고장난 계기의 경우 먼저 고장 현상이 공통적인지(모든 기능을 측정할 수 없음) 개별적인지(개별 기능 또는 개별 범위)를 확인하고 판단한 후 상황을 구별하여 문제를 해결합니다.
⒈ If all gears cannot work, focus on checking the power supply 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 power supply of the meter under test, and connect the negative test lead to the positive power supply (for digital multimeters), switch the switch to the diode measurement gear, if the display shows If it is the forward voltage of the diode, 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 circuit breaking method to gradually disconnect the components that use the power supply, focusing on checking operational amplifiers, timers, and A/D converters. If a short circuit occurs, more than one integrated component is generally damaged. The A/D converter can be checked at the same time as the basic meter, which is equivalent to the DC meter of an analog multimeter. The specific inspection method is as follows:
⑴ The range of the meter under test is turned to the lowest level of DC voltage;
(2) A/D 변환기의 작동 전압이 정상인지 측정합니다. V plus 핀과 COM 핀에 해당하는 표에 사용된 A/D 변환기 모델에 따라 측정값을 일반 값과 비교합니다.
(3) A/D 변환기의 기준 전압을 측정합니다. 일반적으로 사용되는 디지털 멀티미터의 기준 전압은 일반적으로 100mV 또는 1V입니다. 즉, VREF plus와 COM 사이의 DC 전압을 측정합니다. 100mV 또는 1V에서 벗어나면 외부 전위차계로 조정할 수 있습니다.
⑷ Check the displayed number of input zero, short{{0}}circuit the positive terminal IN plus of the A/D converter with the negative terminal IN-, make the input voltage Vin=0, and the meter displays "00.0" or "00.00".
⑸ Check the full bright stroke of the display. Short-circuit the test terminal TEST pin with the positive power supply terminal V plus to make the logic ground become a high potential, and all digital circuits stop working. Because DC voltage is applied to each stroke, all strokes are bright and the alignment table displays "1888", and the alignment table displays "18888". If there is a missing stroke, check the corresponding output pin of the A/D converter and the conductive glue (or connection), and check whether there is poor contact and disconnection between the A/D converter and the display.
⒉ If there is a problem with individual files, it means that the A/D converter and the power supply part are working normally. Because DC voltage and resistance files share a set of voltage divider 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 diagram, it is easy to find the fault location. If the measurement of the small signal is inaccurate or the displayed number jumps greatly, focus on checking whether the contact of the range switch is good.
3. If the measured data is unstable, and the value always increases cumulatively, the input terminal of the A/D converter is short-circuited, and the displayed data is not zero, which is generally caused by the poor performance of the 0.1μF reference capacitor.
According to the above analysis, the basic sequence of repairing the digital multimeter should be: digital meter head→DC voltage→DC current→AC voltage→AC current→resistance gear (including buzzer and checking diode positive voltage drop)→Cx→HFE , F, H, T, etc. But it should not be too mechanical. Some obvious problems can be dealt with first. But when making adjustments, be sure to follow the above procedure.
간단히 말해서, 결함이 있는 멀티미터는 적절한 테스트 후 먼저 결함의 가능한 부분을 분석한 다음 교체 및 수리를 위한 회로도에 따라 결함 위치를 찾아야 합니다. 디지털 멀티미터는 비교적 정밀한 기기이기 때문에 교체 부품은 동일한 매개변수를 가진 부품으로 교체해야 하며 특히 A/D 변환기 교체는 제조업체에서 엄격하게 검사한 통합 블록을 사용해야 합니다. 그렇지 않으면 오류이며 요구 사항을 충족하지 않습니다. 정확성. 새로 교체한 A/D 컨버터도 위와 같은 방법으로 점검을 받아야 하며, 새것이라 믿으면 안됩니다.
GVDA Digital Multimeter GD108A:
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