The electric barrier of the pointer multimeter is broken, and other gears can be used, indicating that the 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 burning current block with several small resistance wire wound resistors when the DC current block is pulled out (no matter what type of pointer multimeter, they are all wire wound resistors, and they are all made of constantan. The resistance wire is wound, and the resistance value is very small, for example, there are 4 resistances in the MF-47 type, which are 0.54Ω, 5.4Ω, 54Ω, 540Ω). But what the proprietor said is that the multimeter has only a problem with the electrical barrier, so there is no problem that occurs in this gear.

The second reason is; for beginners electronics and electricians, after using the multimeter's electric blocking measuring element or checking the circuit, they did not turn the gear of the multimeter to the AC 500V gear, and then plugged in the 220V AC line or socket. caused by alternating current in the test. There are many models and manufacturers of commonly used pointer multimeters. The most common and widely used ones are the old-fashioned 500 and MF-47 multimeters produced in Nanjing.

①MF{{0}} multimeter has a DC current gear (DCA), a total of five common gears plus a 5A high current expansion jack, 0~0.05mA~0.5mA~5mA-50mA~500mA.

②It has eight commonly used gears for direct current voltage (DCV) plus an extension jack that can measure DC2500V. 0~0.25V~1V~2.5V~10V~50V~250V~500V~1000V~2500V.

③There are six gears of AC voltage (ACV), 0~10V~50V~250V~500V~2500.

④ Its DC blocking (Ω) five gears. 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 give a prompt sound). Due to limited space, functions such as transistor DC amplification factor hFE, infrared remote control emission signal detection, and audio level DB are omitted.

First of all, when measuring electrical resistance, insert the black test lead into a hole → the negative pole of the meter head → 20.2Ω resistor, 220.4Ω resistor, and 2430Ω resistor, all of which are in parallel with the meter head. At this time, the red test lead is inserted into the ten jack of the multimeter, passes through a 1A insurance tube → 1.5V dry battery is connected in series with the resistor, and then passes through a 20k resistor → 1..7k resistor to block the zero adjustment variable potentiometer → a 500Ω resistor →The other meter is calibrated R plus →the positive pole of the meter is plus . It is easy to understand the closed loop. According to personal experience, you can search for it.

Use another multimeter to find and measure these resistances. Generally, this kind of fault will only burn the resistance of the resistance that was used at that time. These resistors are non-standard value resistors, which can be connected in series with damaged resistors or replaced by a piece of constantan resistance wire wound by itself. The constantan wire can be intercepted from a wire-wound variable potentiometer.