Changhong color TV PF2139 repeated burning insurance confusion - android - Phones Developers

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A Changhong PF2139 color TV of a friend often burns 3.15A insurance at the moment of booting. Once it can be turned on, it can be watched normally. It lasted for nearly one year. After several masters repaired, it could not completely eliminate the fault. The fault of burning insurance from time to time still exists; He played with him one day and told me about his distress. Because he didn’t bring the tools at the time, he brought the TV back when he came back...
Idle the boot, observe the more common A3 power supply, I think the problem should not be big, why not repaired by many people! Look carefully that the insurance has been blown, but it is not like a serious over-current black, but there is some white smoke on the glass tube wall, and the insurance is naturally blown. Is the quality of the insurance problem or some of the power supply components are faulty, did not dare to draw conclusions, and then flipped out the circuit board, found that the power supply has been unrecognizable, it seems that the former masters have worked hard on the power supply. The power supply has no obvious short-circuit components. The test is installed on 3.15A, and the insurance is broken. The power is off the C pole, the degaussing coil is removed, and the fuse is turned on or off. Then remove the three-end degaussing resistor, measure the four diodes without short circuit, use a 2A ordinary insurance to go up or burn... At this time, the suspected object only has 400V filter capacitor. Remove the capacitor to measure the charge and discharge. See 470uF/ 450v (should be replaced by the former master), try to install a 100uF/400v filter capacitor, power on the measured capacitance at both ends 300v normal, restore the circuit, boot display blue screen is normal. . .
Putting the removed 470uF/450v electrolysis on a 29-inch color power supply to work normally, there is no problem in repeatedly switching the machine, indicating that the 21-inch machine is equipped with a large-capacity filter capacitor. . Analysis of the reason, the larger the capacity of the filter capacitor, the greater the initial charge current during cold start, the excessive charge current will fuse the fuse, if the insurance is increased, the large current will impact the bridge rectifier circuit, which is not worth the loss. Therefore, the power supply filter capacitor is not as large as possible, it is suitable!