Multimeter troubleshooting steps and precautions
(1) Turn the range of the tested meter to the lowest level of DC voltage;
(2) Measure whether the operating voltage of the A/D converter is normal. According to the model of the A/D converter used in the table, corresponding to the V+and COM pins, compare the measured values with their typical values to see if they match.
(3) Measure the reference voltage of the A/D converter. The commonly used digital multimeter reference voltage is generally 100mV or 1V, which measures the DC voltage between VREF+and COM. If it deviates from 100mV or 1V, it can be adjusted by an external potentiometer.
(4) Check the display number with zero input, short circuit the positive terminal IN+and negative terminal IN - of the A/D converter to make the input voltage Vin=0, and the instrument will display "00.0" or "00.00".
(5) Check the fully lit strokes on the monitor. Short circuit the test terminal TEST pin to the positive power terminal V+, causing the logic ground to become high and all digital circuits to stop working. Due to the direct current voltage applied to each stroke, all strokes are lit up and the alignment table displays "1888" and "18888". If there is a missing stroke, check whether there is poor contact or wire breakage between the corresponding output pin of the A/D converter and the conductive adhesive (or wiring), and between the A/D converter and the display.
Precautions for measuring with a multimeter
(1) Before measurement, disconnect the power supply to avoid damaging the meter and components during testing.
(2) The internal voltage of the multimeter resistor range should not exceed 6V, and the range should be set to r × 100 or r × 1k.
(3) When measuring the parameters of IC pins, attention should be paid to the measurement conditions, such as the tested model, the position of the sliding arm of the potentiometer related to IC, and the quality of peripheral circuit components.
