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There are now fewer pointer multimeters in use and digital multimeters are currently measuring instruments.
Taking a sample and displaying the measurement results takes 0.3 seconds. Sometimes the results of each sampling are very similar and not exactly the same, which is not as convenient as the pointer type reads the results.
The internal structure of the needle multimeter is simple, so the cost is low, the function is smaller, the maintenance is easy, and the overcurrent and overvoltage ability is ;
Below I would like to detail the common repair methods for pointer multimeter failures:
1. Preliminary identification before the overhaul
Before the Overhaul first use a gauge that meets the requirements. Put the new battery in the clock, set the multimeter to R×1, R×10, R×100 or R×1k, connect the twon Short test leads and check if there is an indication on the clock hand.
If there is no indication, the cause is generally an open circuit of the fuse (0.5 A) or the meter coil.
To assess if the moving coil is damaged, solder one end of the meter head connector with a soldering iron, take another good multimeter and set it to R×1k to measure its resistance;
At the same time observe whether the moving coil is deflected. If the internal resistance of the moving coil of the counter head is 0 Ω or infinity and the moving coil does not deflect, it can be assumed that the counter head is defective:
An internal resistance of 0 Ω shows assumes the moving coil is shorted, and infinity is an open circuit. The unstable hands of The watch indicate a partial short circuit ora bad contact. If the moving coil does not deflect, this indicates that it is open or blocked by debris. Another check should be carried out.
2. Check the dc voltage and direct current files.
If the multimeter's dc voltage file is generally normal, the dc current file is normal most of the time; if the DC voltage levels are abnormal;
Then most DC levels will also have problems, with open circuits being more common.
A more sensible way to judge is to start testing in the mid-range. MF-30 has 50μA, 0.5mA, 5mA, 50mA, 500mA and other qualities and it is better to start with it from 5mA range:
If there is no reading in the 5mA range, the problem must be in the 0.5mA or 50μA range;
If the reading is too large, i.ehe error is in the 50 mA or 500 mA range.
3. Check AC voltage file and resistance file.
Based on normal DC voltage file and DC current file, check AC voltage file and resistance files further.
The errors in these two gears are usually expressed in large errors, pointer trembling, missing display and zero point setting.
When overhauling, you should first open the back cover of the multimeter to observe whether there are any obvious phenomena such as component burn-out or wire desoldering, and then analyze them using the schematic diagram and judge:
The error is large and no read occurs. Generally it is due to the change in the component value and the locality of the corresponding file.Short circuit, mold;
The pointer wobbles, usually because one of the two rectifiers is openor the corresponding component is open;
The Ω transition cannot be adjusted to zero, this is mostly caused by the battery depletion or the oxidation of the battery positive and negative electrodes and the surge caused by the contact resistance;
When Some gears cannot be zeroed (e.g. R×1 gear). Check that there is no obvious fault after that, mainly caused by the increase in the contact resistance of the range switch;
It can be applied with a small amount of clean lubricating oil, and then back and forth for a few weeks be rotated. If the oxidation is severe, it should be polished with fine sandpaper.
