1、 Line fault
Line fault, including power line damage, no power, contact oxidation, poor contact and so on. Key inspection
Check whether the input line and output line are powered on.
If there is a line fault, it can be solved by replacing the power line.
2、 The output voltage is too low
The following are the main causes of low output voltage:
Two point one
In case of load short-circuit fault of switching power supply (especially DC / DC converter short-circuit or poor performance, etc.), firstly 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; or if it is still abnormal, it indicates that the switch power supply circuit is faulty.
Two point two
The failure of filter capacitor or rectifier diode at output voltage end can be judged by replacement method.
Two point three
The performance of the switch tube decreases, which leads to the failure of normal conduction of the switch tube, which increases the internal resistance of the power supply and reduces the load capacity.
Two point four
The bad switch transformer not only causes the output voltage to drop, but also causes the switch tube excitation insufficient to damage the switch tube
2.5 the 300V filter capacitor is poor, resulting in poor load carrying capacity of the power supply, and the output voltage will drop as soon as the load is connected. 3、 Output voltage too high
The high output voltage usually comes from voltage stabilizing sampling and voltage stabilizing control circuit. In the closed control loop composed of DC output, sampling resistance, error sampling amplifier such as TL431, optocoupler, power control chip and so on, the output voltage will rise if any part fails.
4、 The safety tube is normal and there is no output voltage
The safety tube is normal and no output voltage indicates that the switching power supply is not working or has entered the protection state.
The first step is to check the starting voltage value of the power control chip's starting pin. If there is no starting voltage or the starting voltage is too low, check whether the external components and starting resistance of the starting pin are leaking.
If the power control chip is normal, the fault can be quickly found by the above monitoring. If there is start-up voltage, measure whether there is high-level and low-level jump at the output end of the control chip at the moment of startup. If there is no jump, it indicates that the control chip is damaged, the peripheral oscillation circuit components are damaged or the protection circuit is faulty. By replacing the control chip and checking the peripheral components, check one by one; if the jump occurs, most of the time it is the switch tube is defective or damaged.
5、 The insurance is burnt out or blown out
Mainly check the rectifier bridge, diodes, switch tubes and large filter capacitor on 300 v. Cause fuse burning, blackening, may also be caused by anti-interference circuit problems. It is particularly noteworthy that the fuse is burned due to the breakdown of the switch tube, which usually burns out the power control chip and the current detection resistance. Thermistors can easily burn out together with the fuse.