Every component on a board has a reference designator: a short code made of a letter prefix and a number. R512 is a resistor, PC113 a capacitor in the power section, U23 an integrated circuit. The designator is unique on the board and identical in the schematic, the boardview and the bill of materials — which makes it the link between documents and the physical board.
Common prefixes
| Prefix | Part | Power-section variant on many designs |
|---|---|---|
| R | Resistor | PR |
| C | Capacitor | PC |
| L, FB | Inductor, ferrite bead | PL |
| D | Diode, LED | PD |
| Q | Transistor, MOSFET | PQ |
| U | Integrated circuit | PU |
| J, JP, CN | Connector, jumper | PJ |
| F | Fuse | PF |
| Y, X | Crystal | — |
| TP, T | Test point | — |
The extra P used by many ODMs for power parts helps you spot the power section quickly. Exact conventions vary between designers, so treat the table as a guide.
How designators connect your documents
- You find a part in the schematic — say, a feedback resistor
PR217. - You search
PR217in the boardview and the viewer jumps to it. - You find it on the board, confirm the label on the silkscreen if it is printed, and measure.
The same works in reverse: click a burnt part in the boardview, read its designator and search the schematic to see what it does.
Suffixes and variants
- Letter suffixes such as
PQ5AandPQ5Boften mark two halves of one dual-transistor package. The boardview may list onlyPQ5. - Option markers such as
@next to a designator indicate the part belongs to an optional configuration and may not be fitted. - Daughterboards have their own numbering, so
R12on a USB board andR12on the motherboard are different parts.
When the silkscreen does not help
Modern laptop boards are so dense that many designators are not printed at all, or are printed far from the part. That is normal and is exactly why boardviews are so useful. When you must work without one, use landmarks — connectors, large chips, inductors — and the layout hints in the schematic to narrow down the area.
Common mistakes
- Confusing similar designators like
R512andR521when copying them between documents. Copy and paste instead of retyping. - Assuming a designator from one board revision refers to the same part on another revision; positions and even numbering can change.
See also Laptop Schematic Symbols Explained for how designators appear next to symbols.