How to Identify Circuit Board Components

All electronic equipment is made up of a number of component parts that work together, modifying and managing current and voltage in a variety of different ways. Most components are standard, off-the-shelf parts; they have distinctly identifiable shapes, sizes and colors. With a little practice you can learn to identify what the different parts are.

A schematic diagram for an electronic circuit can be a helpful guide to identifying components. In the schematic, straight solid lines indicate wiring and connections between various parts. Short zigzag lines are resistors. Capacitors are represented by short parallel lines that may be straight or curved. Transistors and diodes have arrows indicating the direction of current flow. Complex components such as integrated circuits are represented by a block diagram. Each symbol is typically labeled with a letter and a number according to a standard scheme; for example, the 11th resistor in the circuit will have the label "R11" on the schematic.

The circuit board itself is a thin plastic rectangle, usually mounted inside the equipment case. Small boards are matchbook-sized; large ones can measure 20 inches or more on a side. A typical board has components on one side and conductive copper foil paths on the other that serve as the circuit’s wiring. Boards are usually tan or blue, but also come in other colors.

Integrated circuits are miniature electronic components that may contain up to billions of microscopic transistors, resistors and other parts. Although they come in many different package styles, they generally are dark rectangular slabs of plastic or ceramic that connect to the board via several metal pins; they have a passing resemblance to small pieces of dark chocolate. ICs usually have part numbers written on them to help you identify them.

Resistors are simple electronic components that limit the amount of current passing through a circuit. On a board, resistors are small horizontal cylinders bearing four or five colored stripes; the stripes are a code that reveals the part’s resistance in ohms. For example, the color code red-red-orange-gold is a 22,000-ohm resistor accurate to 5 percent. A board may have dozens of resistors.

Capacitors serve as storage containers for electric charge, and are rated by capacitance in farads and breakdown voltage in volts. Although vintage capacitors have color codes, modern examples typically have the farad and breakdown voltage ratings printed on the part. Capacitors may be vertical or horizontal cylinders, disk-shaped or resemble glossy gumdrops.

A circuit board may have one or more connectors attached to it; a cable snaps onto the connector and carries electrical signals from it to other parts of the electronic equipment. Connectors are usually plastic and have one or more metal pins or fittings that mate with the cable.