Meaning of Letters on Electronic Components in Circuit Boards

Rx is a resistor. In circuit diagrams, there are many resistors, numbered sequentially, R1, R2…

Cx is a non-polar capacitor, a noise filter capacitor at the power input.

IC is an integrated circuit module.

Ux is an IC (integrated circuit component).

Kx varies by manufacturer and defines different component libraries.

Tx is a test point (for factory testing).

Spk1 is a speaker (buzzer, horn).

Qx is a transistor.

Jx is a jack (such as an audio jack).

Y1 varies by manufacturer and defines different component libraries.

Additionally, there are CEx – electrolytic capacitors, CNx – arrays of capacitors (multiple capacitors together), RNx – resistor arrays, CONx – connectors, Dx – diodes, Hx – holes, JPx – jumpers, Lx – inductors/magnetic beads, LEDx – light-emitting diodes, Xx – crystal oscillators.

Each manufacturer has its own component library, and the components used in circuit diagrams are taken from these libraries (large manufacturers). For some uncommon components, such as CON and JP, the definitions may vary by manufacturer.

R (resistor).

FS (fuse).

RTH (thermistor).

CY (Y capacitor: high-voltage ceramic capacitor, safety-rated).

CX (X capacitor: high-voltage film capacitor, safety-rated).

D (diode).

C (capacitor).

Q (transistor).

ZD (zener diode).

T (transformer).

U (IC chip).

J (jumper).

VR (variable resistor).

W (voltage regulator).

K (switching components).

Y (crystal oscillator).

On circuit boards, you often see labels like R107, C118, Q102, D202, etc. Generally, the first letter indicates the component type, such as R for resistors, C for capacitors, D for diodes, Q for transistors, etc.; the second is a number indicating the function number of the circuit, such as “1” for mainboard circuits, “2” for power circuits, etc. This is determined by the circuit designer; the third and fourth digits indicate the sequence number of similar components on that circuit board.

R117: Resistor on the mainboard, number 17.

T101: Transformer on the mainboard.

SW102: Switch.

LED101: Light-emitting diode.

LAMP: (Indicator) light.

Q104(E,B,C): Bipolar transistor, E: emitter, B: base, C: collector.

EG: “If R117 is a resistor, measuring with a multimeter should show continuity, right? Measuring resistance directly on the circuit board is not scientific; the measurement result will be smaller than the actual value, sometimes much smaller. It is best to solder out a lead for measurement.”