Power supply repair technique
The maintenance of switching power supply can be divided into two steps:
In the case of power failure, "look, smell, ask and measure"
Look: Open the shell of the power supply, check whether the fuse is blown, and then observe the internal situation of the power supply. If the PCB of the power supply is found to be burnt or the components are broken, the components and related circuit components here should be inspected emphatically. asset management
Smell: Smell the inside of the power supply for burnt components.
Q: Ask about the damage to the power supply, and whether it is illegal to operate the power supply.
Measurement: Before the power is turned on, use a multimeter to measure the voltage at both ends of the high-voltage capacitor. If the switching power supply does not vibrate or the switch tube is open, in most cases, the voltage at both ends of the high-voltage filter capacitor has not been released, which is more than 300 volts, so be careful. Use a multimeter to measure the forward and reverse resistances at both ends of the AC power line and the charging of the capacitor. The resistance value should not be too low, otherwise there may be a short circuit inside the power supply. Capacitors should be able to charge and discharge. Disengage the load, and measure the grounding resistance of each group of output terminals respectively. Under normal conditions, the watch hand should swing with the capacitor charging and discharging, and the last indication should be the resistance of the discharge resistance of this circuit.
Power-on detection
After electrifying, observe whether the power supply has burning safety and smoking of individual components, and if so, cut off the power supply in time for maintenance.
Measure whether there is 300-volt output at both ends of the high-voltage filter capacitor. If there is no output, check the rectifier diode and filter capacitor.
Measure whether the secondary coil of high-frequency transformer has output. If not, check whether the switch tube is damaged, whether it vibrates, whether the protection circuit operates, etc. If yes, check the rectifier diode, filter capacitor and three-way voltage regulator on each output side.
If the power supply is started and then stopped, 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 reasons for the protection should be mainly checked.
