Pointer multimeter fault repair method
There are fewer pointer multimeters in use nowadays. A digital multimeter is an instantaneous sampling style instrument. It uses 0.3 seconds to take a sample to display the measurement result. Sometimes the results of each sample are only very similar. Not exactly the same. This is not as convenient to read the results as the pointer type.
Needle multimeter internal structure is simple so the cost is low. Fewer functions. Simple maintenance. Over-current and over-voltage capability. Below we still say in detail about the pointer multimeter failure commonly used repair methods:
First, the initial identification before overhaul
Before overhaul, first of all, with a new battery in line with the requirements of the table, the multimeter set R × 1, R × 10, R × 100 or R × 1k file, the two pens shorted to see whether the needle has no indication, if there is no indication, generally is the fuse (0.5A) or the head coil open-circuit caused by. Judge whether the moving coil is damaged method is to use a soldering iron to weld open one end of the head wiring, and take a good multimeter set R × 1k file to measure its resistance, while observing whether the moving coil is deflected, if the head of the moving coil internal resistance of 0 Ω or infinity, the moving coil does not deflect, it can be judged that there is a failure of the head: 0 Ω internal resistance indicates that the moving coil is short-circuited, infinity for the open-circuit, the needle is unstable for the local short-circuit or poor contact, the moving coil does not deflection description Open circuit or stuck by foreign objects, should be further checked.
Second, overhaul DC voltage file, DC current file
In general, if the multimeter DC voltage file is normal, most of the DC current file is also normal; if the DC voltage file is not normal, most of the DC current file is also a problem, which is more common to open circuit. A more reasonable method of judgement is to start testing from the middle file, MF-30 has 50μA, 0.5mA, 5mA, 50mA, 500mA and other grades, it is appropriate to start from the 5mA file: if the 5mA file is not indicative of the problem must be in the 0.5mA or 50μA file; if the readings are large, then the fault is in the 50mA or 500mA file.
Third, overhaul the AC voltage file, resistance file
In the DC voltage file, DC current file on the basis of normal, and then further check the AC voltage file and resistance file. The fault of these two files are mostly manifested in large errors, pointer jitter, no readings and adjusted to zero. Repair, you should first open the back cover of the multimeter, observe whether there are obvious components burned or wire desoldering and other phenomena, and then analyze and judge according to the schematic diagram: error and no readings, generally corresponding to the file of the components of the value of the short circuit, local short-circuit, mould broken; pointer jitter, mostly one of the two rectifier tubes or the corresponding components are open-circuit; Omega can not be adjusted to zero, is mostly the battery is depleted, or the battery, positive and negative pole pieces of oxidation, contact resistance Increase due to; if the individual file can not be adjusted to zero (such as R × 1 file), after checking and no obvious fault, it is mostly due to increased contact resistance of the range switch, can be a small amount of clean lubricant coated with a few weeks of reciprocal rotation, oxidation of serious applications of fine sandpaper polishing.
