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SMD marking

R1in SOD-123F

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.

R1 on a chip resistor

0.1 Ω

0.1 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 0.1 Ω. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 0.1 Ω on the board is a fault. Open, or well above 0.1 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 0.1 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, SOT-353, SMA), R1 is a part code instead. Those parts are listed below.

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.

The only part printed R1 in this package in our tables

BZD27C180P-M

What it is
Zener diode
Maker
Vishay
Package
SOD-123F
Pins
2
Details
180 V Zener diode
Source
From the manufacturer's datasheet

Is it dead?

Diode range for the forward check, part lifted, red probe on the anode. A bench supply for the Zener voltage.

Working, it reads

About 0.6 to 0.8 V forward and open in reverse on the diode range. Its Zener voltage shows only on a supply: feed it through a resistor that sets about 5 mA, cathode to positive, read quickly, and it should hold near its rated voltage.

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, forward too: failed open.
  • Holds well off its rated voltage on the supply test: drifted.
  • A soft knee, or a voltage that creeps on the supply test: leaky.
On the board:
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 meter's diode range stops at about 2 to 3 V, so almost every Zener reads open in reverse on it, good or bad; a 3 V meter may just show a 2.4 or 2.7 V part. Above about 3 V the meter cannot tell a Zener from a plain diode.

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

Datasheetfor BZD27C180P-M, opens in a new tab

Printed with a code easy to misread

This part is printed with a character that is easy to misread as what you typed. The odd one out is marked on each.

  • BFP196printed RIRF transistor, Infineon

    Printed RI on the part. Easy to misread as R1. Check that character with a loupe before you order anything.

    What it is
    RF transistor
    Maker
    Infineon
    Package
    Not recorded
    Pins
    Not recorded
    Source
    From the manufacturer's datasheet

    Is it dead?

    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:
    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.

    Datasheetfor BFP196, opens in a new tab

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