Tips til reparation af digitalt multimeter
For et defekt instrument skal du først kontrollere og afgøre, om fejlfænomenet er almindeligt (alle funktioner kan ikke måles) eller individuelt (individuelle funktioner eller individuelle områder), og derefter skelne situationen og løse den symptomatisk.
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:
⑴The range of the meter under test is turned to the lowest level of DC voltage;
(2) Mål om A/D-konverterens arbejdsspænding er normal. Sammenlign den målte værdi med dens typiske værdi i henhold til A/D-konvertermodellen i tabellen, svarende til V plus-benet og COM-stiftet.
(3) Mål referencespændingen for A/D-konverteren. Referencespændingen for det almindeligt anvendte digitale multimeter er generelt 100mV eller 1V, det vil sige, at DC-spændingen mellem VREF plus og COM måles. Hvis den afviger fra 100mV eller 1V, kan den justeres med et eksternt potentiometer.
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.
Kort sagt skal et defekt multimeter efter korrekt test først analysere de mulige dele af fejlen, og derefter finde fejlstedet i henhold til kredsløbsdiagrammet til udskiftning og reparation. Fordi det digitale multimeter er et relativt præcist instrument, skal udskiftningskomponenterne erstattes af komponenter med de samme parametre, især udskiftningen af A/D-konverteren, skal bruge den integrerede blok, der er blevet strengt screenet af producenten, ellers vil der være fejl og vil ikke opfylde kravene. Nøjagtighed. Den nyligt udskiftede A/D-konverter skal også kontrolleres i henhold til metoden beskrevet ovenfor, og den må ikke stoles på på grund af den nye.
