When overhauling, it should be noted that the light-emitting element of this flashlight is a “light-emitting diode”, which has the characteristics of light-emitting, but also has the characteristics of unidirectional conduction and reverse breakdown of the diode. First check whether there is an open circuit in the circuit, whether the switch is in poor contact, whether the +- pole of the battery is corroded, etc. When testing with a multimeter, first determine whether there is a problem with the battery. Measure the voltage at both ends of the electrode. If the voltage is 0 or below the rated voltage, consider charging or replacing the battery. At the same time, check whether there is a problem with the charging circuit.
After confirming that there is no problem with the circuit and battery, check and repair the light-emitting diode. Use a multimeter ×1Kor ×100 gear (high resistance gear is not recommended, because its high voltage may easily cause the reverse breakdown of the light-emitting diode) to measure the positive and negative on-off of the light-emitting diode to determine whether the light-emitting diode is damaged. Most LED flashlights are connected by multiple light-emitting diodes in series or series-parallel connections, which can be tested in sections, and the damaged diodes can be found by the elimination method, and replaced with light-emitting diodes of the same model. Very correct. Pay attention to welding the positive and negative poles.