Use a multimeter to detect faulty circuits and find faulty components
Today I will teach you a simple way to use a multimeter to judge whether a component is burned out and whether it should be replaced.
The multimeter we use
Today I will take the broken mobile phone charger as an example to explain to you. This broken charger should be caused by excessive current during work, which melted the solder on the PCB and caused some components to burn directly. .
On the right side of the picture on the reverse side, we can see that the solder on the PCB has melted obviously. There is no direct way to detect such a problem with a multimeter. This phenomenon is also obvious. It can be seen at a glance. A thread was drawn from the melted ends and reattached.
In the picture on the front, you can also clearly see that the capacitor under the board has obviously bulged, indicating that it has been burned. Of course, we can check it with a multimeter. There is a small capacitor on the right side of the bulged capacitor, which seems complete. I don't know if it is broken, so we use a multimeter to test these two small components.
capacitance detection
Step 1: Adjust the multimeter to the capacitor mode to select the appropriate range
Step 2: Put the test leads of the multimeter on both ends of the two component pins
After testing with a multimeter, we can clearly see that the small capacitor is measured by the indication. Read the indication of the multimeter, and then compare the actual value marked on the capacitor. If the two values are close, then the capacitor is normal. Our capacitor is marked 10uf, and the measured value of 13.8uf can be said to be close.
Look at the second picture again, you can clearly see that the indication of the multimeter is directly zero, which is enough to show that the capacitor of the drum is indeed burnt, if you want to repair it, find a capacitor with the same parameters to replace this one .
Diode detection
After talking about the capacitance, let’s talk about the detection of the diode. The diode detection method is a little simpler than the capacitance detection, because our multimeter has a diode block, and there is only one position, so we don’t need to consider the problem of the range. We adjust it to the diode block. , and then connect the anode of the multimeter to the anode of the diode, and connect the cathode of the multimeter to the anode of the diode. If you see a reading on the display of the multimeter, it means that the diode in the circuit is normal (some multimeters will beep), and they are not damaged. breakdown.
Inductance detection
Inductance is a very important component in mobile phone chargers, almost every charger is indispensable, so we also need to learn a method to detect inductance, "inductance" we learned in high school, inductance is equivalent to a short circuit to DC, we This can be put to good use in combination with the diode block on the multimeter.
We all know that if the diode blocking red and black test leads are directly connected to a multimeter, it will make a sound, and if it is not connected, it will not make a sound. In addition to not ringing, there is only a diode symbol in the upper right corner of the multimeter's display.
Next, we connect the multimeter to both sides of the inductor, and then look at the changes on the display in the upper right corner of the multimeter display.
Is there another symbol similar to the signal of a mobile phone? It means that the inductance is normal and there is no open circuit. When this phenomenon occurs, you will still hear the buzzer beeping. At this time, we can be sure that the inductance is normal. .
