Finding parts in a schematic PDF

What reference designators (R1, C3, U2) mean, how to read value notation (4k7, 104, 10uF/16V), multi-unit parts, and how to find parts and turn them into a list with Schematic Viewer.

Last updated: 2026-10-09

Repairs and reviews constantly raise questions like "where is C37 on this drawing?" or "how many 10k resistors are on this board?". Ctrl+F in a PDF reader gets you part of the way; knowing the naming rules and value notation gets you there much faster.

Reading reference designators

Every part on a schematic carries a letter prefix for its type plus a number. The same reference appears on the PCB silkscreen and in the bill of materials (BOM), so it is the key that ties drawing, board and BOM together. Common prefixes (they vary a little between companies and CAD tools):

Numbers usually run from the top left of the sheet, but many designs reserve a hundred per block (C101… for the power supply, C201… for communications). The number range tells you roughly which block a part is in.

Multi-unit parts

When one chip holds several identical functions — the LM358 has two op-amps — each is drawn separately with a suffix: U4A, U4B, sometimes U4C for the power pins. Schematic Viewer groups these units into one part, U4, in the list.

Reading values

• Resistors: 4k7 is 4.7 kΩ, 1M is 1 MΩ, 0R is 0 Ω (a jumper). Using the unit letter as the decimal point keeps values legible when print smudges. A size is often appended, as in /R0402.
• Capacitors: three digits such as 104 mean the first two digits × 10 to the power of the third, in pF: 104 = 10 × 10⁴ pF = 100 nF = 0.1 µF. Voltage ratings are often added, as in 10uF/16V.
• Tolerance and dielectric: 1%, X5R, C0G and the like. When replacing a part, match these and the package size, not just the value.
• DNP / NC: "do not populate" / "no connect" — a footprint left empty on the board.

Finding them with Schematic Viewer

1. By reference: type C37. The exact C37 comes before look-alikes such as C370, and the view jumps there without pressing Enter. Or pick C37 in the Parts tab.
2. By value: search 10k or 104 to mark every place that value is written; the count in the search bar gives a rough number of parts with that value.
3. On the drawing: click a reference on the drawing to select the part; the list switches to the Parts tab.
4. As a list: save references, values and pages with Parts CSV, then sort by value in a spreadsheet for a quick BOM.

When a value is missing or different

Schematic Viewer groups value text written near a reference in the same direction. A value far from its reference, rotated differently or split over lines may not be grouped and is left empty; click the part and check the drawing. When the PDF itself carries part data — as OrCAD PDFs do — that data is used first.

A CSV made this way reflects what is drawn, so it does not replace the official BOM. Use the CAD-generated BOM for purchasing and production, and this list for reviewing and cross-checking. If the symbols themselves are new to you, see Reading schematics and datasheets.