5V3.3V are normal, the main chip is not overheated, but also measured by the oscilloscope 27M crystal shock is normal. Also checked the main chip to flash memory exclusion did not find the problem. Finally, it is found that the voltage of the LVDS output port is abnormally normal and should be about 1.2V. As a result, it is found that there are several groups with fluctuations of only about 0.6V. It seems that the problem is here. What causes the voltage to be low? The LVDS driver power supply 1.2V is normal. The chip terminal is also normal. This low voltage will cause all voltages to be low. The LVDS cable LVDS cable double-color line end to the ground resistance voltage is low, the resistance of the group is also very small, only 1K less than the normal fluctuation of the 4K or so. There are no parts from the main chip to the upper screen cable port. The maximum problem may be directly related to the main chip MT8222ARSU. Two pieces were set online. I am ready to change the delivery today. Remove the motherboard and measure the resistance of the main chip power supply to the ground to compare the short circuit of the welding. When I soldered the main chip, I measured the resistance of the groups with low output voltage is still low. There are no other parts between the strange LVDS output and the main chip. Finally remove the output strip. The problem was finally found. There are a lot of dirty things under the plastic seat and I can't tell what it is. After the final cleaning, the original master chip was welded back to the test machine and finally the normal image was obtained. After changing the phone, the picture can't be sent up. Why is it too much to compress the picture?