Common issues with digital multimeters and their maintenance
(1) There is no display on the instrument First, check whether the battery voltage is normal (9V batteries are generally used, and new ones should also be measured). Secondly, check whether the fuse is blown, whether the voltage regulator block is normal, and whether the current limiting resistor is open. Then, check the circuit board for corrosion, short circuit, or open circuit (especially the main power supply circuit). If so, clean the circuit board, and do a good job of drying and welding in time; The two pins of the power input, is the test voltage normal? If the test voltage is normal, the integrated block is damaged, and the integrated block must be replaced; if the test voltage is abnormal, check whether there are other short-circuit points? If so, it must be replaced in time If it is not or it is not normal after processing, then the integrated block has a short circuit inside and must be replaced.
(2) The electrical barrier cannot be measured. First, check the circuit board from the appearance. Is there any connection resistor burned out in the electrical barrier circuit? If so, it must be replaced immediately; if not, it is necessary to measure each connecting component. Replace it in time; if the periphery is normal, the measurement integrated block is damaged and must be replaced.
(3) The indication value of the voltage block is inaccurate when measuring high voltage, or the indication value is inaccurate or even unstable after measuring for a long time. Most of these faults are caused by the insufficient working power of one or several components. If within a few seconds of stopping the measurement, these components are found to be hot during inspection, which is caused by thermal effects caused by insufficient power, the component (or integrated circuit) must be replaced.
(4) The current block cannot be measured. Most of these faults are caused by improper operation. You can check whether the current limiting resistor and the voltage dividing resistor are burnt out? If they are burnt out, they should be replaced; then check whether the connecting wire with the amplifier is damaged? If it is damaged, it should be reconnected; if it is not normal, replace the amplifier.
(5) The display value is unstable, and there is a phenomenon of jumping characters. Check whether the overall circuit board is damp or has leakage. If so, the circuit board must be cleaned and dried; whether there is poor contact or virtual welding in the input circuit ( Including the test pen), if there is, it must be re-soldered; check whether there is any resistance deterioration or whether the components are super-normally hot after the test. This phenomenon is caused by the reduction of its power. If this phenomenon occurs, it should be Replace the element.
(6) Inaccurate indication This phenomenon is mainly caused by the failure of the resistance or capacitance in the measurement circuit, and the capacitance or resistance 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 response value changes, the resistor should be replaced; check whether the resistance and capacitance in the reference voltage circuit of the A/D converter are Damaged? Replace if damaged.
