What's wrong with the digital multimeter screen having a digital display function that can't be used
There are generally two possibilities for this situation to occur. Firstly, there is a malfunction in the probe and input channel of the measured parameter, causing the analog-to-digital converter in the multimeter to be unable to read the signal; The second issue is that the internal analog-to-digital converter of the multimeter is damaged. Below, we will introduce these two situations separately.
1. Quick judgment of the quality of a multimeter analog-to-digital converter
The questioner said that the display screen has a display and the function is not functional. If the data displayed on the display screen is disorganized and a multimeter is used to measure parameters such as voltage and resistance, the numbers displayed on the multimeter will not change. At this point, we need to suspect whether the analog-to-digital converter inside is faulty. Here, with a regular 3 ½ Taking ICL7106, a commonly used analog-to-digital converter in digital multimeters, as an example, let's introduce the quick judgment of the quality of analog-to-digital converters. As shown in the above figure, 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 COM terminal (pin 32) of ICL7106, and this voltage does not change with the battery voltage of the multimeter. Therefore, we only need to measure the voltage between pin 1 and pin 32 of ICL7106 with another multimeter to see if it is the above value. If the measured voltage deviates greatly from the above voltage, it can be basically judged that there is a problem with the analog-to-digital converter or its peripheral components. At this point, you can first check the external components of ICL7106, and then determine if ICL7106 is damaged.
2. Diagnosis of multimeter probe and input channel faults
After confirming that there is no problem with the analog-to-digital converter of the digital multimeter, you can first set the range switch to the DC 200mV range, check if the number displayed on the display screen is "000.0", set it to the resistance range, and check if the number displayed is "1". If the range switch is rotated and the displayed number changes, it means that the internal wire of the probe is broken. In this case, the resistance level or buzzer level can be used to determine which probe is faulty. In addition, there is a fuse in the input terminal of the current range of 200mA and below on the digital multimeter. If this fuse burns out, it will cause the current range to be unusable.
