SMD code R3954
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.
R3954 on a chip inductor
0.4 µH
0.4 µH inductor
The R stands in for the decimal point, in microhenries: 0.4 µH. SMD power inductors below 10 µH are printed this way. The same marking also reads as 0.4 pF on a capacitor, and nothing in the code says which; the body of the part does.
Other readings of the same characters, most likely first
- 0.4 pF capacitor
Check it with a meter
Measure it on an LCR meter, out of circuit. A good one reads close to 0.4 µH. An ohmmeter only shows the winding resistance, which is a fraction of an ohm on a good part and says nothing about the value; open circuit means the winding has failed. Shorted turns still read near 0 Ω on an ohmmeter, so only the LCR meter, or an identical part beside it, shows them. A failed reading does not change what to fit: the marking still says 0.4 µH.
On a transistor or diode body (SOT-23-6), R3954 is a part code instead. Those parts are listed below.
The only part printed R3954 in our tables
GSFR3954
- What it is
- Complementary MOSFET pair (N-channel and P-channel)
- Maker
- Good-Ark
- Package
- SOT-23-6
- Pins
- 6
- Details
- N + P channel MOSFET pair
- Source
- Manufacturer datasheet
Is it dead?
Diode range, part lifted. Test drain to source first, then short gate to source and test again. Test each MOSFET on its own pins, as the datasheet's pinout gives them.
Working, it reads
One way between drain and source reads about 0.4 to 0.9 V, the body diode, and the other way open. The gate reads open to both other pins.
Dead, it reads
- Drain to source the same both ways, near 0 V with a continuous beep, and still so after shorting gate to source: shorted. The classic failure.
- The gate reads low to source or drain: gate shorted.
- No body diode at all: failed open.
- On the board
- the gate usually has a resistor to the source, which reads as that resistor and is not a fault. Lift a leg to be sure.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- The diode range can charge the gate enough to turn the part on, and then drain to source reads near 0 both ways on a good part. Short gate to source and test again before you condemn it.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
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