Positive and negative polarization of SMD electrolytic capacitor
The positive and negative poles of the SMD electrolytic capacitor are distinguished and the black block with the mark on the measuring capacitor is the negative pole. There are two semicircles on the position of the capacitor on the PCB, and the pin corresponding to the semicircle of the color is the negative pole. Also use the length of the pin to distinguish the positive and negative long legs from positive and the short legs to negative.
When we don't know the positive and negative poles of the capacitor, we can use a multimeter to measure. The medium between the two poles of the capacitor is not an absolute insulator, and its resistance is not infinite, but a finite value, generally above 1000 megohms. The resistance between the two poles of the capacitor is called an insulation resistance or a leakage resistance. Only when the positive electrode of the electrolytic capacitor is connected to the power supply (the black test pen when the power is blocked), and the negative terminal is connected to the negative power supply (the red test pen when the power is blocked), the leakage current of the electrolytic capacitor is small (the leakage resistance is large). On the contrary, the leakage current of the electrolytic capacitor increases (the leakage resistance decreases). In this way, we first assume that a very "+" pole, the multimeter uses R*100 or R*1K block, then the hypothetical "+" pole is connected with the black test pen of the multimeter, and the other electrode is connected with the red test pen of the multimeter. Record the scale of the needle stop (the needle has a large left value), and the digital multimeter can read the reading directly. Then discharge the capacitor (two leads touch), then the two test leads are reversed and the measurement is repeated. In the two measurements, the last position of the hand is left (or the resistance is large), and the black pen is connected to the positive electrode of the electrolytic capacitor.
Chip capacitor positive and negative
One is a common tantalum capacitor, which is in the shape of a rectangular parallelepiped, and one end marked with a "-" is positive;
There is also a silver surface mount capacitor, which should be aluminum electrolysis. The top is round and the bottom is square, which is common on optical drive boards. This type of capacitor is negative at the end marked with a "-".