Changhong color TV 2961 repeated burning tube fault repair example - Home Appliances

Filter 18.432M

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

A few days ago, I repaired a Changhong 2916 color TV. After investigation, the tube was broken down. Take off the line tube and measure that the main power supply voltage is 115v normal. The other groups of voltages are also normal. There is no short circuit in the check line, and there is no abnormality in the circuit board parts. The downstream reverse capacitance is enough. Then the line feed tube C2253N, the picture sound is normal, for the user to use. Four hours after the TV was taken away, the user called and said it was broken. I went to see it, and it was burned out after the investigation. I think there are probably hidden dangers that have not been detected. At this time, the user said that this TV has also changed the line of management before. It just burned after watching it for 3 hours. Because the master of the TV repair had no money, I was embarrassed to call again, so I asked for repair. It seems that there is an addiction. Carefully check the circuit board parts for no solder joints. For safety reasons, re-weld loose parts. Then change the tube to observe. The image did not find any abnormality. After half an hour, the hand touched the tube heat sink, which was especially hot. It is estimated that the tube will be sacrificed after half an hour. I wonder if it is caused by insufficient promotion? So check the line to promote the primary power supply of the transformer, normal, primary power supply resistance R404, 5.6K normal, primary power supply filter capacitor C405, 250V10U, take off the test has no capacity, after the test machine, half an hour after the hand touch pipe, not special heat. Retest the machine for 4 hours, no abnormality, and the user has used it for 6 days, and no fault occurs.