Every part on a laptop board has a name: a short code of letters and numbers called a reference designator. It is the link between the schematic, the boardview and the physical board. Once you can read the letters, a designator tells you what kind of part you are looking at, which section of the board it belongs to and often which schematic page to open. This guide decodes the designators you meet on laptop boards, including the power-section prefixes that confuse many beginners.
The basic letters
| Letter(s) | Part type |
|---|---|
| R | Resistor |
| RN, RP, RA | Resistor network (array) |
| C | Capacitor |
| L | Inductor or ferrite bead |
| FB | Ferrite bead (on some boards) |
| D | Diode, LED, TVS diode |
| Q | Transistor or MOSFET |
| U | Integrated circuit |
| F | Fuse |
| Y, X | Crystal or oscillator |
| J, JP, CN, CON | Connector |
| SW | Switch |
| T | Transformer (rare on laptops); on some boards a test point |
| TP, PAD | Test point |
| H | Mounting hole |
The general idea is described in the glossary under reference designator.
The P prefix: power section
Many board designers — particularly Compal, LCFC, Quanta and others — add a P in front of the designators of parts in the power section:
| Designator | Meaning |
|---|---|
| PU | IC in the power section (charger, regulator controller) |
| PQ | MOSFET or transistor in the power section |
| PR | Resistor in the power section |
| PC | Capacitor in the power section |
| PL | Inductor in the power section |
| PD | Diode in the power section |
| PJ | Jumper in the power section — solder pads or a zero-ohm link |
| PF | Fuse in the power section |
This is useful at a glance: a PQ near the DC jack is part of the input or charging circuit; a PL next to the processor is a core regulator inductor. Power-section parts are also where most board faults are found.
Jumpers (PJ)
PJ positions deserve special mention. They are often two pads bridged with solder or a zero-ohm part, placed where a rail can be split. They exist partly for factory testing — and they are ideal places to split a rail when hunting a short.
How the numbers are assigned
Designators are usually numbered by schematic page or by area:
- On many schematics, parts on page 45 are numbered in the 4500 range, or parts on the charger page share a common prefix number.
- Some designers number by board area instead.
Either way, consecutive numbers often sit on the same page. When you find PR501 in the boardview, PR502 and PR503 are probably on the same page and in the same circuit. Learning a schematic's numbering convention speeds up navigation enormously.
Not-fitted parts
Schematics show parts that are not fitted on every board variant. Common conventions:
- a note such as @, X, NI, DNI, NC or DNP beside the part;
- a different font or a crossed-out symbol;
- a table of variants listing which positions are fitted.
On the board, a not-fitted position is simply an empty footprint. Treat missing parts carefully: an empty footprint may be intentional, or the part may have been knocked off. The schematic's markings tell you which. This is covered in detail in Unpopulated Components (NC, DNI, @) in Laptop Schematics.
Test points
Test points carry designators such as TP123, PAD45 or T12. In the boardview they are usually round pads; in the schematic they appear as small circles on a net. They are among the best places to measure, as described under test point.
Using designators in the boardview
The boardview's search function finds any part by designator:
- search PU to list all power ICs and see where they sit;
- search F or PF to find all fuses;
- search PJ to find every rail-splitting jumper;
- search a specific designator from the schematic to locate it instantly.
Search techniques are covered in Finding Component Locations Fast with Boardview Search.
Using designators in the schematic
In a PDF schematic, search for the designator to find the page it is on. If the schematic was printed to PDF from the design tool, text search works; if it was scanned, it may not. Where search fails, the numbering convention helps you jump to the right section.
Designators on the board itself
Older and lower-density boards print designators in the silkscreen next to parts. Modern laptop boards are too dense for that; most designators appear only in the boardview. Occasionally you will see designators for large parts and connectors only. Symbols used alongside designators are explained in Laptop Schematic Symbols Explained.
Different designers, different habits
| Habit | Where you might see it |
|---|---|
| P prefix for power parts | Many ODM designs |
| Numbers grouped by schematic page | Many ODM designs |
| FB for ferrite beads, L for inductors | Some designs; others use L for both |
| JP for jumpers and connectors alike | Some designs |
| Apple-style designators with different numbering | Apple boards |
Always check one or two parts against the schematic when starting on a new manufacturer's board.
Writing designators into your notes
When you record a repair, write the designators as well as the description: "PQ3 shorted drain–source" or "PC512 cracked, 22 µF 0603" is far more useful the next time than "a MOSFET near the charger". Designators are stable for a board design and revision, so notes keyed to them let you go straight to the same part on the next board with the same code. Add the revision, because designators can move between revisions.
When designators do not match
Occasionally the boardview and schematic disagree about a designator, or a board revision has renumbered parts. Signs include a designator that points to the wrong type of part, or a part that exists on the board but not in the documents. In those cases, trust the net connections over the names: a part connected between the same two nets as in the schematic is the same part, whatever it is called.
Example: following designators through a charger fault
A laptop does not charge. The schematic's charger page shows PU1 (the charger IC), PQ1 and PQ2 (input MOSFETs), PQ3 (battery MOSFET), PR1 and PR2 (sense resistors) and PL1 (the charging inductor). In the boardview, a search for PU1 finds the charger next to the DC jack, and the other parts cluster around it with numbers close to its own. Measuring in order — input at PQ1, output at PQ2, sense voltage across PR1, gate drive to PQ3 — finds PR2 cracked. The designators turned a dense corner of the board into a short, ordered list.
FAQ
What does the P in PU or PQ mean?
On many boards it marks parts in the power section: power IC, power MOSFET and so on.
Why are designators not printed on the board?
Modern boards are too dense. Use the boardview to find them.
What does @ next to a part mean?
On many schematics it marks a part that is not fitted on all variants. Check the schematic's legend.
Why do numbers jump between pages?
Many designers number parts by page, so each page has its own range.
Is PJ a jumper or a connector?
In the power section it is usually a jumper — pads or a zero-ohm link that can split a rail.
Bottom line
Reference designators tie the schematic, the boardview and the board together. Learn the letters, recognise the P prefix for power parts, use the page-based numbering to navigate, respect not-fitted markings, and use the boardview's search to go from a designator to the physical part in seconds.