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

Probe domestic switch needle KG-300K, needle head diameter is 3.0mm, normally open switch needle

MOS power IC full range

Shunluo high frequency inductor, parallel stack inductor, shun winding inductor, authorized agent

1.5PF SOT23-6 Low Capacitance 5V Breakdown Voltage 6V SRV05

L0504-Murata muRATA common mode inductor 90Ω 150mA

Fault phenomenon: Skyworth color TV 25T91AA after a lightning strike, the TV won't turn on. Repair process: I started by checking the fuse and found it blown. Then I checked Q604 and found it also damaged. While repairing, I tested each group of the switching power supply and found no short circuits. As this was a lightning strike, I usually use a module to check if any cold components were damaged. After replacing Q604, I connected the module, adjusted the voltage to 125V, and all output voltages appeared normal. However, pressing the P+ button didn’t turn on the TV. Even shorting P+ didn’t work, but I realized that Skyworth TVs have a child lock function. If the user had enabled it, the P+ button wouldn’t work. So I wasn’t sure if there was an issue with CPU1. Without a remote control, I tried a universal remote. When the TV was in standby, pressing the setting button followed by the volume button on the universal remote sometimes worked. But even after trying this, the TV still wouldn’t turn on. I considered removing the memory chip to test. Since the OM8370 boots in a boot state without memory, I had done this before (not sure if all models behave the same). After removing the memory, the TV still wouldn’t start. I told the user the super chip might be faulty and suggested bringing it in next week. Once the new chip arrived, I replaced the OM8370, installed a socket, and put in a new one. The TV turned on, the raster was normal, but the characters were shifted upwards. At that time, there was no memory installed. I had bought three chips; the second one didn’t work, but the third did. With the universal remote, all functions worked normally. I plugged in the video cable, and both image and sound were fine. I re-soldered the memory and tested again. The TV was in standby, but pressing the power button on the remote still didn’t work. Was the remote faulty? I removed the memory again, and the raster returned. Trying the AV/TV button on the remote allowed me to switch inputs, and the volume worked. Pressing the power button turned the TV off, but not on. I checked the voltage of each pin on the chip, and they all looked normal. No clues for further repair. Could the first chip be good? I tried the original one again, but it still failed. The two chips should have had similar chances of failure, and they worked during boot. At this point, I rethought the power supply. I adjusted the voltage to 125V, but maybe it was too low. I tried 135V instead, and everything worked. Re-testing the original chip and the one I had previously dismissed showed no improvement. After checking the power supply, only the fuse and Q603/Q604 were damaged. After replacing them, the TV worked normally. This case made me take a detour, but it confirmed my previous theory about the sensitivity of the circuit to voltage, especially regarding the OM8370’s power supply requirements. It reminded me how crucial stable power is when working with such sensitive chips.