The fault of the lines, including the power cord is damaged and not energized, the contact port is oxidized and the contact is poor. One shall focus on checking whether the input line and output line are energized. If the line of the China power adapter is faulty, it can be solved by replacing the power cord.
1. Switching power supply load short-circuit failure (especially DC/DC converter short-circuit or poor performance and so on). At this time, first disconnect all loads of the switching power supply circuit and check whether the switching power supply circuit is faulty or the load circuit is faulty. If the load circuit is disconnected and the voltage output is normal, it means that the load is too heavy. If it is still abnormal, it means that the switching power supply circuit is faulty.
2. The failure of the filter capacitor or rectifier diode at the output voltage end of the power adapter can be judged by the replacement method.
3. The function of the switch tube is reduced, causing the switch tube to fail to conduct normally, which will increase the internal resistance of the power supply and decrease the load capacity.
4. Poor switching transformer not only causes the output voltage to drop, but also causes insufficient excitation of the switching tube, thus damaging the switching tube. The 5300V filter capacitor is bad, causing the power adapter's power supply with poor load capacity, and the output voltage will drop as soon as the load is connected.
Excessive output voltage generally comes from voltage stabilization sampling and voltage stabilization control circuits. In the closed control loop composed of DC output, sampling resistor, error sampling amplifier such as TL431, optocoupler, power control chip and other circuits, any one of the components will cause the output voltage to rise.
The fuse is normal and no output voltage indicates that the switching power supply is not working or has entered a protection state. The first step is to check the value of the startup voltage of the startup pin of the power control chip. If there is no startup voltage or the startup voltage is too low, check whether the external components of the startup pin and the startup resistor are leaking. If the power control chip of the power adapter is normal, the fault can be quickly found through the above monitoring.
If there is a starting voltage, measure whether there are high and low level jumps at the output terminal of the control chip at the moment of power-on. If there is no jump, it means that the control chip is damaged, the peripheral oscillation circuit components are damaged, or the protection circuit is faulty. Check one by one by replacing the control chip and checking the peripheral components; if it is changing, the switch tube is bad or damaged in most cases.
Mainly check the rectifier bridge, each diode, switch tube and the large filter capacitor on 300 volts and other parts. If the fuse turns black, it may also be caused by a problem with the anti-interference circuit.
Special attention should be paid to the fact that the fuse is burnt due to the breakdown of the switch tube, which usually burns the power control chip and the current detection resistor. The thermistor is also easy to burn out along with the fuse.
These are the common faults and maintenance of power adapters. In addition, we must pay attention to the daily maintenance of power adapters, which can reduce the occurrence of failures and effectively extend the service life.