What may be the reason why the resistance range of a mechanical multimeter is broken?
If the resistance setting of the mechanical multimeter or pointer multimeter is damaged, but other settings can be tested normally, it means that the meter head should not be affected. According to the testing principle of the resistance range of the multimeter, it is most likely caused by the precision resistor of the resistance range being burnt out or the resistance value changing. The most likely cause of damage to the resistance profile of a mechanical multimeter is that the resistance profile is used as a voltage profile to test voltage. Therefore, before each test, you must first check whether the gear is selected correctly and develop good testing habits.
If the electrical barrier of the analog multimeter is broken and other gears can be used, it means that the meter head of the multimeter is good. This is caused by incorrect use. There are two reasons for this. One is to measure the AC220V voltage and burn several small resistance wirewound resistors in the current block when the DC current block is pulled out (no matter what model of pointer multimeter, they are all wirewound resistors, and they are all made of constantan It is made of resistance wire, and the resistance values are very small. For example, there are 4 resistors in the MF-47 type, which are 0.54Ω 5.4Ω 54Ω 540Ω). However, the leader said that the multimeter only has a problem with the electrical barrier, so the problem does not occur in this gear.
The second reason is that for beginner electronics and electricians, after using the electrical barrier measuring element of the multimeter or checking the circuit, they did not set the multimeter to the AC 500V gear, and then connected the 220V AC line or jack. Caused by AC power during testing. There are many commonly used analog multimeter models and manufacturers. The most common and widely used ones are the old-fashioned 500 type and the MF-47 type multimeter produced in Nanjing.
①The MF-47 multimeter has a DC current level (DCA), with a total of five common gears plus a 5A high current expansion jack, 0~0.05mA~0.5mA~5mA-50mA~500mA.
② It has eight commonly used gears for direct current voltage (DCV) plus an expansion jack that can measure DC2500V. 0~0.25V~1V~2.5V~10V~50V~250V~500V~1000V~2500V.
③There are six AC voltage levels, 0~10V~50V~250V~500V~2500.
④Its DC blocking (Ω) has five levels. R×1Ω R×10Ω R×100Ω Rx1KΩ R×10KΩ There is also a road buzzer during measurement (when the line resistance value is 3~10Ω, the buzzer will sound). Due to limited space, functions such as the transistor DC amplification factor hFE, infrared remote control emission signal detection, and audio level DB are omitted.
First, when measuring electrical resistance, insert the black test lead into a hole → the negative electrode of the meter → 20.2Ω resistance, 220.4Ω resistance, and 2430Ω resistance, which are all connected in parallel with the meter. At this time, the red test lead is inserted into the tenth jack of the multimeter and passes through a 1A fuse → 1.5V dry battery and resistor in series and then through a 20k resistor → 1..7k electrical barrier zeroing variable potentiometer → a 500Ω resistor → Calibrate the other meter to R+ → the positive + sign of the meter. It will be easier once you understand the closed loop. Based on personal experience, you can follow the clues to find it.
Use another multimeter to find and measure these resistances. Generally, this kind of fault will only burn the resistance of the electrical blocking bit used at the time. These resistors are non-standard value resistors. You can find a damaged resistor and connect them in series, or replace it with a piece of constantan resistance wire wound around a resistor. The constantan wire can be cut from a wire-wound variable potentiometer.
