Caution must be exercised when dealing with voltage issues to avoid life-threatening situations. Where possible, the power supply in a power-off state should first be inspected for significant short circuits or component damage. The supply voltage testing process is divided into two phases: an initial inspection and an in-depth inspection.
1. Preliminary inspection.
1.Open the power supply case, check whether the fuse is blown, and observe the inside of the power supply. If a cracked component on a printed circuit board (PCB) is found, it should be a major inspection, as this is often the main cause of failure.
2.Check the inside of the power supply for mushy smell and for burnt components.
3.Understand how the power supply was damaged and confirm whether there was a violation.
2. In-depth testing.
1.Use a multimeter to measure the forward and reverse resistance of the alternating current (AC) power cord and the capacitor charge. If the resistance value is too low, there is a short circuit inside the power supply. Under normal circumstances, the resistance value should reach more than 100 thousand ohms.
2.Check whether the capacitor is capable of charging and discharging. If it is damaged, it is manifested as a low resistance at both ends of the AC power cord and a short circuit. Otherwise, there may be a breakdown of the switch tube.
3.Check the DC output section. Disconnect the load and measure the resistance to ground at each set of outputs separately. Under normal circumstances, the gauge hand should have a capacitor charge and discharge swing, and the last indication should be the resistance value of the discharge resistance of the road. Otherwise, it is mostly caused by the reverse breakdown of the rectifier diode.
3. Power-on detection.
After passing the above checks, the power supply is tested by powering up. Focus on checking the power input terminal, switching transistor, power protection circuit and output voltage and current. If the power supply stops immediately after starting, the power supply is in a protected state. The voltage of the PWM chip protection input pins can be directly measured.
Fourth, common faults and solutions.
1.Fuse blowing: Check the rectifier diode, high-voltage filter electrolytic capacitor, inverter power switch at the input end of the power supply, etc., to confirm whether there is breakdown, open circuit, damage, etc.
2.No DC voltage output or unstable voltage output: check whether there is an open circuit or short circuit in the power supply, whether the over-voltage and over-current protection circuits are faulty, whether the oscillation circuit is working, whether the power supply load is too heavy, whether the rectifier diode in the high-frequency rectifier filter circuit is broken, whether the filter capacitor is leakage, etc.
3.Poor load capacity of power supply: check whether the components are aging, whether the switch tube is working stably, and whether the heat dissipation is carried out in time.
Example 1: A computer ATX power supply, powered on without voltage output, the power supply squeaks. After inspection, it was found that the surface of the rectifier diode 1N4007 was blackened, and the circuit board was also blackened. After replacing the diode of the same model, troubleshooting.
Example 2: The power supply keeps blowing the fuse. After investigation, it was found that the rectifier bridge, large electrolytic capacitor and primary switch tube were faulty. After the corresponding components are replaced, the problem is solved.
Summary: Repairing the power supply is not complicated, and common faults can be attributed to fuse blowing, rectifier diode damage, filter capacitor open circuit or breakdown, switch tube breakdown and power supply self-protection. Master enough basic knowledge of electronics, read relevant technical articles, accumulate practical experience, and power failures can be easily repaired.