Practical Electronics/Common Problems

it used to work, but no more
If it works once, most electronic devices will continue to work almost indefinitely. There are a few exceptions:
 * nearly every electronic component will be permanently damaged or destroyed, if power or other connections are connected to something with a voltage too large to handle, or unexpectedly reversed. Designers often put a "protection circuit" -- such as a crowbar circuit -- between connectors and sensitive components. But with adequate protection, most components will last indefinitely:;
 * transistors
 * integrated circuits
 * ceramic capacitors
 * printed circuit boards
 * Some things, even when used normally, will eventually wear out and stop working:
 * primary batteries
 * secondary batteries
 * incandescent bulbs
 * LED degradation: every LED (including the infrared LED in each opto-isolator) gradually gets dimmer and dimmer.
 * aluminum electrolytic capacitors ("wet electrolytics").
 * relays

High temperature and high current usually accelerates wear-out. Sometimes a heat sink can extend the life of a component.