Per a un instrument defectuós, primer comproveu i determineu si el fenomen d'error és comú (no es poden mesurar totes les funcions) o individual (funcions individuals o rangs individuals), i després distingiu la situació i resoleu el problema.
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) Mesureu si la tensió de treball del convertidor A/D és normal. Segons el model de convertidor A/D utilitzat a la taula, corresponent al pin V més i al pin COM, compareu el valor mesurat amb el seu valor típic.
(3) Mesureu la tensió de referència del convertidor A/D. La tensió de referència del multímetre digital d'ús habitual és generalment de 100 mV o 1 V, és a dir, es mesura la tensió de CC entre VREF plus i COM. Si es desvia de 100mV o 1V, es pot ajustar mitjançant un potenciòmetre extern.
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.
En resum, un multímetre defectuós, després de les proves adequades, primer ha d'analitzar les possibles parts de la falla i, a continuació, trobar la ubicació de la falla segons el diagrama de circuits per a la seva substitució i reparació. Com que el multímetre digital és un instrument relativament precís, els components de substitució s'han de substituir per components amb els mateixos paràmetres, especialment la substitució del convertidor A/D, ha d'utilitzar el bloc integrat que ha estat estrictament controlat pel fabricant, en cas contrari, hi haurà ser errors i no complir els requisits. Precisió. El convertidor A/D recentment substituït també s'ha de comprovar d'acord amb el mètode descrit anteriorment i no s'ha de confiar a causa del nou.
GVDA Digital Multimeter GD108A:
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