The screen of the digital multimeter has a digital display function, but what is going on?
In this case, there are generally two possibilities. One is that the test pen and the input channel of the measured parameter are faulty, causing the analog-to-digital converter in the multimeter to fail to read the signal; the other is that the analog-to-digital converter inside the multimeter is damaged. Below we introduce these two situations separately.
1. Quickly judge whether the analog-to-digital converter of the multimeter is good or bad
If the data displayed on the display is disorganized, and the multimeter is used to measure parameters such as voltage and resistance, and the numbers displayed by the multimeter will not change, then we must suspect that the analog-to-digital converter inside is broken. Here we take the analog-to-digital converter ICL7106 commonly used in ordinary 3½-digit digital multimeters as an example to introduce the quick judgment of the quality of the analog-to-digital converter. As shown in the figure above, it is a 200mV DC voltmeter composed of ICL7106. During normal operation, there is a stable voltage of 2.8-3.0V between the V+ terminal (pin 1) and the COM terminal (pin 32) of the ICL7106, and this voltage will not change with the voltage of the battery of the multimeter, so we only need to use Another multimeter measures the voltage between pin 1 and pin 32 of the ICL7106 to see if it is the above value. If the measured voltage deviates greatly from the above voltage, it can basically be judged that there is a problem with the analog-to-digital converter or its peripheral components. At this time, you can check the external components of the ICL7106 first, and then determine whether the ICL7106 is damaged.
Judgment of failures of multimeter pens and input channels
After confirming that there is no problem with the analog-to-digital converter of the digital multimeter, you can first adjust the range switch to the DC 200mV range to see if the number displayed on the display is "000.0", and then adjust it to the resistance range to see if the displayed number is "000.0". 1". If the range switch is turned and the displayed number is variable, it means that the internal wire of the test lead is broken. At this time, it can be judged which test lead is faulty through the resistance gear or the buzzer gear. In addition, there is a fuse in series with the input terminal of the current range of 200mA and below of the digital multimeter. If the fuse is blown, the current range will be unusable.
