Repair Tips for Burnt Components in the Multimeter Resistance Range
It is common for the resistance range of a multimeter to burn out due to incorrect range selection.
Taking the R × 1 range of the U-10 multimeter as an example, its simplified circuit is shown in Figure 5-22.
Here, R5 is the resistance zeroing potentiometer, R16 is the shunt resistor for the R × 1 range, and the center value of the ohms for this range is 10 Ω. The main cause of the malfunction is the misuse of the R × 1 gear to measure the mains power, resulting in the burning of R16. There are two methods to repair the shunt resistor:
The first method: Take a manganese copper wire approximately 1m long and 1-1mm in diameter and wrap it around the rubberwood frame. When there is no rubberwood skeleton, a resistor with tens of k Ω and 1/2W can also be used as a substitute. Use a high-precision multimeter, such as the MF18 type, to measure the resistance of manganese copper wire. Select a section of 40 Ω± 0.4 Ω and wrap it around a rubberwood frame or resistor. Weld the two leads together and replace them. Of course, it is best to use a digital multimeter or bridge to measure the resistance of the manganese copper wire, which is more accurate. If you don't have manganese copper wire on hand, you can replace it with a wire wound resistor or a 20W waste soldering iron core by removing the heating wire. But the temperature stability of electric heating wires is poor. To prevent short circuits between turns during winding, wiring grooves can be filed on the rubberwood frame.
The second method is to use two 20 Ω, 1/4W metal film resistors in series as substitutes for R16. The resistance error should be less than 1%.
