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SMD code 31

Marking codes are not standardised, and the same code is reused by unrelated makers for unrelated parts. Below is every part in our tables printed with it, and any printed with a code that is easy to misread as it, from the manufacturers' own marking tables.

4 parts are printed 31

Not sure which one you have?

Answer up to 4 quick questions and these 4 parts are ranked, with a meter test that settles it. It works on a dead part too.

  • PDTA143XTSOT-23Digital transistor (PNP, resistors built in), 3 pins, Nexperia
    What it is
    Digital transistor (PNP, resistors built in)
    Maker
    Nexperia
    Package
    SOT-23
    Pins
    3
    Details
    50 V, 100 mA PNP resistor-equipped transistor; R1 = 4.7 kΩ, R2 = 10 kΩ
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: Digital transistor.

    Datasheetfor PDTA143XT, opens in a new tab
  • PUMD13SOT-363Digital transistor (PNP, resistors built in), 6 pins, Nexperia
    What it is
    Digital transistor (PNP, resistors built in)
    Maker
    Nexperia
    Package
    SOT-363
    Pins
    6
    Details
    50 V, 100 mA NPN/PNP resistor-equipped double transistor; R1 = 4.7 kΩ, R2 = 47 kΩ
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: Digital transistor.

    Datasheetfor PUMD13, opens in a new tab
  • TS331CX5SOT-23-5Comparator, 5 pins, Taiwan Semiconductor
    What it is
    Comparator
    Maker
    Taiwan Semiconductor
    Package
    SOT-23-5
    Pins
    5
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: Integrated circuit.

    Datasheetfor TS331CX5, opens in a new tab
  • EIA-96:310603Precision resistor (EIA-96 code), 2 pins
    What it is
    Precision resistor (EIA-96 code)
    Maker
    Not recorded
    Package
    0603
    Pins
    2
    Details
    EIA-96 precision chip resistor, significand 20.5; the printed mark adds a multiplier letter (31A = 205 Ohm, 31B = 2.05 kOhm)
    Source
    Added by hand from a published table

    Is it dead? The meter test is below: Resistor.

    Datasheetfor EIA-96:31, opens in a new tab

Is it dead? One meter test per kind

Parts of the same kind are tested the same way, so each test is here once. Each part above points to its own.

Digital transistor

Ohms range, part lifted. The datasheet gives the built-in resistors: R1 in series with the base, R2 from base to emitter.

Working, it reads

Base to emitter reads about R1 plus R2 either way round, about 20 kΩ on a 10 k and 10 k part, give or take their wide tolerance. Collector to emitter reads open. A part with no R2 reads a junction behind R1 one way instead.

Dead, it reads

  • Collector to emitter the same both ways, near 0 Ω with a continuous beep: shorted.
  • From the base, open or far above R1 plus R2: R1 has failed. Static damage shows here most often.
  • Base to emitter near 0 Ω: failed short.
On the board
this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
Compare:
The readings depend on the resistor values, so an identical part elsewhere on the board is the surest reference. Measure it the same way.
Watch for:
On the diode range a good part with 10 kΩ resistors reads open on every pair, so a good part looks dead there. Use the ohms range.

A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.

Integrated circuit

Voltage with the board powered; ohms from each pin to ground with it off.

Working, it reads

Supply pin at its voltage and the output doing what the datasheet says. Readings between pins depend on the part.

Dead, it reads

  • A pin near 0 Ω to ground or to the supply pin where an identical part does not read that: failed short.
  • Supply present, output stuck: failed, or its load has.
On the board:
A pin shorted to ground on the board can be anything on that net. Lift the pin to be sure.
Compare:
The surest reference is the same IC on a working board, measured pin by pin.
Watch for:
Its protection diodes can read like junctions between pins, even like a transistor. That proves nothing either way.

A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.

Resistor

Ohms range, across it, power off.

Working, it reads

Its marked value, within tolerance. On the board it reads the same or lower, because everything around it sits in parallel.

Dead, it reads

  • Open: burnt, cracked, or eaten through by sulphur. The commonest failure.
  • Well above its marked value: drifted high.
  • On the board, clearly higher than its marked value: it has failed, since the board can only pull a reading down.
On the board:
A reading lower than marked on the board proves nothing; lift one end. A reading higher than marked is a fault even on the board.
Compare:
The same position on another channel usually carries the same value, and so does the matching part on another board.
Watch for:
A burnt resistor usually means the part it feeds pulled too much. Find that before fitting a new one, or it burns too. The marking, not the reading, says what to fit.

A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.

Printed with a code easy to misread as 31

One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.

Codes that begin with 31

For a marking with its end worn or burnt off. Each code has a page of its own.

Open this in the search to correct a character or try another package.