Common Faults and Repairs of Digital Multimeter
(1) If there is no display on the instrument, first check if the battery voltage is normal (usually using a 9V battery, new ones should also be measured). Secondly, check if the fuse has blown, if the voltage regulator block is functioning properly, and if the current limiting resistor is open. Then, check if there is corrosion, short circuit, or open circuit on the circuit board (especially the main power circuit). If so, clean the circuit board and promptly dry and solder it; If the circuit board is normal, the two pins of the power input of the display integrated block can be measured to test whether the voltage is 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 promptly; If it is not functioning properly or is still not functioning properly after being processed, then the integrated block has already experienced a short circuit internally and must be replaced.
(2) Resistance gear cannot be measured. First, check the circuit board visually to see if there is a burnt 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, the measurement integrated block is damaged and must be replaced.
(3) Voltage blocking often results in inaccurate or unstable readings when measuring high voltage, or when measuring for a longer period of time. Such faults are 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, it is due to thermal effects caused by insufficient power, and the component (or integrated circuit) must be replaced.
(4) Current mode cannot measure such faults, which are mostly caused by improper operation. Can you check if the current limiting resistor and voltage divider resistor are burnt out? If burned out, it should be replaced; Then check if the connecting wires to the amplifier are damaged? If damaged, it should be reconnected; If it is not normal, replace the amplifier.
(5) Unstable readings and jumping 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 virtual soldering phenomenon (including test pen) in the input circuit? If so, it must be re soldered; Check for any resistance deterioration or abnormal overheating 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 readings is mainly caused by the failure of resistors or capacitors 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 thermal reaction). If the resistance value changes or the thermal reaction value changes, the resistor should be replaced; Check if the resistors and capacitors in the reference voltage circuit of the A/D converter are damaged? If damaged, replace it.
