1. Use the resistance gear of the multimeter to check the quality of the electrolytic capacitor
The two leads of the electrolytic capacitor are divided into positive and negative. When checking whether it is good or bad, for the electrolytic capacitor with lower withstand voltage (6V or 10V), the resistance should be placed in the R×100 or R×1K gear. The red test lead is connected to the negative end of the capacitor, and the black test lead is connected to the positive end. At this time, the multimeter pointer will swing and then return to zero or near zero. Such electrolytic capacitors are good. The larger the capacity of the electrolytic capacitor, the longer the charging time and the slower the pointer swings.
2. Use a multimeter to judge the positive and negative leads of the electrolytic capacitor
For some electrolytic capacitors with low withstand voltage, if the positive and negative lead marks are unclear, it can be judged according to the characteristics of its small leakage current (large resistance value) when it is connected positively and large leakage current when it is connected reversely. The specific method is: touch the two leads of the capacitor with red and black test pens, remember the magnitude of the leakage current (resistance value) (the resistance value indicated when the pointer swings back and stops), and then short the positive and negative leads of the capacitor. Next, switch the red and black test pens before measuring the leakage current. Judgment is based on the indication value of the small leakage current. The lead that is in contact with the black test lead is the positive end of the electrolytic capacitor. This method is more difficult to distinguish the polarity of electrolytic capacitors with small leakage current.
3. Check the variable capacitor with a multimeter
A variable capacitor has a set of fixed pieces and a set of moving pieces. Use the resistance gear of the multimeter to check whether there is any contact between the moving and fixed pieces. Use red and black test pens to connect the moving piece and the fixed piece respectively, and rotate the shaft handle. The pointer of the meter does not move, indicating that there is no short circuit between the moving and fixed pieces ( touch the piece); if the pointer swings, it means that the capacitor has a short circuit.
4. Use the resistance gear of the multimeter to roughly identify the quality of the capacitance above 5000PF
Using the resistance gear of a multimeter can roughly identify the quality of capacitors above 5000PF (those below 5000PF can only judge whether the inside of the capacitor is broken down). When checking, put the resistance range at the high-end value of the range, and the two test leads are in contact with both ends of the capacitor. At this time, the pointer swings quickly and then recovers. Connected in reverse, the swing amplitude is larger than the first time, and then recovers. Such capacitors are good. The larger the capacity of the capacitor, the greater the swing of the meter pointer during measurement, and the longer the pointer recovery time. We can compare the capacity of the two capacitors according to the swing of the meter pointer.
