Editing Category:Common Issues (section)

==== Passive components ====
Resistors, capacitors, and inductors are all common ''passive'' components. This means that they are not powered, and rather are strategically placed around the schematic to create the desired effect. These components can all be diagnosed with the power OFF and your meter in resistance mode (yes, even for capacitors). You cannot probe with a meter in resistance mode while the circuit is powered{{---}}your measurements will be meaningless.

Capacitors and inductors are ''reactive'' components, as their design exploits electromagnetic properties allowing energy storage as electricity (electric fields: capacitance; electrons/charge) and magnetism (magnetic fields: inductance; magnetic flux/"magic").  Resistors are designed to avoid these reactive properties, instead to impede the flow of charge in a static, ''non-reactive'', consistent manner, limiting flow proportional to the voltage. To do so, resistors dissipate as heat the energy absorbed from the electrons flowing through, again proportional to the (the square of the) voltage.

Passive components are generally constructed of "normal" materials, classified as conductive (conductors) and non-conductive (insulators).

* '''Resistors''' (component designation R) can be used to create voltage drops and condition signals. Typically, when they fail, they will burn on the inside and either become an open circuit ("OL" on your multimeter) or short circuit (0{{nbsp}}{{ohm}}), although partial failures are possible. it is not always easy to measure the resistance in circuit because of other nearby components (like capacitors) which charge up and will distort the measurement. However, measuring them with the resistance mode should give you an idea of whether the part is in good health or not most of the time.

* '''Capacitors''' (component designation C) act as small "tanks" of energy. They can be used for a variety of things, including signal filtering, power supply decoupling (reducing ripple), and AC coupling signals. You can't measure capacitance in circuit because of the parasitic capacitance in many of the traces as well as the behavior of other components. However, this doesn't really matter because their failure mode is much more straightforward{{---}}they just get shorted. Often times, this causes a problem because they are used as power supply decoupling, meaning they are connected from the supply rail to ground{{---}}meaning a short basically dumps the power supply entirely.  They do not always appear burned or broken when failed. A trickier issue with these is that all decoupling capacitors are connected between the supply and ground, effectively putting them in parallel{{---}}meaning if there is one failure, it will appear as all of them failing (until you remove the specifically broken part). This can be tedious to track down.[[File:Inductor.png|thumb|Inductor symbol.]]

* '''Inductors''' (component designation L) are small turns of wire. They work based on the electromagnetic field produced by current flowing through the wire. Inductors are generally used power supply filtering to remove high frequency content (like in switching power supplies) and oscillator circuits. Since they literally are just turns of wire, they will look like a short on your meter. However, this also means that they generally do not change value and when they fail, they will just fail open (OL). These generally will cause you the least amount of problems.