Detours, in fact, can be bypassed - Changhong color TV CHD29300 maintenance notes - Home Appliances

Apprentice overhaul process:
My first thought was that the discharge capacitor had failed! If you make that assumption, then the old guy would say, "You're wrong!" The apprentice also thought it was the capacitor, but after checking the voltage, it was 200V—normal. Then he removed the 33UF/250V capacitor for testing, and it charged and discharged fine. He lowered the accelerating voltage, and the image looked normal. He installed it back, tested it, and the fault returned. Then he adjusted the accelerating voltage again, and the image became normal once more. He suspected the high-voltage package was faulty and rushed to buy one. But when he tested it in the machine, everything worked fine. However, after replacing the casing, the TV still showed the same issue—“mountain is still the mountain, beam is still the beam.” He thought it might be a cold solder joint, so he did a large-scale re-soldering, but nothing changed. After spending over two hours trying, he had no choice but to call for help. Without hesitation, the high-voltage package was replaced, and the voltage was normal. But the back cover wasn't replaced. It felt like a challenge, and I love tackling stubborn problems like this. When he turned on the board and shook it slightly, the image became normal. No matter how hard he hit the circuit board, the TV kept working. How could the problem not occur? Without any failure, how could he even start checking? Then, Lenovo reminded him that the image became normal after 40 minutes of booting. So he decided to stop and just sit down, have a cup of tea, and chat. Unconsciously, more than an hour passed. Then the fault appeared again! He checked the green gun voltage. As soon as the test leads touched the tailgate, the user said, “Okay!” This time, my judgment was 100% correct. When he held the tailgate with his hand, the fault came back. He ordered the apprentice to replace the socket and repair the tail plate. After installation, the TV worked perfectly. Everyone was relieved and happy. Tips: Because the working current of high-definition machines is much higher than regular CRTs, and the tailstock is heavy, the quality of the existing sockets isn’t great (the machine had already upgraded the socket). Over time, due to long-term energization, the connection between the socket pin and the pin may become unstable. High-definition machines are very sensitive to such issues. If it were a regular CRT, the same poor contact in the tube holder might not be noticeable, but with HD tubes, the image changes can be misleading. Why does the machine work normally when unpacked? It’s likely because the circuit board was pulled out during unboxing, and the tailplate connection was tighter, ensuring good contact. This kind of fault is common, and experience helps. I hope this story helps you in the future. Thanks for reading!