Welcome to Qinsun Instruments Co., Limited.
- +86-21-6780 0179 |
- info@qinsun-lab.com |
- Customer Services
There are now fewer pointer multimeters in use and digital multimeters are currently measuring instruments.
It takes 0.3 seconds to take a sample and display the measurement results. Sometimes the results of each sampling are very similar and not exactly the same, which is not as convenient for reading the results as the pointer type.
The internal structure of the needle multimeter is simple, so the cost is low, the function is smaller, the maintenance is simple, and the overcurrent and overvoltage resistance is high;
Let's talk about the common repair methods of the pointer multimeter in detail:
1. Preliminary identification before maintenance
Before maintenance, first put a new battery in the meter that meets the requirements, and set set the multimeter to R×1, R×10, R×10 0 or R×1k gear, short the two test leads to see, if there is any indication on the hands;
If there is no indication, this is generally caused by the open circuit of the fuse (0.5A) or coil of the meter head.
To assess if the moving coil is damaged, solder one end of the meter head connector with a soldering iron and take another good multimeter and set it to the R×1k range to measure its resistance.
At the same time, observe if the moving coil is deflected. If the needle is unstable, it is a local short circuit or poor contact. If the moving coil does not deflect, it means it is open circuit or blocked by foreign objects. A further inspection should be carried out.
2. Check the dc voltage and current files.
If the multimeter's dc voltage files are normal, most DC files are also generally normal.
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 the 5mA range:
If there is no indication for the 5mA range, the problem must be in the 0.5mA or 50μA range;
If the reading is too large, the error is in the 50mA or 500mA range.
3. Check the ac volts and resistance files.
Based on the normal dc volts and dc files, continue checking the ac volts and resistance files.
The errors in these two gears are usually expressed in large errors, pointer trembling, missing display and zero point setting.
In the case of an overhaul, you should first open the back cover of the multimeter in order to beobserve whether there are obvious phenomena such as component burn-out or wire desoldering, etc., and then use the circuit diagram to analyze and judge:
Large errors and no readings are generally caused by component changes in the corresponding local file, short circuit, mold;
The pointer shakes and most of the two rectifier tubes are open or the corresponding component is open;
If the Ω gear is not set to zero, it is mostly due to battery depletion, or the positive and negative electrodes of the battery are oxidized and the contact resistance increases; It can be applied with a small amount of clean lubricating oil and then rotated back and forth for a few weeks. If the oxidation is severe, it should be polished with fine sandpaper.
