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WhatSMDSign in

Guides to SMD codes and parts

These guides are for the repair bench. Their examples are counted from our own tables of marking codes, and each guide links to the code pages it draws on.

Guides

  1. SMD marking codes explained

    What a marking code is, why one code fits many parts, which characters are dates or lot marks, with worked examples.

  2. Identifying an SMD transistor from its code

    Common SOT-23 transistor codes, telling a transistor from a diode pair or a MOSFET, and finding the base with a meter.

  3. Identifying an SMD diode from its code

    Finding the cathode, the four ways a SOT-23 holds one or two diodes, Zener codes by voltage, and diodes on the meter.

  4. A7 on a SOT-23: diode pair or MOSFET?

    What A7 is printed on in SOT-23, whether the letter after it matters, and three readings that tell a BAV99 from an AO3407.

  5. Part code or value code?

    Telling a value printed on a chip resistor or capacitor from a part code, and reading 104, 472, 4R7 and 01C.

  6. SMD package sizes

    Body sizes, lead counts and other names of the small packages, drawn to one scale, and measuring one without calipers.

  7. Testing SMD parts with a multimeter

    Six readings that identify a three-lead part, what each kind of part reads working and failed, and the readings that mislead.

Calculators and code lists