Last night, my apprentice called me and said, "Brother, have you eaten?" (He never used to call me "Master," saying he wanted to be more familiar. I just let it go. 😊) I replied, "Eaten? What do you mean?" He continued, "My uncle's TV is broken. It’s been repaired a few times but still doesn’t work well. He asked you to come over tonight to fix it for him." I agreed to meet at 9 PM. The problem was that the color TV in his uncle's house would shut down automatically. Sometimes it would turn on by itself again, and other times it wouldn’t turn off for hours. Most of the time, it would shut down after two or three hours. The apprentice went to the house first. He took apart the power supply tube and tested everything. After some repairs and re-soldering, it seemed okay. But the next day, his uncle called and said the problem was still there. Friends of mine know that soft faults in home appliances are really frustrating. The user's device breaks, and after sitting for an hour or two, it works fine again. Then they leave, and the fault comes back later. Time is money, and who has the patience to wait for hours at a customer's home? The second time, the apprentice took the board back to the shop. He even called me for advice. I told him to check for random shutdowns. If the standby light wasn't on, the issue was definitely in the power circuit. The power circuit usually involves a few components—starting capacitors, resistors, standby transistors, optocouplers, etc. I advised him to replace any faulty parts. He followed my instructions and tested the machine for over ten hours. When he returned, he confidently claimed, "This time, it's definitely fixed. I've tested it for over ten hours without any issues." But the next day, he got a cold shower—his uncle called again, saying the TV was still broken. "Your kid is blowing big!" The apprentice was confused and upset. How could it work in the shop but not at home? It felt like being a second wife's monk—no one could figure it out. At 9 PM, I finally went to the house. It was a 29-inch Skyworth rear-projection TV. Although Skyworth isn't the best brand, their color and sound quality were top-notch compared to others. I asked the apprentice to disassemble and check the unit. Considering he had already tested it for over ten hours, I thought there were no hidden issues. The only thing we hadn’t checked was the power switch. I asked him to remove the panel switch and measure the resistance with an ohm meter. One set of contacts showed about 4.7 ohms, while the other was around 50 ohms and unstable. No need to think further—he needed to replace the original power switch. After replacing it, the TV worked perfectly. His uncle was happy and invited me to stay for dinner. We had beer, seafood, and hot pot. It felt like a celebration. Later, he even paid for two boxes of beer. As the night grew late, the TV kept running, and everyone was enjoying themselves. His uncle said, "Let me learn from your master." The autumn air was cool, and the evening was refreshing. Everyone left happy, drinking and going home. **Summary:** The power switch is the most frequently used component. After repeated on/off cycles, especially with low-quality domestic parts, the internal contacts can develop an oxide layer due to sparks. Over time, carbon deposits build up, causing poor contact. When enough current passes through, the oxide heats up, increasing resistance and cutting off the current. This leads to random automatic shutdowns. Once cooled, the resistance drops, and the TV may turn on again. That's why checking the power switch is crucial. It’s based on years of experience. I hope this small tip helps you in the future! Thanks for reading!
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