Multimeter frequency function mainly repair what commonly used
First, the repair method to find the fault should be the first outside after the inside, the first easy after the difficult, the whole into zero, focus on breakthroughs. The method can be broadly divided into the following categories:
Feeling method
By virtue of the senses directly to the cause of the failure to make a judgement, through the appearance of the inspection, can be found, such as broken wires, de-welding, short-circuit lap wire, fuse tube broken, burnt components, mechanical damage, copper foil on the printed circuit warping and fracture, etc.; you can touch out of the battery, resistors, transistors, integrated blocks of the temperature rise, you can refer to the circuit diagrams to find out the reasons for the temperature rise abnormalities. In addition, the hand can also check whether the components are loose, integrated circuit foot tube is firmly inserted, the changeover switch is not cassette; can hear and smell the sound, odour.
Measure the voltage method
Measurement of the key points of the operating voltage is normal, you can quickly find the point of failure. Such as measuring the A/D converter voltage, reference voltage.
Short circuit method
In the previously mentioned methods of checking the A/D converter are generally used in the short-circuit method, this method in the repair of weak electrical and microelectronic instruments used more.
Disconnection method
Disconnect the suspicious part from the whole machine or unit circuit, if the fault disappears, it means that the fault is in the disconnected circuit. This method is mainly suitable for the presence of a short circuit in the circuit.
Component Measurement Method
When the fault has been narrowed down to a certain place or a few components, they can be measured online or offline. If necessary, replace it with a good component, if the fault disappears, it means that the component is bad.6. Interference method The use of human induced voltage as an interference signal, observe the changes in the liquid crystal display, often used to check the input circuit and the display part is intact.
Second, repair skills on a piece of fault instrumentation should first check and identify the fault phenomenon is common (all functions can not be measured), or personality (individual functions or individual range), and then differentiate between the situation, to solve the problem.
If all the gear 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 digital multimeter), the switch hit to the secondary tube measurement file, if the display is the secondary tube positive voltage, it means that the power supply part of the good, if the deviation is large, then 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, so all strokes are bright para-meter display "1888, para-meter display "18888. If there is a lack of strokes, check the A/D converter corresponding to the output pin and the conductive rubber (or line), and the display of poor contact and disconnection between the situation.
