SMD code 3B1 in SMA
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.
2 parts in SMA are printed 3B1
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.
SMA3EZ16D5SMAZener diode, DOWOZener diodeDOWO
- What it is
- Zener diode
- Maker
- DOWO
- Package
- SMA
- Pins
- 2
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
SMA3Z16ASMAZener diode, RectronZener diodeRectron
- What it is
- Zener diode
- Maker
- Rectron
- Package
- SMA
- Pins
- 2
- Details
- Zener diode: 15.30..171.0V, Izt=15.0mA, Zzt=15.0, 3W
- Source
- Published code list
Is it dead? The meter test is below: Zener diode.
2 more parts have no package on record. Nothing rules them out, so they stay.
LM4318PComplementary MOSFET pair (N-channel and P-channel), LeiditechComplementary MOSFET pair (N-channel and P-channel)Leiditech
- What it is
- Complementary MOSFET pair (N-channel and P-channel)
- Maker
- Leiditech
- Package
- Not recorded
- Pins
- Not recorded
- Details
- N+P channel MOSFET pair
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: MOSFET pair.
XC6221B321GRLDO regulator, TorexLDO regulatorTorex
- What it is
- LDO regulator
- Maker
- Torex
- Package
- Not recorded
- Pins
- Not recorded
- Details
- Linear voltage regulator IC: LDO, 3.2V±1%, 200mA, +CE, CL
- Source
- Published code list
Is it dead? The meter test is below: Voltage regulator.
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.
Zener diode
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
- 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.
MOSFET pair
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.
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.
Printed with a code easy to misread as 3B1
One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.
Codes that begin with 3B1
For a marking with its end worn or burnt off. Each code has a page of its own.
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