Skyworth color TV 25T91AA lightning strike three faultless maintenance examples - Appliances

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Fault phenomenon: Skyworth color TV model 25T91AA was struck by lightning and no. 3 failed to work. Repair process: I first checked the fuse and found it blown. Then I discovered that Q604 had also been damaged. While repairing, I tested the switching power supply output for each group and didn’t find any short circuits. Given the lightning strike, I usually try to use a module to check if the cold parts of the TV are damaged. After replacing Q604, I connected the module, adjusted the voltage to 125V, and the voltages on all channels were basically normal. However, pressing the P+ button didn't turn the TV on. Even when I shorted the P+ pin, it still wouldn't start, likely due to the child lock function. If the user had enabled the child lock, the P+ button wouldn't work, so I wasn't sure if the problem was with the CPU1. Without a remote control, I tried using a universal remote. I noticed that some models can be turned on by pressing the volume button after pressing the settings button on the universal remote while the TV is in standby. But even with that, the TV still wouldn’t turn on. I then decided to remove the memory chip to test. When the OM8370 is without memory, it boots into a limited state. I had done this before (not sure if all models behave the same), but even after removing the memory, the TV still wouldn’t start. I had to inform the user that the main chip might be faulty and suggested bringing it in next week. When the new chip arrived, I removed the old OM8370, installed a socket, and replaced it with a new one. The TV turned on, the picture looked normal, but the characters were shifted upward. Since there was no memory installed at the time, I tried a second chip, which also failed to boot. Finally, the third chip worked. I used the universal remote, and all functions were normal. I connected the video cable, and both the image and sound were fine. I re-soldered the memory and tested the TV again. It went into standby, and when I pressed the power button on the remote, it still wouldn’t turn on. Was the remote faulty? I removed the memory again, and the screen came back. I tried the AV/TV button, and the signal switched properly. The volume was also working. Pressing the power button on the remote could turn it off, but not on. I checked the voltages on each pin of the chip, and they were all normal. No clear clues for further repairs. Could it be that the first chip was just bad? I tried replacing it again, but it still didn’t work. Both chips had the same failure probability, and they both worked during the boot-up phase. At this point, I started doubting the power supply again. I adjusted the voltage to 125V, but maybe it was too low? I tested it at 135V with the module, and everything worked perfectly. Re-testing the original chip and the one I had previously deemed "dead" showed that they were actually functional. After checking the power supply, only the fuse, Q603, and Q604 were damaged. Once replaced, the TV returned to normal operation. This repair took a long detour, but it confirmed my previous theory about the sensitivity of the OM8370 to the power supply. I remember that the newly repaired OM8370 is very sensitive to power input.