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SMD code R3J

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.

R3J is a resistor marking

0.3 Ω

0.3 Ω resistor, 5%

The R stands in for the decimal point, which is how sub-ohm and fractional values are printed. J is the tolerance, ±5%. The same marking also reads as 0.3 µH on an inductor, and nothing in the code says which; the body of the part does.

Other readings of the same characters, most likely first

  • 0.3 µH inductor, 5%

Check it with a meter

Lift one end and measure across it. A good one reads 0.3 Ω within 5%. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 0.3 Ω on the board is a fault. Open, or well above 0.3 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 0.3 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, SMB, SMBF), R3J is a part code instead. Those parts are listed below.

4 parts are printed R3J

Not sure which one you have?

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

  • CD214B-R3600SMBRectifier, 2 pins, BournsRectifierSMB2 pinsBourns
    What it is
    Rectifier
    Maker
    Bourns
    Package
    SMB
    Pins
    2
    Details
    Diode: Rectifier, Fast, 600V, 3A, Vf<1V(3A), 40pF
    Source
    Published code list

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

  • CD214C-R3600SMCRectifier, 2 pins, BournsRectifierSMC2 pinsBourns
    What it is
    Rectifier
    Maker
    Bourns
    Package
    SMC
    Pins
    2
    Details
    Diode: Rectifier, Fast, 600V, 3A, Vf<1.15V(3A), 40pF
    Source
    Published code list

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

  • CM7R250-39A-TSOT-23LDO regulator, 3 pins, Canaan MicroelectronicsLDO regulatorSOT-233 pinsCanaan Microelectronics
    What it is
    LDO regulator
    Maker
    Canaan Microelectronics
    Package
    SOT-23
    Pins
    3
    Details
    Linear voltage regulator IC: LDO, 3.95V±2%, 150mA
    Source
    Published code list

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

  • S-8211EAJ-M5T1USOT-23-55 pins, ABLICNot recordedSOT-23-55 pinsABLIC
    What it is
    Not recorded
    Maker
    ABLIC
    Package
    SOT-23-5
    Pins
    5
    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.

Silicon diode

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

Working, it reads

About 0.5 to 0.8 V anode to cathode, and open the other way. Small switching diodes read about 0.6 to 0.7 V; large rectifiers can read a little lower.

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.
  • A reading the wrong way round as well: 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 three-pin body can hold two diodes. With a common pin they read two junctions from that pin, just like a transistor; in series they read two drops end to end. Test each pair the datasheet names.

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.

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 R3J

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

Did you find your part?

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