SMD code 54P
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.
54P on a chip capacitor
54 pF
54 pF capacitor
The p is both the decimal point and the unit: 54 pF.
Check it with a meter
Lift one end and measure it on a capacitance range. A good one reads close to 54 pF. In circuit the meter also sees everything connected across it, so the reading means little until it is out. A failed one usually reads near 0 Ω, or a steady low resistance, on the ohms range, often from a crack. On the board a shorted capacitor shorts its whole rail. A failed reading does not change what to fit: the marking still says 54 pF.
On a transistor or diode body (SOT-23, SOIC-8, DFN), 54P is a part code instead. Those parts are listed below.
4 parts are printed 54P
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.
LC0504NDFNESD protection diode, LeiditechESD protection diodeDFNNot recordedLeiditech
- What it is
- ESD protection diode
- Maker
- Leiditech
- Package
- DFN
- Pins
- Not recorded
- Details
- ESD protection diode, VRWM 5 V, Cj 0.8 pF
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: TVS or ESD protection diode.
BSR17ASOT-23NPN transistor, 3 pins, Philips SemiconductorsNPN transistorSOT-233 pinsPhilips Semiconductors
- What it is
- NPN transistor
- Maker
- Philips Semiconductors
- Package
- SOT-23
- Pins
- 3
- Details
- Bipolar transistor, 40 V, 0.2 A
- Source
- Published code list
Is it dead? The meter test is below: NPN transistor.
ELM85241BSOT-23LDO regulator, 3 pins, ELM TechnologyLDO regulatorSOT-233 pinsELM Technology
- What it is
- LDO regulator
- Maker
- ELM Technology
- Package
- SOT-23
- Pins
- 3
- Details
- Linear voltage regulator IC: LDO, 2.4V±2%, 600mA
- Source
- Published code list
Is it dead? The meter test is below: Voltage regulator.
UM36547SSOT-23LDO regulator, 3 pins, Union SemiconductorLDO regulatorSOT-233 pinsUnion Semiconductor
- What it is
- LDO regulator
- Maker
- Union Semiconductor
- Package
- SOT-23
- Pins
- 3
- Details
- Linear voltage regulator IC: LDO, 4.7V±2%, 300mA
- 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.
TVS or ESD protection diode
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
- , 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.
NPN transistor
Diode range, part lifted or its base leg off the pad.
Working, it reads
Red probe on the base 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.
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.
Codes that begin with 54P
For a marking with its end worn or burnt off. Each code has a page of its own.
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