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SMD code U4F

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.

U4F is a capacitor marking

0.4 µF

0.4 µF capacitor

The value is printed in full: 0.4 µF.

Check it with a meter

Lift one end and measure it on a capacitance range. A good one reads close to 0.4 µF. In circuit the meter also sees everything connected across it, so the reading means little until it is out. A failed one usually reads near 0 Ω, or a steady low resistance, on the ohms range, often from a crack. On the board a shorted capacitor shorts its whole rail. A failed reading does not change what to fit: the marking still says 0.4 µF.

On a transistor or diode body (SMA, SOT-23), U4F is a part code instead. Those parts are listed below.

3 parts are printed U4F

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.

  • MURA130SMASchottky diode, 2 pins, onsemiSchottky diodeSMA2 pinsonsemi
    What it is
    Schottky diode
    Maker
    onsemi
    Package
    SMA
    Pins
    2
    Details
    Si-diode: Schottky, U-Fast Rect, 300V, 1A, Vf<0,8V(1A), <65ns
    Source
    Published code list

    Is it dead? The meter test is below: Schottky diode.

  • UM36550SSOT-23LDO regulator, 3 pins, Union SemiconductorLDO regulatorSOT-233 pinsUnion Semiconductor
    What it is
    LDO regulator
    Maker
    Union Semiconductor
    Package
    SOT-23
    Pins
    3
    Details
    Linear voltage regulator IC: LDO, 5.0V±2%, 300mA
    Source
    Published code list

    Is it dead? The meter test is below: Voltage regulator.

  • 1 more part has no package on record
    • S-8333CCBC-I8T18 pins, ABLICNot recordedNot recorded8 pinsABLIC
      What it is
      Not recorded
      Maker
      ABLIC
      Package
      Not recorded
      Pins
      8
      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.

Schottky diode

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

Working, it reads

About 0.15 to 0.45 V anode to cathode, roughly half a silicon diode, 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.
  • A reading the wrong way round as well: leaky.
  • 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 large Schottky can read about 0.1 V forward and beep like a short, and leaks a little the wrong way when good, more when warm. It is shorted only if it reads the same both ways. Measure it cold, beside an identical cold one.

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.

Voltage regulator

Voltage, board powered, black probe on ground. Then ohms with the power off.

Working, it reads

Input pin at the supply, output pin at its rated voltage, and the enable pin high if it has one.

Dead, it reads

  • Output equal to the input: the pass element has shorted. Everything after it may have taken the full input.
  • Input present, enable high, no output: failed open, or holding itself off into a shorted load. Power off and measure output to ground.
  • Power off, input to output near 0 Ω: shorted.
On the board:
An output at 0 V is often a shorted load with the regulator in current limit. Lift the output pin: if the short stays on the board, the regulator may be fine.
Compare:
The same regulator on another rail or another board shows the right voltages and the right resistances.
Watch for:
Makers put input, output and ground on different pins in the same package, so take them from this part's datasheet. Diode or ohms readings between its pins say little; check it powered.

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

Did you find your part?

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