No display, low output voltage, no load:

　　This type of defect first eliminates the defective battery cell (the battery cell originally has no voltage or the voltage is low). If the battery cell is defective, the self-consumption of the protection board should be tested to see if the self-consumption of the protection board is too large and the battery voltage is low. If the cell voltage is normal, it is because the entire circuit of the protection board is blocked (components are soldered, false soldered, FUSE is poor, the internal circuit of the PCB board is blocked, the via is blocked, MOS, IC is damaged, etc.). detailed analysis

　　Proceed as follows:

　　(1) Connect the black test lead of a multimeter to the negative electrode of the battery cell, and connect the red test lead to the FUSE, R1 resistor terminals, the Vdd, Dout, and Cout terminals of the IC, and the P+ terminal (assuming the battery cell voltage is 3.8V), and analyze it section by section. These test points should all be 3.8V. If not, there is a problem with this section of the circuit.

　　1. The voltage at both ends of the FUSE changes: test whether the FUSE is turned on, if it is turned on, the internal circuit of the PCB board is not turned on; if it is not turned on, there is a problem with the FUSE (poor incoming material, overcurrent damage (MOS or IC control failure), There is a problem with the material (the FUSE is burned out before the MOS or IC is activated), then use a wire to short the FUSE, and continue to analyze later.

　　2. There is a change in the voltage across the R1 resistor: test the resistance value of R1. If the resistance value is abnormal, it may be a virtual weld and the resistor itself is broken. If the resistance value is not abnormal, there may be a problem with the internal resistance of the IC.

　　3. There is a change in the voltage of the IC test terminal: the Vdd terminal is connected to the R1 resistor. Dout, Cout end abnormal, it is due to the IC weak welding or damage.

　　4. If there is no change in the previous voltage: the voltage between test B- and P+ is abnormal, it is because the positive through hole of the protection plate is blocked.

　　(2). Connect the red test lead of the multimeter to the positive electrode of the battery. After activating the MOS tube, the black test lead is connected to the MOS tube 2, 3, 6, 7 and P- terminal in turn.

　　1. If the voltage of MOS tube 2, 3, 6 and 7 has changed, it means the MOS tube is abnormal.

　　2. If there is no change in the MOS tube voltage and the P- terminal voltage is abnormal, it is because the negative via of the protection plate is blocked.