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SMD code M34 in SOT-23

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-23 are printed M34

Not sure which one you have?

Answer up to 4 quick questions and these 2 parts are ranked, with a meter test that settles it. It works on a dead part too.

all SOT-23, 3 pins. What differs:

  • BF861BSOT-23PhiPhi
    What it is
    JFET
    Maker
    Phi
    Package
    SOT-23
    Pins
    3
    Details
    N-channel junction FETs
    Source
    Published code list

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

    Datasheetfor BF861B, opens in a new tab
  • FN1A4PSOT-23NEC ElectronicsNEC Electronics
    What it is
    Not recorded
    Maker
    NEC Electronics
    Package
    SOT-23
    Pins
    3
    Details
    Si-pnp-Digi: Sw, 60V, 100mA, 200mW, R1/R2=10k/47k
    Source
    Published code list

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

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.

JFET

Ohms range for drain to source, diode range for the gate, part lifted.

Working, it reads

Drain to source conducts both ways at a few hundred ohms, depending on the part, and some meters beep on it. The gate reads one junction to drain and to source, about 0.6 to 0.7 V, and open the other way.

Dead, it reads

  • The gate the same both ways to drain or source, near 0 V with a continuous beep: gate shorted.
  • Drain to source open: the channel has failed open.
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:
Drain to source resistance varies from part to part. An identical part elsewhere on the board shows what is normal.
Watch for:
A good channel can beep like a short between drain and source. That is normal; the gate junction says whether it has failed.

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

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.

Codes that begin with M34

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

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