SMD code A4s
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.
The last letter, s, is lower case, which on NXP and Philips parts is a date or factory code, so it was set aside and A4 was searched.
243 parts are printed A4s
Not sure which one you have?
Answer up to 4 quick questions and these 50 parts are ranked, with a meter test that settles it. It works on a dead part too.
FM4004-N-Q1SOD-323Rectifier, 2 pins, Formosa MicrosemiRectifierSOD-3232 pinsFormosa Microsemi
- What it is
- Rectifier
- Maker
- Formosa Microsemi
- Package
- SOD-323
- Pins
- 2
- Details
- Rectifier diode
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
FM4004-Q1SMARectifier, 2 pins, Formosa MicrosemiRectifierSMA2 pinsFormosa Microsemi
- What it is
- Rectifier
- Maker
- Formosa Microsemi
- Package
- SMA
- Pins
- 2
- Details
- Rectifier diode
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
FMA4ASOT-23-5Digital transistor (resistors built in), 5 pins, ROHMDigital transistor (resistors built in)SOT-23-55 pinsROHM
- What it is
- Digital transistor (resistors built in)
- Maker
- ROHM
- Package
- SOT-23-5
- Pins
- 5
- Details
- Emitter common(dual digital transistor)
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Digital transistor.
FMOS6107SOT-23MOSFET, 3 pins, Formosa MicrosemiMOSFETSOT-233 pinsFormosa Microsemi
- What it is
- MOSFET
- Maker
- Formosa Microsemi
- Package
- SOT-23
- Pins
- 3
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: MOSFET.
GSA4SOD-123FRectifier, 2 pins, Good-ArkRectifierSOD-123F2 pinsGood-Ark
- What it is
- Rectifier
- Maker
- Good-Ark
- Package
- SOD-123F
- Pins
- 2
- Details
- Rectifier, 400 V, 1 A
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
LBAV70DW1T1GSOT-363Switching diode, 6 pins, LRCSwitching diodeSOT-3636 pinsLRC
- What it is
- Switching diode
- Maker
- LRC
- Package
- SOT-363
- Pins
- 6
- Details
- Switching diode, VR 100 V, IF 250 mA, VF Max 1.25 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
LBAV70LT1GSOT-23Switching diode, 3 pins, LRCSwitching diodeSOT-233 pinsLRC
- What it is
- Switching diode
- Maker
- LRC
- Package
- SOT-23
- Pins
- 3
- Details
- Switching diode, VR 100 V, IF 200 mA, VF Max 1.25 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
LBAV70WT1GSOT-323Switching diode, 3 pins, LRCSwitching diodeSOT-3233 pinsLRC
- What it is
- Switching diode
- Maker
- LRC
- Package
- SOT-323
- Pins
- 3
- Details
- Switching diode, VR 70 V, IF 200 mA, VF Max 1 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
LD39020ADTPU11RDFNLDO regulator, STMicroelectronicsLDO regulatorDFNNot recordedSTMicroelectronics
- What it is
- LDO regulator
- Maker
- STMicroelectronics
- Package
- DFN
- Pins
- Not recorded
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Voltage regulator.
6 more parts have no package on record
FM4004-SFRectifier, Formosa MicrosemiRectifierNot recordedNot recordedFormosa Microsemi
- What it is
- Rectifier
- Maker
- Formosa Microsemi
- Package
- Not recorded
- Pins
- Not recorded
- Details
- Rectifier diode
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
FM4004-SF-Q1Rectifier, Formosa MicrosemiRectifierNot recordedNot recordedFormosa Microsemi
- What it is
- Rectifier
- Maker
- Formosa Microsemi
- Package
- Not recorded
- Pins
- Not recorded
- Details
- Rectifier diode
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
HFCN-4400+RF filter, Mini-CircuitsRF filterNot recordedNot recordedMini-Circuits
- What it is
- RF filter
- Maker
- Mini-Circuits
- Package
- Not recorded
- Pins
- Not recorded
- Details
- LTCC filter, 5000-10100 MHz
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: This part.
HFCN-4400D+RF filter, Mini-CircuitsRF filterNot recordedNot recordedMini-Circuits
- What it is
- RF filter
- Maker
- Mini-Circuits
- Package
- Not recorded
- Pins
- Not recorded
- Details
- LTCC filter, 5000-10100 MHz
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: This part.
KDZ36EVZener diode, KECZener diodeNot recordedNot recordedKEC
- What it is
- Zener diode
- Maker
- KEC
- Package
- Not recorded
- Pins
- Not recorded
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
LBAV70TT1GSwitching diode, LRCSwitching diodeNot recordedNot recordedLRC
- What it is
- Switching diode
- Maker
- LRC
- Package
- Not recorded
- Pins
- Not recorded
- Details
- Switching diode, VR 70 V, IF 200 mA, VF Max 1.25 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Silicon diode.
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.
Digital transistor
Ohms range, part lifted. The datasheet gives the built-in resistors: R1 in series with the base, R2 from base to emitter.
Working, it reads
Base to emitter reads about R1 plus R2 either way round, about 20 kΩ on a 10 k and 10 k part, give or take their wide tolerance. Collector to emitter reads open. A part with no R2 reads a junction behind R1 one way instead.
Dead, it reads
- Collector to emitter the same both ways, near 0 Ω with a continuous beep: shorted.
- From the base, open or far above R1 plus R2: R1 has failed. Static damage shows here most often.
- Base to emitter near 0 Ω: failed short.
- 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:
- The readings depend on the resistor values, so an identical part elsewhere on the board is the surest reference. Measure it the same way.
- Watch for:
- On the diode range a good part with 10 kΩ resistors reads open on every pair, so a good part looks dead there. Use the ohms range.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
MOSFET
Diode range, part lifted. Test drain to source first, then short gate to source and test again.
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.
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.
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.
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.
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