Recently, I repaired a Changhong 2916 color TV. After checking, the problem was a blown tube. I removed the line tube and tested the main power supply voltage, which was 115V and normal. All other voltages were also within range. There was no short circuit in the wiring, and the components on the board appeared fine. The downstream reverse capacitance was sufficient. I replaced the line feed tube C2253N, and everything worked normally. The user took the TV home, but after four hours, they called back saying it had broken again. When I went to check, the tube was burned out. I suspected there might be some hidden issues that I missed.
The user mentioned that the TV had been repaired before by another technician, and it only lasted three hours before burning out. Since the previous repairer couldn’t afford to fix it again, the user came to me for help. It felt like a tricky situation. I carefully checked the board for any soldering issues and re-soldered any loose connections for safety. Then I replaced the tube again and observed the performance. Initially, everything looked good, but after about half an hour, I noticed the heat sink was extremely hot. I estimated that the tube might fail after that time. I wondered if the issue was due to insufficient drive.
I then checked the primary power supply of the line transformer, and it was normal. The resistance R404 (5.6K) was okay, and the filter capacitor C405 (250V 10μF) was tested off the board and showed no capacity. After replacing it and testing the machine again, I found that after half an hour, the tube didn’t get as hot. I ran the TV for four hours without any issues. The user has been using it for six days now, and there’s been no fault so far. It seems like the problem was resolved, but I still keep an eye on it just in case.
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