The first two kinds of resistors are the most widely used. The characteristics of their damage are as follows: first, the damage rate of low resistance (below 100 Ω) and high resistance (above 100k Ω) is high, and the middle resistance (such as hundreds to tens of thousands of Ω) is rarely damaged; second, when the low resistance resistance is damaged, it is often scorched and blackened, which is easy to find, while when the high resistance is damaged, there is little trace.
Wire wound resistance is generally used for large current limiting, and the resistance value is not large. When the cylindrical wound resistance is burnt out, some will be blackened or the surface will be cracked, some will not have any trace. Cement resistance is a kind of wire wound resistance, which may break when burned out, otherwise there is no visible trace. When the safety resistor is burnt out, some surfaces will blow off a piece of skin, and some have no traces, but they will never scorch and blacken. According to the above characteristics, when checking the resistance, we can focus on it and quickly find out the damaged resistance.
According to the characteristics listed above, we can first observe whether the low resistance on the circuit board is blackened, and then according to the characteristics of most open circuit or larger resistance when the resistance is damaged, and the high resistance is easy to be damaged, we can use the multimeter to directly measure the resistance at both ends of the resistance with high resistance on the circuit board. If the resistance is larger than the nominal resistance, it will be better If the measured resistance is smaller than the nominal resistance, it is generally ignored. In this way, every resistor on the circuit board is measured once. Even if one thousand resistors are killed by mistake, one resistor will not be missed.