The repair of quad output switching power supply
can be divided into two steps:
1. After a power failure, "see, smell, ask, measure".
1.1 See: open the shell of the power supply, check whether the fuse fuses, and then observe the internal situation of the power supply. If the scorch or component rupture are found on the PCB board of power supply, we should focus on the components here and related circuit components.
1.2. Smell: smell the power inside whether there is a paste, check whether there are burnt components.
1.3 Ask: ask the process of power damage, whether to operate the power supply violations.
1.4 Amount: under the condition of no power, use a multimeter to measure the voltage at both ends of the high voltage capacitor first. If the switching power supply fails to vibrate or the switching tube is open, in most cases, the voltage at both ends of the high-voltage filter capacitor is not discharged. This voltage is over 300 volts, so please be careful. Use a multimeter to measure the positive and negative resistance at both ends of the AC power line and the charging condition of the capacitor. The resistance value should not be too low, otherwise, there may be a short circuit inside the power supply. The capacitor should be able to charge and discharge. Off the load, respectively measure each group of output to the ground resistance. Normally, the needle should be capacitor charge and discharge oscillation, and the final indication should be the resistance of the circuit of the discharge resistance.
2. The power detection
After power on, observe whether the power supply has burning safety and smoke phenomenon of individual components. 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 voltage output, focus on rectifying diode and filter capacitor.
Measure whether there is an output of secondary coil of a high-frequency transformer. If there is no output, check whether the switch tube is damaged, whether there is vibration, whether the protection circuit is in operation, etc. If there is, check the rectifier diode, filter capacitor and three-way stabilizer tube on each output side.
If the power supply
starts and stops at once, the power supply is in the protection state, and the voltage of the PWM chip's protection input pin can be directly measured. If the voltage exceeds the specified value, it indicates that the power supply is in the protection state, and the reason for protection should be emphatically checked.