Why can't the digital display function on the digital multimeter screen be used?
When this happens, there are generally two possibilities. One is that the test leads and the input channel of the measured parameter are faulty, causing the analog-to-digital converter in the multimeter to be unable to read the signal; the other is that the analog-to-digital converter inside the multimeter is damaged. Below we introduce these two situations respectively.
1. Quickly judge the quality of the multimeter's analog-to-digital converter
The questioner said that there is a display on the display but the function cannot be used. If the data displayed on the display is messy and the numbers displayed by the multimeter do not change when a multimeter is used to measure parameters such as voltage and resistance, then we have to wonder whether the analog-to-digital converter inside is broken. Here we take the analog-to-digital converter ICL7106, which is 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 change of the multimeter battery voltage, so we only need to use Another multimeter measures the voltage between pin 1 and pin 32 of 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 first check the external components of the ICL7106, and then determine whether the ICL7106 is damaged.
2. Judgment of multimeter pen and input channel faults
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 position to see if the number displayed on the display is "000.0", and adjust it to the resistance position to see if the number displayed is "000.0". 1". If the range switch is rotated and the displayed number becomes variable, it means that the test lead is internally disconnected. At this time, you can use the resistance or buzzer setting to determine which test lead has a problem. In addition, the digital multimeter's 200mA and below current range input terminal has a fuse in series. If the fuse blows, the current range will become unusable.
