TCL ace 2175E boot power + B voltage is too high, causing burning tube troubleshooting - News - Global IC Trade Starts Here Free Join
This TV was either good or bad. Initially, the switching power supply didn't vibrate. The user sometimes took off the TV casing and it worked fine. This time, the power was cut, and the TV didn’t respond at all. After a few attempts, it still didn’t work, so the user had no choice but to bring it to a repair shop. When they brought it back, it still didn’t function properly, and the technician said there was no fault, advising the user to take it back. Once home, it still didn’t work. That’s what the user described.
I decided to help them through an acquaintance. I thought the issue was simple—probably poor soldering. I put down my other tasks, went to their house, opened the case, and carefully checked the power supply solder joints. I found a few areas with weak soldering, though not very obvious. Since it was an acquaintance and I only charged 20 yuan, the user was very happy and even thanked me for the quick fix. They packed the TV and returned it.
The next morning, the user called again, saying the TV wasn’t responding. They mentioned a “beep†sound that was slightly different from before. Based on past experience, this sounded like a short circuit. It wasn’t as simple as I thought. I asked the user to bring it in for further testing. I wanted to save the machine and use it as a test unit.
Once inside the shop, I opened the casing and found that the power transistor was broken. To find the root cause, I disconnected the load and connected a light bulb to the power supply. The bulb lit up, but there was something unusual: the bulb was slightly brighter when the TV was turned on. I used a digital multimeter to check the startup voltage. At first, it showed around 160V, then quickly dropped to 110V, which was normal.
The breakdown of the transistor was likely due to a high starting voltage. I checked the power supply section and replaced the suspected components—voltage regulator, diode, transistor, and some capacitors. After the test, the voltage stabilized at 110V. But to be safe, I left it on for a while. After half an hour, I monitored the multimeter reading, and the voltage fluctuated between 110V and 170V, slowly returning to normal. Hmm, why was it still unstable? I double-checked the replaced parts—they were all functioning correctly.
After a careful inspection of the circuit, I noticed three small electrolytic capacitors in the power supply section. I replaced two of them, but one was hard to find. I thought about it and realized there was still an issue. That capacitor was C810, 25V 100UF. I found a 35V 100UF capacitor from an old board and replaced it. The TV worked perfectly after that. I tested it for an hour, and everything remained stable. The next day, the voltage stayed at 110V consistently. Finally, I had ruled out the problem. It felt like catching a fish! Ha ha!
(Thinking back, that capacitor must have been in good condition at the time, but I don’t know why I didn’t replace it earlier. Although the process wasn’t smooth, I finally found the core issue.)
Summary: According to the user, the TV had never been completely powered off. It was only remotely turned off. I told the user that leaving it on constantly isn’t good for the TV, as some circuits remain active and consume power. They were very obedient. If the user had shut it off properly, the tube might not have burned out this time, since the power supply would have worked normally and the output voltage would have been stable. However, the problem was inevitable. This kind of power supply has electrolytic capacitors that are prone to failure, and constant operation without shutdown caused premature aging of the components.
The first time I repaired it, I didn’t charge much. This time, to be honest and fair, I told the user the actual cost was 60 yuan. It's important to be transparent and show respect for the customer’s trust.
Zooke Connectors Co., Ltd. , https://www.zooke.com