Maintenance and Repair of Digital Multimeters
1. Maintenance
The digital multimeter is a precision electronic instrument, do not change the circuit at will, and pay attention to the following points:
1. Do not connect to DC voltage higher than 1000V or AC RMS voltage higher than 700V.
2. Do not connect the voltage source when the function switch is in the Ω and position.
3. Please do not use this watch when the battery is not installed or the back cover is not tightened.
2. Repair method
Digital multimeters are highly sensitive and accurate and are used in almost every enterprise. 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. Some repair experiences accumulated in the actual work are sorted out for reference by colleagues engaged in this major.
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:
⒈Feeling method relies on the senses to directly judge the cause of the fault. Through visual inspection, it can be found such as disconnection, desoldering, short circuit, broken fuse tube, burned components, mechanical damage, and copper foil on the printed circuit. And fracture, etc.; you can touch the temperature rise of the battery, 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.
⒉Measurement voltage method Measure whether the working voltage of each key point is normal, and can quickly find out the fault point. Such as measuring the working voltage and reference voltage of the A/D converter.
⒊Short-circuit method The short-circuit method is generally used in the inspection method of the A/D converter mentioned above. This method is often used in the repair of 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.
