Why does the digital multimeter shut down when using the peak setting?
It cannot be ruled out that the battery is running low. When using the buzzer mode, the buzzer is an inductive load, and the instantaneous voltage may be relatively high, which may pull down the low battery and cause the main chip to shut down directly due to insufficient voltage
If the battery remains the same after replacement, it may be caused by a short circuit or leakage in the buzzer or related drive circuit. There is no need to tinker anymore. A multimeter costs little and takes more time.
Or simply replace the buzzer and try it out. If it doesn't work, just buy a new one.
There are generally two situations when a digital multimeter automatically shuts down when using the buzzer mode. One is that the battery of the multimeter is old, and when the buzzer mode with high power consumption is working, the battery voltage drops significantly, causing the multimeter to automatically shut down; Another situation is that there is a malfunction in the buzzer mode, where the current during operation is high, resulting in a significant decrease in battery voltage and causing the multimeter to shut down. Below, we will provide a detailed introduction to the working principle and troubleshooting of the buzzer mode circuit of a digital multimeter.
CD4011 is a CMOS low-power quad 2 input NAND gate, which is connected here to form a voltage controlled audio oscillator. When testing the circuit on/off with the buzzer mode, if the resistance of the measured resistor Rx is ≤ 70 Ω (some are also set to other resistance values), pin ① of LM324 outputs a high level, causing the voltage controlled audio oscillator composed of CD4011 to work. The piezoelectric ceramic chip emits a buzzing sound, and at the same time, the LED indicator light also starts to light up.
The working current of other levels of a typical digital multimeter is mostly within 10mA, while the buzzer level consumes a relatively large amount of electricity due to the piezoelectric ceramic tiles and indicator lights. If the battery of the multimeter is old, it may cause a significant decrease in battery voltage, resulting in the multimeter shutting down.
In addition, if the CMOS gate circuit CD4011 or piezoelectric ceramic chip of the buzzer gear malfunctions, it will significantly increase the power consumption of the entire buzzer gear, which will also cause the multimeter to automatically shut down. The author has previously repaired faults with high power consumption in buzzer settings, mostly with CD4011 or piezoelectric ceramic chips. When there is a slight short circuit at both ends of a piezoelectric ceramic sheet, it will cause the buzzer to produce less sound and increase power consumption.
Piezoelectric ceramic sheet.
The piezoelectric ceramic plate used for the digital multimeter is shown in the above figure. This type of piezoelectric ceramic piece usually comes with an auxiliary sound chamber to increase the volume of the sound. The common fault of piezoelectric ceramic chips is the detachment of the surface ceramic layer.
The position of the buzzer gear on the digital multimeter.
The buzzer mode of a digital multimeter is usually combined with the diode mode, as shown in the above figure. When testing the circuit on/off using the buzzer mode, adjust the range switch to the diode mode position.
