How to repair 12V power adapter

Nowadays, the development of science and technology is more and more rapid, but no matter how the technology develops, it depends on the power source. There are many kinds of power sources, such as solar batteries, lithium batteries, and mobile batteries, but the power adapters corresponding to different batteries are also different. The same, but the most common is the 12v power adapter. The 12v power adapter is also very prone to errors. But for 12v power adapter repair and what are the faults of 12v power adapter. The following editor of switching power supply manufacturers will share with you in detail.

12V power adapter, pull the plug into the power socket, no sparks, indicating that the primary circuit has failed. Open the power supply shell, the power supply works well.

Carefully observe the components, there are no burn marks, and there are no signs of overheating and yellowing on the back of the circuit board. Use a multimeter to measure the power input terminal, stop infinity, the pointer does not respond.

Pay attention to check the current-limiting resistor, fuse and rectifier diode. It is found that the fuse is blown, and it is judged that there may be a short-circuit fault in the circuit. Online measurement of the rectifier filter capacitor, there is no charging response, no response to the test of the meter pen, and the pointer indicates the resistance is about 100k.

The filter capacitor is welded and measured with a multimeter in 1K mode. There is no charging reaction. The resistance value is 30k. Reverse measurement. It is still a 30k resistance and there is no charging reaction. Carefully observe that there is a trace of leakage on the capacitor’s negative electrode. Then re-measure the input power input terminal, the resistance is about 1 megohm, the input resistance is normal.

 indicates that the power failure should be caused by the breakdown and leakage of the filter capacitor. Because there is no 400v10u filter capacitor on hand, and there is still a place for a filter capacitor on the circuit board, two capacitors 400v3.9u and 400v6.8u are used in parallel to connect to the circuit. Solder the fuse, measure the input end of the power supply at the 1K range of the multimeter, and the resistance is 1 MΩ, indicating that the circuit has returned to normal.

Measure the output diode of the secondary power supply, and there is no sign of damage. Power on, the indicator light is on. No-load measurement output voltage, 13v, in the normal range. Connect the 20Ω slip wire rheostat into the circuit, adjust the resistance, keep the current at 2A, and power on for 30 minutes without any failure. Put the circuit board into the shell, continue to power on for 30 minutes, the shell is warm.

Because the adapter is used for monitoring equipment, 24 hours X 365 days use, it is estimated that the power adapter has been working for a long time because of poor heat dissipation of the power supply and the capacitor overheats and leaks. For insurance, 30 small holes were drilled with a 1MM drill bit on the side of the low-voltage part of the adapter shell to facilitate heat dissipation. At this point, the repair is complete.