Skip to content
WhatSMDSign in

SMD code R66 in SOT-143

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.

R66 on a chip resistor

0.66 Ω

0.66 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 0.66 Ω. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 0.66 Ω on the board is a fault. Open, or well above 0.66 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 0.66 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 (USP-6C, SOT-23-5, SOT-23), R66 is a part code instead. Those parts are listed below.

1 part in SOT-143 is printed R66

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.

  • 2SC4091QSOT-1434 pins, RenesasNot recorded4 pinsRenesas
    What it is
    Not recorded
    Maker
    Renesas
    Package
    SOT-143
    Pins
    4
    Details
    npn RF fT 4GHz hfe 50-100
    Source
    Published code list

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

  • 1 more part has no package on record. Nothing rules it out, so it stays.
    • 2SC4091-QRF transistor, NEC ElectronicsRF transistorNot recordedNEC Electronics
      What it is
      RF transistor
      Maker
      NEC Electronics
      Package
      Not recorded
      Pins
      Not recorded
      Details
      NPN transistor: UHF, 15V, 5mA, 50mW, B=50..100, 4GHz
      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.

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.

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.

Printed with a code easy to misread as R66

One character differs, and it is one that is easy to confuse under a lamp. 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.