Multimeter repair tips for a faulty meter should first check the
If all gears can not work, should focus on checking the power supply circuit and A/D converter circuit. Check the power supply part, you can remove the laminated battery, press the power switch, with a positive pen connected to the measured table power supply negative, negative pen connected to the power supply positive (for the digital multimeter), the switch hit to the secondary tube measurement file, if the display is the secondary tube positive voltage, then the power supply part of the good, if the deviation is large, it means that the power supply part of the problem. If there is an open circuit, focus on checking the power switch and battery leads, etc.. If there is a short circuit, it is necessary to use the disconnection method to gradually disconnect the components that use the power supply, focusing on checking the operational amplifiers, timers and A/D converters. If a short circuit occurs, it usually damages more than one integrated component. Checking the A/D converter can be carried out at the same time with the basic meter, equivalent to the DC head of the analogue multimeter.
Specific inspection methods:
(1) the range of the measured table to the lowest DC voltage gear.
(2) Measure whether the A/D converter operating voltage is normal. According to the model of the A/D converter used in the table, corresponding to the V + pin and COM pin, the measured value compared with its typical value is consistent.
(3) Measure the reference voltage of the A/D converter, the reference voltage of the commonly used digital multimeter is generally 100mV or 1V, i.e., measure the DC voltage between VREF+ and COM, if it deviates from 100mV or 1V, it can be adjusted by external potentiometer.
(4) Check the number of displays where the input is zero, short the positive terminal IN+ and the negative terminal IN- of the A/D converter so that the input voltage Vin=0 and the instrument displays "00.0 or "00.00.
(5) Check the display for full bright strokes. Short the test terminal TEST pin to the positive power supply terminal V+ so that the logic ground becomes high potential and all digital circuits stop working. Because of the DC voltage added to each stroke, all strokes are bright and the counter display shows "1888, the counter display shows "18888. If there is a lack of strokes, check the corresponding output pin of the A/D converter and the conductive rubber (or wire), and the display of poor contact and disconnection between the situation.
