Ways for fixing digital multimeters
Digital instruments have high sensitivity and accuracy, and their applications are found in almost all enterprises. However, due to the fact that there are many factors in the failure, and the randomness of the problems encountered is large, there are not many rules to follow, and the repair is difficult. Therefore, I have sorted out some repair experience accumulated in many years of work practice for the reference of colleagues engaged in this profession.
1. Repair method
When looking for faults, you should start from the outside and then the inside, first easy and then difficult, break the whole into parts, and make breakthroughs in key points. The methods can be roughly divided into the following categories:
1. The sensory method directly judges the cause of the fault by means of the senses. Through visual inspection, it can be found such as disconnection, desoldering, short circuit, broken fuse tube, burnt out components, mechanical damage, and copper foil warping on the printed circuit. You can touch the temperature rise of batteries, resistors, transistors, and integrated blocks, and you can refer to the circuit diagram to find out the reason for the abnormal temperature rise. In addition, by hand, you can also check whether the components are loose, whether the integrated circuit pins are firmly inserted, and whether the transfer switch is stuck; you can hear and smell whether there are abnormal sounds and odors.
2. Voltage measurement method: measure whether the working voltage of each key point is normal, and find out the fault point quickly. Such as measuring the working voltage and reference voltage of the A/D converter.
3. Short-circuit method In the method of checking the A/D converter mentioned above, the short-circuit method is generally used. This method is often used when repairing weak and micro-electric instruments.
4. Open circuit method Disconnect the suspicious part from the whole machine or unit circuit. If the fault disappears, it means that the fault is in the disconnected circuit. This method is mainly suitable for the situation where there is a short circuit in the circuit.
5. Measuring component method When the fault has been reduced to a certain place or several components, it can be measured online or offline. If necessary, replace it with a good one. If the fault disappears, the component is broken.
6. Interference method Use the human body induced voltage as the interference signal to observe the changes of the liquid crystal display, which is often used to check whether the input circuit and the display part are intact.
