My relatives have a Haier 29F7A-PN TV with no sound. Now it has been replaced with LCD TV. The fault TV has been placed for more than a year. Although it is not a professional maintenance, it can be a hobby, like drumsticks, and it’s nothing to do. Opportunity to practice handcuffs. Relatives said: The old TV throws a pity, it is worthless to sell, you will die as a living horse doctor. Ok. Anti-Blue Light Hydrogel Screen Protector
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1, first look for drawings from the Internet to download the title of Haier 29F7A-PN circuit diagram and the physical board does not match at all, no drawings å’‹ operation, had to look at it, almost Haier 29-inch maps have been downloaded, a few days down It is hard to find a very similar Haier D29FV6H-PR drawing, (several models are this drawing), although not exactly the same, but the overall basic is the same, it is not easy. No wonder some netizens said that Haier color TV is the original one.
2, troubleshooting troubleshooting power supply 300v is 280v, switching transformer secondary + B132v is 120v, the remaining 10v, 15v, 16v, 30v power supply is slightly lower, but basically normal. Since there is no high voltage output, the scanning circuit is checked. Field block LA78041 internal short circuit, rectifier tube AU3A breakdown, current limiting resistor 1 ohm R642 open circuit. After the above originals are replaced, the high voltage is there, the screen has a snowflake point, but the upper half has a black screen of 10 cm and is unstable. The viewing 180v is 165v, and after half an hour, all black screens, no high voltage. There is a slight slamming sound in the line tube. If the measurement is removed, there is no problem. It is also fired and carefully checked. It turns out that the insulating plastic sheet between the tube and the heat sink has a click-through and is not tightly fixed. The nut is no longer ignited and has high pressure. But it can only be started twice, and sometimes it can start sometimes and sometimes it can't start. Later, it can't be started twice. Check that the push tube has no base voltage, and then the output of the 26 feet of STV9118 should be 2 volts, now 11 volts. Normal, replace STV9118, the fault remains. Check that the digital board and the LM1269 do not have a 5 volt supply, and then find that the Q570 does not have a 5 volt output. The figure is marked with a small power amplifier transistor, which is actually a three-terminal regulator 7805, 7805 is fixed on the heat sink. After loosening the screw, it is found that all three feet are desoldered, and the second boot can be turned on after the repair, but it is still black. Looking at the board again, I found that there was a small crack on the surface of LM1269 DNA. The electronics store didn't sell LM1269 DNA, and replaced it with LM1269NA. The screen was successfully turned on, but the color was reddish. Entering the bus adjustment, basically normal, but not received. Some people say that NA can't replace DNA, and some say yes. The owner of the electronic mall said that it was still good to use the original, so I bought LM1269DNA on Taobao. After loading it with joy, the normal display of the full screen snowflake only lasted for 15 seconds and the black screen was intermittent. It was completely black. Check the 22-pin ABL circuit of LM1269DNA. For 4.7 volts, now 1.4 volts, check the ABL circuit components one by one, no problem, or suspect LM1269DNA, bought a piece at that time, had to change to LM1269NA again, ABL voltage restored to 4.4 volts can start, but the screen color is still reddish, Also suspected that there is a problem with the digital board, there are two digital boards on the motherboard.
A board
B board
There are two integrated blocks of M61266 and M37160 on the A board. The PW1233 and MST9886 integrated blocks on the B board and the M61266 on the A board convert the analog signal into a digital signal and send it to the B board PW1233 for line-by-line processing. The processed signal is from PW1233. The output is sent to the video processing circuit LM1269DNA, and finally the RGB three primary color signals are output from the LM1269 DNA, and sent to the tailgate LM2429 for video amplification. That is to say, the source of RGB is output by pins 14, 15, and 16 of M61266, and the measured voltage should be 2.5v. The actual 3 feet are only 1.5v on average. The other feet also did not match the data on the Internet, so I decided to replace the M61266. I bought M61266 and LM1269DNA from the Internet. Since there are no hot air guns with two 30-watt soldering irons at the same time, I have to remove the M61266 and re-weld the new ones. The LM1269DNA was replaced, and the display was basically normal after power-on, re-entering the bus fine-tuning. There is no problem with the boot, I thought about repairing it, but the next day the boot screen will light up and the black screen, the voltage detection of each channel is normal, and suddenly the tube tube filament is not bright. Check the wire solder joint crack on the main board to the tailgate filament voltage.
It may be repeated soldering the motherboard toss. After welding, it is too low to detect the AC voltage of the filament, which should be above 4 volts. The screen is sometimes dark and unstable. The filament voltage is provided by the high voltage package, and the other voltage outputs are normal. It is not worthwhile to change the voltage of the filament to change the voltage of the filament. The method on the Internet is to disconnect the original circuit and use a thin insulated wire to wrap around the coil circuit on the high voltage package for three turns. The boot screen is normal, the filament voltage is 3.9 volts, and there are no problems for a few days, all ok.
3 Feelings: 1. Hobbies, no previous contact, you must learn, have patience, not afraid of trouble, find more relevant information. 2, to dare to toss, but also to be good at brains, no idea to put down first, there are ideas to do it again, do not toss and do not give up. 3, online masters, their experience is very valuable, is the basis for amateurs to learn and progress, TV can be repaired first thank you heroes.