SMD marking
B4in SOT-363
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.
2 parts are printed B4
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.
PUMB4SOT-363Digital transistor (PNP, resistors built in), 6 pins, NexperiaDigital transistor (PNP, resistors built in)6 pinsNexperia
- What it is
- Digital transistor (PNP, resistors built in)
- Maker
- Nexperia
- Package
- SOT-363
- Pins
- 6
- Details
- 50 V, 100 mA PNP/PNP resistor-equipped transistor; R1 = 10 kΩ, R2 = open
- Source
- From the manufacturer's datasheet
Is it dead?
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:
- 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.
1 more part has no package on record. Nothing rules them out, so they stay.
SN74AUP1G02DPWLogic gate, 5 pins, Texas InstrumentsLogic gate5 pinsTexas Instruments
- What it is
- Logic gate
- Maker
- Texas Instruments
- Package
- Not recorded
- Pins
- 5
- Details
- Low-Power Single 2-Input Positive-NOR Gate
- Source
- From the manufacturer's datasheet
Is it dead?
Voltage with the board powered; ohms from each pin to ground with it off.
Working, it reads
Supply pin at its voltage and the output doing what the datasheet says. Readings between pins depend on the part.
Dead, it reads
- A pin near 0 Ω to ground or to the supply pin where an identical part does not read that: failed short.
- Supply present, output stuck: failed, or its load has.
- On the board:
- A pin shorted to ground on the board can be anything on that net. Lift the pin to be sure.
- Compare:
- The surest reference is the same IC on a working board, measured pin by pin.
- Watch for:
- Its protection diodes can read like junctions between pins, even like a transistor. That proves nothing either way.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
1 more part is printed with a code easy to misread as B4
Printed with a code easy to misread
One character differs, and it is one that is easy to confuse under a lamp. The odd one out is marked on each.
BAT68-04printed 84Schottky diode, InfineonSchottky diodeInfineon
Printed 84 on the part. Easy to misread as B4. Check that character with a loupe before you order anything.
- What it is
- Schottky diode
- Maker
- Infineon
- Package
- Not recorded
- Pins
- Not recorded
- Source
- From the manufacturer's datasheet
Is it dead?
Diode range, part lifted or one leg off the pad. Red probe on the anode.
Working, it reads
About 0.15 to 0.45 V anode to cathode, roughly half a silicon diode, and open the other way.
Dead, it reads
- The same reading both ways round, near 0 V with a continuous beep or the same middling value: shorted.
- A reading the wrong way round as well: leaky.
- Open both ways: failed open.
- On the board:
- 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 large Schottky can read about 0.1 V forward and beep like a short, and leaks a little the wrong way when good, more when warm. It is shorted only if it reads the same both ways. Measure it cold, beside an identical cold one.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
1 more part has a code that begins with B4
Codes that begin with B4
For a marking with its end worn or burnt off. Each one shows its full printed code.
ESDBNG4V5B1printed B4V5ESD protection diode, JSCJESD protection diodeJSCJ
Printed B4V5. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
- What it is
- ESD protection diode
- Maker
- JSCJ
- Package
- Not recorded
- Pins
- Not recorded
- Details
- ESD protection diode, VRWM 4.5 V
- Source
- From the manufacturer's datasheet
Is it dead?
Diode range, from the protected line to ground, part lifted if you can.
Working, it reads
A one-way part reads about 0.6 to 0.8 V forward and open in reverse. A two-way part reads open both ways. Arrays with several lines read as the datasheet's diagram draws them.
Dead, it reads
- From the line to ground, the same reading both ways, near 0 V with a continuous beep: shorted.
- A reading both ways on a one-way part: leaky.
- A one-way part open both ways: failed open.
- On the board:
- On the board, a line reading shorted to ground can be this part or anything else on that line. Lift it: if the short goes with it, it has failed.
- Compare:
- The same part on the next line or connector pin is the healthy reading to compare with.
- Watch for:
- A two-way part reads open both ways when it is good, exactly like one that has failed open. The meter cannot tell them apart; an identical part on the next line can.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Open this in the search to correct a character or try another package.