Maintenance method of digital multimeter
1 Basic principles of maintenance
When overhauling the digital multimeter, it should be carried out according to the circuit diagram and the printed circuit board and component layout diagram.
When the cause of the failure is not determined, do not turn on the power. Because if there is a local short circuit fault, rushing to power is likely to cause greater losses. That is, analyze first, then do it; check first, then repair.
Overhauling a digital multimeter is a painstaking and meticulous work, and sometimes it takes a lot of energy. After repairing a digital multimeter, there will always be something to gain and new experience. Therefore, it is very important to continuously accumulate data and summarize experience. Some special failures have very little chance of occurring, and it takes a lot of trouble to eliminate them. Recording them will be more valuable for future work. The repair process is also a process of practice-theory-re-practice.
2 Intuitive method
The intuition method is a method that does not use electrical measurement means, but relies on human sense organs to judge the cause of the fault. When beginners assemble, due to unfamiliar operation, obvious technological errors are caused. Most of the faults are caused by short circuit, open circuit and component damage. Some of the reasons can be found through visual inspection.
For example, faults such as broken wires, desoldering, burnt resistors, reversed polarity of electrolytic capacitors and diodes, mechanical damage, broken copper foil of printed circuits or solder bonding can be seen. There is a short circuit. You can also smell a special smell, such as the burnt smell when the insulating layer of the resistance element is burned. You can also find out if the temperature rise of batteries, resistors, transistors, and integrated circuits is too high, whether components are loose, whether the range changeover switch rotates flexibly, whether steel balls fall off, etc. If the newly installed battery heats up, there is a short circuit.
The limitation of the intuition method is that sometimes only the superficial phenomenon or consequence of the failure is observed, rather than the cause of the failure.
3 voltage measurement method
When the electronic equipment is working normally, the voltage at each pin, contact or measuring point has a specified value or value range. Detecting the working voltage value of these points can judge whether the equipment is working normally, and can also detect the fault range or determine the fault point.
4 Short circuit method
Short-circuiting some pins of components or between pins and ground is to create a special working state for components. By observing whether the instrument responds correctly, it can be judged whether the component is faulty.
5 Waveform method
Observing the voltage waveform, amplitude and period (frequency) of each key point in the circuit with an oscilloscope can judge whether the dynamic working process of electronic equipment is correct or not, and find some faults where the static working voltage is normal but the dynamic working is abnormal [5].
