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SMD code R54 in USP-6C

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.

R54 on a chip resistor

0.54 Ω

0.54 Ω resistor

The R stands in for the decimal point, which is how sub-ohm and fractional values are printed.

Check it with a meter

Lift one end and measure across it. A good one reads 0.54 Ω. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 0.54 Ω on the board is a fault. Open, or well above 0.54 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 0.54 Ω. A burnt resistor usually means the part it feeds drew too much, so find that before fitting a new one.

On a transistor or diode body (SOT-23-5, SOT-23, SOT-89), R54 is a part code instead. Those parts are listed below.

2 parts in USP-6C are printed R54

Not sure which one you have?

Answer up to 4 quick questions and these 5 parts are ranked, with a meter test that settles it. It works on a dead part too.

  • IXD1421AB54ER-GUSP-6CLDO regulator, IXYSLDO regulatorIXYS
    What it is
    LDO regulator
    Maker
    IXYS
    Package
    USP-6C
    Pins
    6
    Details
    Linear voltage regulator IC: LDO, Dual out, Vo1/Vo2=3.00V±1%/2.80V±1%, 300mA, +CE
    Source
    Published code list

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

  • XC6421AB54ER-GUSP-6CLDO regulator, TorexLDO regulatorTorex
    What it is
    LDO regulator
    Maker
    Torex
    Package
    USP-6C
    Pins
    6
    Details
    Linear voltage regulator IC: LDO, Dual out, Vo1/Vo2=3.00V±1%/2.80V±1%, 300mA, +CE
    Source
    Published code list

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

  • 3 more parts have no package on record. Nothing rules them out, so they stay.
    • 2SC5750RF transistor, NEC ElectronicsRF transistorNEC Electronics
      What it is
      RF transistor
      Maker
      NEC Electronics
      Package
      Not recorded
      Pins
      Not recorded
      Details
      NPN transistor: RF, 9V, 50mA, 200mW, B=75..150, 15GHz
      Source
      Published code list

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

    • 2SC5751RF transistor, NEC ElectronicsRF transistorNEC Electronics
      What it is
      RF transistor
      Maker
      NEC Electronics
      Package
      Not recorded
      Pins
      Not recorded
      Details
      NPN transistor: RF, 9V, 50mA, 205mW, B=75..150, 15GHz
      Source
      Published code list

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

    • NE677M04RF transistor, NEC ElectronicsRF transistorNEC Electronics
      What it is
      RF transistor
      Maker
      NEC Electronics
      Package
      Not recorded
      Pins
      Not recorded
      Details
      NPN transistor: RF, 9V, 50mA, 205mW, B=75..150, 15GHz
      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.

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.

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.

Did you find your part?

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