source:Industry News Popular:adapter release time:2022-04-25 11:37:50 Article author:yu
1. In the case of power failure, "look, smell, ask, and cut"
First of all, before the switching power supply is not powered on, use a multimeter to measure the voltage across the high-voltage capacitor. If the fault is caused by the failure of the switching power supply or the open circuit of the switching tube, in most cases, the voltage across the high-voltage filter capacitor has not been discharged, and this voltage is more than 300 volts. You leave unforgettable memories!
Since the maintenance power supply needs to be exposed to 220V high-voltage electricity, once the human body touches the voltage above 36V, it will be life-threatening. Therefore, under possible conditions, try to check whether there is any obvious short circuit or component damage in the power-off state. First, open the shell of the power supply, check whether the fuse is blown, and then observe the internal situation of the power supply. If you find that the components on the PCB board of the power supply are broken, you should focus on checking this component. Generally speaking, this is the main reason for the failure; smell the power supply Check if there is a smell of paste inside, check if there are burnt components; ask about the damage to the power supply and whether there is any illegal operation on the power supply, which is necessary for repairing any equipment. After the initial inspection, a more in-depth inspection of the power supply is required.
Use a multimeter to measure the forward and reverse resistance at both ends of the AC power cord and the charging condition of the capacitor. If the resistance value is too low, it means that there is a short circuit inside the power supply. Under normal conditions, the resistance value should reach more than 100 kiloohms; the capacitor should be able to charge and discharge, if damaged , it is shown that the resistance at both ends of the AC power line is low and is in a short-circuit state, otherwise the switch tube may be broken down. Then check that the DC output part is disconnected from the load, and measure the resistance to ground of each group of output terminals. When it is normal, the needle should have a capacitor charge and discharge swing, and the last indication should be the resistance value of the bleeder resistor of this circuit. Otherwise, most of them are caused by reverse breakdown of the rectifier diode.
2. Power-on detection
After passing the above tests, the power-on test can be performed. At this time is the key, need to have certain experience, electronic foundation and maintenance skills. Generally speaking, you should focus on checking the input end of the power supply, the switching transistor, the power supply protection circuit, and the output voltage and current of the power supply. If the power supply starts and then stops, the power supply is in the protection state, and the voltage of the protection input pin of the PWM chip can be directly measured. If the voltage exceeds the specified value, it means that the power supply is in the protection state, and the reason for the protection should be checked. Due to exposure to high voltage, it is recommended that friends without electronic foundation need to operate carefully.
3. Common faults
3.1. Fuse blown
Generally, a blown fuse indicates a problem with the internal wiring of the power supply. Since the power supply works under the condition of high voltage and high current, the fluctuation and surge of the grid voltage will cause the current in the power supply to increase instantaneously and cause the fuse to blow. The key point should be to check the rectifier diodes, high-voltage filter electrolytic capacitors, inverter power switch tubes, etc. at the power input end, and check whether these components have breakdown, open circuit, damage, etc. If the fuse is indeed blown, you should first check the various components on the circuit board to see if the surface of these components is burnt and whether there is electrolyte overflow. If the above situation is not found, use a multimeter to measure whether the switch tube has a breakdown short circuit.
3.2. No DC voltage output or unstable voltage output
If the fuse is intact, there is no output of DC voltage at all levels under load conditions. This situation is mainly caused by the following reasons: open circuit and short circuit in the power supply, failure of the overvoltage and overcurrent protection circuits, the oscillation circuit does not work, the power supply is overloaded, and the rectifier diode in the high frequency rectifier filter circuit is broken down. Filter capacitor leakage, etc. After measuring the secondary components with a multimeter, after ruling out the breakdown of the high-frequency rectifier diode and the short-circuit of the load, if the output is zero at this time, it is certain that the control circuit of the power supply is faulty.
3.3. Poor power load capacity
Poor load capacity of the power supply is a common fault, which usually occurs in old-fashioned or long-working power supplies. Should focus on checking whether the Zener diode generates heat and leakage, the rectifier diode is damaged, the high-voltage filter capacitor is damaged, etc.
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