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WhatSMDSign in

SMD code U

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.

12 parts are printed U

Not sure which one you have?

Answer up to 4 quick questions and these 12 parts are ranked, with a meter test that settles it. It works on a dead part too.

  • AOZ8S321UD4-03ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Details
    ESD protection for high-speed interfaces
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8S321UD4-03, opens in a new tab
  • AOZ8S321UD4-05ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Details
    ESD protection for high-speed interfaces
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8S321UD4-05, opens in a new tab
  • AOZ8S507BDS-07ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8S507BDS-07, opens in a new tab
  • AOZ8S530BLS-05ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8S530BLS-05, opens in a new tab
  • AOZ8310ADI-04ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8310ADI-04, opens in a new tab
  • AOZ8851ADI-18ESD protection diode, Alpha & Omega Semiconductor
    What it is
    ESD protection diode
    Maker
    Alpha & Omega Semiconductor
    Package
    Not recorded
    Pins
    Not recorded
    Details
    ESD protection for high-speed interfaces
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor AOZ8851ADI-18, opens in a new tab
  • BAR88-02VPIN diode, Infineon
    What it is
    PIN diode
    Maker
    Infineon
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: PIN diode or varicap.

    Datasheetfor BAR88-02V, opens in a new tab
  • BB545Infineon
    What it is
    Not recorded
    Maker
    Infineon
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

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

    Datasheetfor BB545, opens in a new tab
  • IRLML6344N-channel MOSFET, Infineon
    What it is
    N-channel MOSFET
    Maker
    Infineon
    Package
    Not recorded
    Pins
    Not recorded
    Details
    30V Single N-Channel StrongIRFET™ Power MOSFET in a SOT-23 package
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: N-channel MOSFET.

    Datasheetfor IRLML6344, opens in a new tab
  • PESD3V3Z1BSFESD protection diode, 2 pins, Nexperia
    What it is
    ESD protection diode
    Maker
    Nexperia
    Package
    Not recorded
    Pins
    2
    Details
    Extremely low capacitance bidirectional ESD protection diode
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor PESD3V3Z1BSF, opens in a new tab
  • PESD4V0Z1BSFESD protection diode, 2 pins, Nexperia
    What it is
    ESD protection diode
    Maker
    Nexperia
    Package
    Not recorded
    Pins
    2
    Details
    Extremely low capacitance bidirectional ESD protection diode
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor PESD4V0Z1BSF, opens in a new tab
  • VCUT07B1-HD1ESD protection diode, Vishay
    What it is
    ESD protection diode
    Maker
    Vishay
    Package
    Not recorded
    Pins
    Not recorded
    Details
    Bidirectional Symmetrical (BiSy) Single Line ESD Protection Diode in LLP1006-2L
    Source
    From the manufacturer's datasheet

    Is it dead? The meter test is below: TVS or ESD protection diode.

    Datasheetfor VCUT07B1-HD1, 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.

TVS or ESD protection diode

Diode range, from the protected line to ground, part lifted if you can.

Working, it reads

A one-way part reads about 0.6 to 0.8 V forward and open in reverse. A two-way part reads open both ways. Arrays with several lines read as the datasheet's diagram draws them.

Dead, it reads

  • From the line to ground, the same reading both ways, near 0 V with a continuous beep: shorted.
  • A reading both ways on a one-way part: leaky.
  • A one-way part open both ways: failed open.
On the board
, a line reading shorted to ground can be this part or anything else on that line. Lift it: if the short goes with it, it has failed.
Compare:
The same part on the next line or connector pin is the healthy reading to compare with.
Watch for:
A two-way part reads open both ways when it is good, exactly like one that has failed open. The meter cannot tell them apart; an identical part on the next line can.

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

PIN diode or varicap

Diode range, part lifted or one leg off the pad. Red probe on the anode.

Working, it reads

About 0.6 to 0.9 V anode to cathode, and open the other way.

Dead, it reads

  • The same reading both ways round, near 0 V with a continuous beep or the same middling value: shorted.
  • Open both ways: 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:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
Watch for:
A varicap that has drifted in capacitance reads normal on a meter. Only a capacitance meter or the tuning itself shows it.

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.

N-channel MOSFET

Diode range, part lifted. Test drain to source first, then short gate to source and test again.

Working, it reads

Red probe on the source, black on the drain: about 0.4 to 0.9 V, the body diode. Open the other way. The gate reads open to both other pins, both ways.

Dead, it reads

  • Drain to source the same both ways, near 0 V with a continuous beep, and still so after shorting gate to source: shorted. The classic failure.
  • The gate reads low to source or drain: gate shorted. Often all three pins end up shorted together.
  • No body diode at all: failed open.
On the board
the gate usually has a resistor to the source, so gate to source reads that resistor, which is not a fault. A drain short can be the load. Lift a leg to be sure.
Compare:
If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
Watch for:
The diode range can charge the gate enough to turn the part on, and then drain to source reads near 0 both ways on a good part. Short gate to source and test again before you condemn it.

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 U

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

Codes not listed here are printed on 71 more parts.

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