Six Common Faults of Digital Multimeters
(1) If there is no display on the instrument, first check if the battery voltage is normal (usually a 9V battery is used, and new ones should also be measured). Secondly, check whether the fuse has been blown, whether the voltage regulator block is normal, and whether the current limiting resistor is open. Then, check if there is corrosion, short circuit, or open circuit on the circuit board (especially in the main power circuit). If there is, clean the circuit board and do a good job of drying and welding in a timely manner; If the circuit board is normal, the two pins of the power input of the display integrated block can be measured. Is the test voltage normal? If the test voltage is normal, the integrated block is damaged and must be replaced; If the test voltage is abnormal, check if there are any other short circuit points? If there is, it should be dealt with in a timely manner; If it is not present or if it still does not work properly after handling, then the integrated block has a short circuit inside and must be replaced.
(2) The resistance gear cannot be measured. Firstly, inspect the circuit board visually. Is there any connection or burnt out resistor in the resistance gear circuit? If there is, it must be replaced immediately; If not, measure each connecting component and replace any damaged ones in a timely manner; If the periphery is normal, then the measurement module is damaged and must be replaced.
(3) The inaccurate or even unstable indication of voltage during high voltage measurement is mostly caused by insufficient working power of one or several components. If these components are found to be hot during inspection within a few seconds of stopping the measurement, which is caused by thermal effects due to insufficient power, then the component (or integrated circuit) must be replaced.
(4) The inability to measure the current level is mostly caused by improper operation. Can you check if the current limiting resistor and voltage divider resistor are burned out? If burned out, it should be replaced; Then check if the connecting wire to the amplifier is damaged? If damaged, it should be reconnected; If it is not normal, replace the amplifier.
(5) Is the display unstable and there is a jumping word phenomenon? Check if the overall circuit board is damp or has leakage? If there is, the circuit board must be cleaned and dried properly; Check for poor contact or virtual soldering in the input circuit (including test pens). If there are any, they must be re soldered; Check if there is any resistance deterioration or if there are any components that experience abnormal hot hands after testing. This phenomenon is caused by a decrease in power. If this phenomenon occurs, the component should be replaced.
(6) The phenomenon of inaccurate readings is mainly caused by the failure of resistance or capacitance in the measurement circuit, and the capacitor or resistor must be replaced. Check the resistance value of the resistor in the circuit (including the resistance value in the thermal reaction). If the resistance value changes or the thermal reaction value changes, the resistor should be replaced; Check if the resistance and capacitance in the reference voltage circuit of the A/D converter are damaged? If damaged, replace it.
