Common faults and maintenance of digital multimeter
(1) If there is no display on the instrument, first check if the battery voltage is normal (usually 9V batteries are used, and new ones should also be measured). Secondly, check whether the fuse has blown, whether the voltage stabilizing block is normal, and whether the current limiting resistor is open. Then, check the circuit board for corrosion, short circuits, or open circuits (especially the main power circuit). If so, clean the circuit board and promptly dry and weld it; 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 not normal, check for 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 processing, then the integrated block has an internal short circuit and must be replaced.
(2) Unable to measure the resistance gear. Firstly, visually inspect the circuit board. Is there any connection or burnt out resistance in the resistance gear circuit? If any, it must be replaced immediately; If not, measure each connecting component and replace any damaged components in a timely manner; If the periphery is normal, the measuring integrated block 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, the component (or integrated circuit) must be replaced.
(4) The inability to measure the current level is mostly caused by improper operation. Can the current limiting resistor and voltage divider resistor be checked for damage? If burnt 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 word skipping phenomenon? Check if the overall circuit board is damp or has leakage? If there is, the circuit board must be cleaned and dried properly; Is there any contact * * or solder joints (including test pens) in the input circuit? If so, it must be re welded; Check for resistance deterioration or abnormal hand burning of components after testing, which is caused by a decrease in power. If this phenomenon occurs, the component should be replaced.
(6) The phenomenon of inaccurate indication is mainly caused by the failure of resistance or capacitance in the measuring circuit, and the capacitor or resistance must be replaced. Check the resistance value of the resistance in the circuit (including the resistance value in the thermal reaction). If the resistance value changes or the thermal reaction value changes, the resistance 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.
