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SMD code T77 in SOT-323

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 and published code lists.

2 parts in SOT-323 are printed T77

Not sure which one you have?

Answer up to 4 quick questions and these 3 parts are ranked, with a meter test that settles it. It works on a dead part too.

  • 2SC4571T77SOT-323RenesasNot recordedRenesas
    What it is
    Not recorded
    Maker
    Renesas
    Package
    SOT-323
    Pins
    3
    Source
    Published code list

    Is it dead? The meter test is below: This part.

  • PDTA124XUSOT-323Digital transistor (PNP, resistors built in), NXPDigital transistor (PNP, resistors built in)NXP
    What it is
    Digital transistor (PNP, resistors built in)
    Maker
    NXP
    Package
    SOT-323
    Pins
    3
    Details
    PNP resistor-equipped transistor; R1 = 22 kΩ, R2 = 47 kΩ
    Source
    Published code list

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

    Datasheetfor PDTA124XU, opens in a new tab
  • 1 more part has no package on record. Nothing rules it out, so it stays.
    • uPA804T-GBNEC ElectronicsNot recordedNEC Electronics
      What it is
      Not recorded
      Maker
      NEC Electronics
      Package
      Not recorded
      Pins
      Not recorded
      Details
      NPN transistor: Dual, VHF/UHF, 20V, 60mA, 120mW, 5GHz, B=100..200
      Source
      Published code list

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

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.

This part

Diode range and ohms range, part lifted.

Working, it reads

Depends on what it is. The datasheet, or an identical part, says.

Dead, it reads

  • Between two pins, the same reading both ways, near 0 V with a continuous beep: shorted.
  • Open between every pair of pins: failed open, or a part that reads open when working.
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:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.

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

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.

Bipolar transistor

Diode range, part lifted or its base leg off the pad.

Working, it reads

From the base, one probe colour reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.

Dead, it reads

  • Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
  • The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
  • Only one junction reads, or none: a junction has failed open. It then looks like a diode.
  • A reading the wrong way round, where it should be open: leaky.
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:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
Watch for:
A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.

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 T77

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

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