Last night, the apprentice called me and said, "Brother, have you eaten?" (He never called me "Master," saying he wanted to be more familiar. I just let it slide.) I replied, "Eaten? What?" He continued, "My uncle’s TV broke down. He tried fixing it a few times but it didn’t work. He asked you to come over tonight to help me." I agreed to meet at 9 PM. The problem was that his uncle's color TV would shut off automatically. If the switch wasn't turned off, sometimes it would turn on by itself. Other times, it would stay on for hours before shutting off. It was really frustrating. The apprentice went to the house first, took apart the power supply tube, and did some repairs. After re-soldering, everything seemed okay. But the next day, his uncle called again, saying the issue remained. Friends of mine know that soft faults in household appliances are really tough. Sometimes, after a technician fixes it, the appliance works fine for an hour or two, then fails again. Time is money, and no one has the patience to sit around for hours waiting for the fault to occur. The second time, the apprentice brought the board back to the shop. He even called me for advice. I told him to check for random shutdowns. If the standby light didn't come on, the problem was definitely in the power circuit. The power circuit usually involves components like capacitors, resistors, transistors, and optocouplers. He replaced the faulty ones, and the TV worked for over ten hours in the shop. But the next day, his uncle called again—still having the same problem. The apprentice was confused and upset. How could it work so well in the shop but not at home? He was really frustrated. At the end of the call, his uncle insisted I go out to fix it himself. At 9 PM, I arrived at his uncle’s house. It was a 29-inch Skyworth rear-projection TV. Though Skyworth isn't known for the best quality, its color and sound were top-notch. I started disassembling and checking the components. Considering the apprentice had already tested it for over ten hours, I thought there were no other hidden issues. The only thing we hadn't checked was the power switch. I asked him to remove the panel switch. I used the X1 setting on the multimeter to measure the resistance between the contacts. One set was about 4.7 ohms, but the other was around 50 ohms and unstable! No need to think further—I told him to replace the original power switch from the TV. After replacing it, we tested the TV. His uncle was impressed and invited me to stay for dinner. We had beer, seafood, and hot pot, as if it were planned. He said, “You’re working too hard!†It was a great night. We talked about family, life, and even politics. Later, he paid for two boxes of beer. As I looked at the time, it was late, and the TV was still running. His uncle said, “Let me learn from your master.†The autumn night was cool and refreshing. Everyone enjoyed the evening, and I left feeling happy. In summary: Power switches are the most frequently used components. Over time, due to repeated use and poor-quality domestic parts, internal contacts can develop oxide layers and carbon deposits. This causes poor contact, increased resistance, and eventually, random shutdowns. Once cooled, the resistance drops again, which might explain why the TV turns on by itself. That’s why I suspected the power switch early on—it was a result of long-term experience. I hope this small story helps you in the future. Thanks for reading!
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