Methods for Testing the Quality of Chargers with a Multimeter
Method 1: Use the resistance range or diode range of the multimeter to check whether the power input wire is open-circuited.
You can also plug the charger into the power supply. Use the DC voltage range to measure whether there is a DC voltage of about 300V on the high-voltage filter capacitor (EJ). If there is still no voltage, switch to the AC range to measure whether there is 220V AC input on the power input wire (BG). This helps to rule out faults caused by broken wires.
Inspection steps are as follows:
Use the multimeter's resistance range or diode range to measure BC, BD, GH, GI in sequence. All of these should be conductive. If any path is not conductive, that section has a fault. For example, if GH is conductive but GI is not, it means the common-mode filter has an open circuit (possibly a detached pin solder joint).
Next, use the multimeter's diode range to measure the forward voltage drop of the four diodes. Measure D→E, I→E, J→I, J→D in sequence (pay attention to polarity) and check if the values are normal. Abnormal readings indicate damaged diodes.
After completing the above troubleshooting steps, the fault can basically be located. These components may become loose due to vibration, resulting in detached solder joints and poor contact. Cold solder joints may be hard to spot visually, or even invisible. It is recommended to re-solder these components. The transformer can be removed for inspection.
Method 2: Power-on Test Method
Set the multimeter to the voltage range for voltage measurement. If no voltage is detected, disconnect the power supply and test the primary winding with the resistance range. A resistance value of several tens of ohms means it is in good condition; otherwise, it is damaged.
Test method: Connect one multimeter probe to the inner core of the cable and the other probe to the outer shell. Compare the voltage reading on the multimeter voltage range with the rated value. A reading around 7V indicates the charger is functional.
