A few days ago, I worked on a Changhong 2916 color TV. After checking, the problem was identified as a broken CRT. I removed the tube and tested the main power supply, which showed 115V — that was normal. Other voltages were also within range, and no short circuits were found in the wiring. The components on the circuit board appeared to be in good condition, and the downstream capacitors had sufficient capacitance. I replaced the line feed tube (C2253N), and the picture and sound worked fine. The user took the TV home, but after about four hours, they called back saying it had failed again.
I went back to check and found the tube had burned out. At this point, I suspected there might have been an underlying issue that wasn’t detected during the initial repair. The user mentioned that the TV had already been repaired before, and it only lasted three hours before burning out again. Since the previous technician couldn't afford to fix it properly, the user came back to me for help.
After a careful inspection, I didn’t find any cold solder joints or loose connections. For safety, I re-soldered all the joints just to be sure. Then I replaced the tube again and monitored the TV closely. Initially, everything seemed fine, but after about half an hour, I noticed the heat sink of the tube was extremely hot. I suspected the tube might fail soon after that. I wondered if the issue could be due to insufficient drive from the line driver.
I checked the primary power supply of the transformer, and it was normal. The resistance of R404 (5.6K) was okay, and the filter capacitor C405 (250V, 10μF) was tested and showed no capacity loss. When I tested the machine again, after half an hour, the tube didn’t get unusually hot. I ran the TV for four hours without any issues. The user has been using it for six days now, and so far, there have been no problems. It seems like the issue was resolved this time, but I remain cautious and will keep an eye on it in case something comes up later.
aluminum phone case,aluminum cell phone case,exclusive alloy protective case,aluminium alloy waterproof
Dongguan Yingxin Technology Co., Ltd. , https://www.dgyingxintech.com