Repair of Broken Wire of Moving Coil of Instrument Head

AC and DC pointer instruments such as ammeters and voltmeters are commonly used measurement tools for electrical equipment such as motors. Once the moving coil of the meter head is disconnected, the pointer will lose power and measurement will not be possible. At this time, you may wish to use the circuit as shown in the figure for repair. Broken wires in moving coils often occur on the surface of the coil or at the lead joints. This is because the surface of the coil is in contact with the air and is easily susceptible to moisture, oxidation and mold breakage, or breakage due to collision. You can weld the outer end of the hairspring inside the meter head, take out the moving coil, take a four-fold magnifying glass, and check that there are no obvious mechanical scratches, then you can connect the wires as shown in Figure (a). Use a test lead to intermittently touch the terminal of the coil hairspring holder. Note that each contact should not exceed 1/25 seconds. As long as you find a spark between the watch needle and the terminal of the hairspring holder and the light bulb flashes at the same time, it means that the coil disconnection has been connected. At this time, take a multimeter (set to R×100) and measure the coil as shown in Figure (b). If there is resistance (it should be the same as the original resistance), it is considered repaired.