A digital multimeter can be said to be a must-have tool for every engineer. Through a digital multimeter, we can measure many different circuit data, and then help us check this circuit and whether there is a problem with this electrical appliance. But many times we will find that our digital multimeter is damaged. How to repair the digital multimeter? Then the editor will introduce to you the reasons why our digital multimeter is damaged, and how we should solve the damage of the digital multimeter!
Causes of damage to the digital multimeter
In most cases, the damage of the digital multimeter is caused by the wrong measurement gear. For example, when measuring AC mains, the measurement gear is selected to be placed on the electric block. In this case, once the pen contacts the mains, the internal components of the multimeter can be damaged instantly. . Therefore, be sure to check whether the measurement gear is correct before using the multimeter to measure. After use, set the measurement selection to AC 750V or DC 1000V, so that no matter what parameter is wrongly measured in the next measurement, it will not cause damage to the digital multimeter.
The damage of some digital multimeters is caused by the measured voltage and current exceeding the range. For example, when measuring the mains power in the AC 20V range, it is easy to cause damage to the AC amplifier circuit of the digital multimeter, and the multimeter loses the AC measurement function. When measuring DC voltage, the measured voltage exceeds the measurement range, which is also likely to cause circuit failure in the meter. When measuring the current, if the actual current value exceeds the range, it will generally only cause the fuse in the multimeter to blow, and no other damage will be caused. Therefore, when measuring voltage parameters, if you do not know the approximate range of the measured voltage, you should first set the measurement gear to the highest gear, and then change the gear to measure the value to obtain a more accurate value. If the voltage value to be measured is far beyond the maximum range that the multimeter can measure, a high-resistance measurement lead should be provided. Such as detecting the second anode high voltage and focusing high voltage of black and white color TV.
The DC voltage upper limit range of most digital multimeters is 1000V, so the maximum voltage value when measuring DC voltage is below 1000V, which generally will not damage the multimeter. If it exceeds 1000V, it is very likely to cause damage to the multimeter. However, the upper limit of the measurable voltage may be different for different digital multimeters. If the measured voltage exceeds the range, the method of reducing the resistance of the resistor can be used to measure it. In addition, when measuring 400-1000V DC high voltage, the test leads must be in good contact with the measurement place, and there should be no jitter. Otherwise, in addition to causing damage to the multimeter and making the measurement inaccurate, the multimeter can also be used in serious cases. show.
Multimeter failure and repair
How to repair the digital multimeter
The maintenance of digital multimeters should be done first from the outside to the inside, from the easy to the difficult. The methods can be roughly divided into the following categories:
1. Sensation
By means of the senses to directly judge the cause of the failure, through the visual inspection, it can be found such as disconnection, de-soldering, short-circuiting, broken fuse tube, burnt components, mechanical damage, and copper foil 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, you can also check by hand whether the components are loose, whether the integrated circuit pins are firmly inserted, and whether the transfer switch is cassette; you can hear and smell whether there is any abnormal sound or smell.
2. Voltage measurement method
Measure whether the working voltage of each key point is normal, which can quickly find out the fault point. Such as measuring the working voltage of the A/D converter, the reference voltage, etc.
3. Short circuit method
The short-circuit method is generally used in the method of checking the A/D converter mentioned above. This method is often used in the repair of weak and micro-electrical instruments.
4. Circuit breaking 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 short circuits in the circuit.
5. Measuring element method
When the fault has been narrowed down to a place or a few components, it can be measured online or offline. If necessary, replace with good components. If the fault disappears, the components are broken.
Generally speaking, if the digital multimeter is damaged, it is often caused by our improper operation. For example, when we are testing a DC circuit, we use the gear of the AC circuit for testing. In fact, such an operation is very damaging to our digital multimeter.
