What are the digital multimeter's repair capabilities
1. If all gears fail to work, focus on checking the power circuit and A/D converter circuit. When checking the power supply part, you can remove the laminated battery, press the power switch, connect the positive test lead to the negative of the power supply of the meter under test, and the negative test lead to the positive power supply (for digital multimeters), and switch to the diode measurement position. If the forward voltage of the diode is higher, it means that the power supply part is good. If the deviation is large, it means that there is a problem with the power supply part. If there is an open circuit, focus on checking the power switch and battery leads. If there is a short circuit, you need to use the open circuit method to gradually disconnect the components that use the power supply, and focus on checking the operational amplifier, timer and A/D converter. In the event of a short circuit, generally more than one integrated component is damaged. Checking the A/D converter can be carried out simultaneously with the basic meter, which is equivalent to the DC meter head of the analog multimeter. The specific checking method:
(1) The range of the meter under test is turned to the lowest level of DC voltage;
(2) Measure whether the working voltage of the A/D converter is normal. According to the A/D converter model used in the table, corresponding to V+ pin and COM pin, whether the measured value is consistent with its typical value.
(3) Measure the reference voltage of the A/D converter. The reference voltage of the commonly used digital multimeter is generally 100mV or 1V, that is, measure the DC voltage between VREF+ and COM. If it deviates from 100mV or 1V, you can use an external potentiometer Make adjustments.
(4) Check the display number whose input is zero, short-circuit the positive terminal IN+ and the negative terminal IN- of the A/D converter, so that the input voltage Vin=0, and the meter displays "00.0 or "00.00.
(5) Check the full brightness strokes of the display. Short the test terminal TEST pin and the positive power supply terminal V+, make the logic ground become high potential, and all digital circuits stop working. Because DC voltage is added to each stroke, all strokes are bright and the alignment table shows "1888, and the alignment table shows "18888. If there is a lack of strokes, check whether there is any poor contact or disconnection between the corresponding output pin of the A/D converter and the conductive glue (or connection), and the display.
2. If there is a problem with individual files, it means that the A/D converter and the power supply are working normally. Because DC voltage and resistance files share a set of voltage dividing resistors; AC and DC current share a shunt; AC voltage and AC current share a set of AC/DC converters; others such as Cx, HFE, F, etc. are composed of independent different converters . Understand the relationship between them, and then according to the power supply diagram, it is easy to find the fault location. If the measurement of small signals is inaccurate or the displayed number jumps greatly, then focus on checking whether the contact of the range switch is good.
3. If the measurement data is unstable, and the value always increases cumulatively, short the input terminal of the A/D converter, and the displayed data is not zero, it is generally caused by the poor performance of the 0.1μF reference capacitor.
