Characteristics of resistance damage

Resistors are the most common components in electrical equipment, but they are not the components with the highest failure rate. Resistor failures occur mostly through open circuits, with resistance increasing rarely and decreasing even less frequently. There are several types of resistors such as carbon film resistors, metal film resistors, wire-wound resistors, and fuse resistors. The first two types are the most widely used, and their failure characteristics are as follows: 

First, the failure rates of low-resistance values (below 100Ω) and high-resistance values (100kΩ) are relatively high, while very few failures occur for resistances in the range of (such as several hundred ohms to several tens of kiloohms). 

Secondly, when low-resistance resistors are damaged, they often appear charred and black, which is easily detectable. However, high-resistance resistors rarely show any signs of damage. Wire-wound resistors are used for limiting large currents and have relatively low resistance values. When cylindrical wire-wound resistors are damaged, some may turn black or have their surfaces peel off or develop cracks, while others show no signs. Cement resistors are a type of wire-wound resistors, and when they are damaged, they may break, otherwise there are no visible traces. Fuse resistors, when damaged, may have a piece of the surface blown off, while others show no traces at all, but they will never become charred or black. Based on these characteristics, during the inspection of resistors, one can focus on certain aspects to quickly identify the damaged resistors.