The identification of the positive and negative electrodes of the patch diode is usually observed in the tube shell. When the face of the case is serious, it can be used to determine the resistance of the universal meter. The schematic diagram of the test is shown in Figure 1. In Figure 1, the multimeter is placed in the R or R * * 100 Omega 1 K ohm, first with the red and black two probe resistance meter measuring arbitrary value between two pin diode chip, and then swap pen measured once again. In the two measurement results, choose a smaller value as the standard, the end of the black pen for positive patch diode, the other end is connected to the cathode of the red pen LED; the measured resistance is led forward resistance (usually a few hundred ohms to several thousand ohms), another group of resistance SMD reverse resistance (typically tens of ohms to several hundred ohms).