Konka color TV lightning fault repair example - Appliances

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Photocoupler

Due to time constraints, I had to skip the power supply section repair, which included components like the fuse, FET, and A06. After fixing the power supply, the TV showed a grating but with a black band about 5 cm wide on the left side. There were characters displayed, the buttons worked normally, but no image appeared when adding a video signal. The grating slightly shrank to the right, and a black line moved from bottom to top. I had removed the speaker during the repair and didn’t notice any sound issues. There was a persistent black band on the left. I initially thought it might be related to the line pulse, but after checking the high-voltage package at pin 10 (AFC pin) of the 76931 chip, everything seemed normal. Given that the TV was struck by lightning, the memory chip was the first to suffer. After several attempts, the data issue remained unchanged, so I concluded the main chip was faulty. I ordered three replacement chips online. A few days later, the chips arrived. I soldered in a socket, inserted the new chip, and the TV showed a grating, but the field was only about 10 cm wide, not linear. The lines looked normal, and the image appeared when a signal was added, but the new chip still had issues. Testing all three chips showed the same problem. It was unlikely all three were defective, so I considered if I had damaged them during installation. Reinserting the original chip brought back the original fault: the field was normal, but there was a black band on the left. I was stuck for a while, checked the pulse section, power supply, and other areas, but found nothing. I had no choice but to set the TV aside temporarily. Fortunately, the chips weren't expensive, so I ordered another three. After the second batch of chips arrived, the TV behaved as it did originally—showing a black band on the left, but the field was now normal. I was confused—was it that seven chips were bad? Or was it an issue with the amplitude? The fourth chip also showed some abnormalities. The process was slow, and it was already 3 AM. I decided to stop for the night and write down what I had found so far. The root cause turned out to be two capacitors, C404 and C408, which had been damaged by a lightning strike. When I replaced C404 but left C408 untouched, the first three chips worked mostly fine, though the image was slightly jittery. The next four chips showed no image or had a 3 cm black band on the left. Once both C404 and C408 were replaced, all seven chips functioned properly. Interestingly, removing C404 had little impact on the image quality. There was no pulse at pin 44 of the 76813 chip, and the symptoms matched those shown in Figure 1, though no characters were displayed. I tested this on two P21SA387 units. I purchased the first chip model 76931 H7L57L2E online. The second one, 76931 7L57L2-E, was suspected to be faulty at the time. Since C404 and C408 failed, their faults were different. After the TV was repaired, I tried the 76931 7L55N7-E chip.