SMD code T55 in SOT-23
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.
4 parts in SOT-23 are printed T55
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.
all SOT-23, 3 pins. What differs:
CHT55GPSOT-23PNP transistor, ChenmkoPNP transistorChenmko
- What it is
- PNP transistor
- Maker
- Chenmko
- Package
- SOT-23
- Pins
- 3
- Details
- PNP General Purpose Transistor, 60 V, 0.5 A
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: PNP transistor.
NVRGS055N06CLSOT-23N-channel MOSFET, onsemiN-channel MOSFETonsemi
- What it is
- N-channel MOSFET
- Maker
- onsemi
- Package
- SOT-23
- Pins
- 3
- Details
- MOSFET - Power, Single N-Channel, Small Signal
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: N-channel MOSFET.
BZX84-A3V9SOT-23Zener diode, NXPZener diodeNXP
- What it is
- Zener diode
- Maker
- NXP
- Package
- SOT-23
- Pins
- 3
- Details
- 3.9 V ±1% voltage regulator (Zener) diode
- Source
- Published code list
Is it dead? The meter test is below: Zener diode.
CHT55PTSOT-23PNP transistor, Chenmko EnterprisePNP transistorChenmko Enterprise
- What it is
- PNP transistor
- Maker
- Chenmko Enterprise
- Package
- SOT-23
- Pins
- 3
- Details
- PNP transistor: AF, Sw, 60V, 500mA, B>100, 50MHz
- Source
- Published code list
Is it dead? The meter test is below: PNP transistor.
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.
PNP transistor
Diode range, part lifted or its base leg off the pad.
Working, it reads
Black 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.
N-channel MOSFET
Diode range, part lifted. Test drain to source first, then short gate to source and test again.
Working, it reads
Red probe on the source, black on the drain: about 0.4 to 0.9 V, the body diode. Open the other way. The gate reads open to both other pins, both ways.
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. Often all three pins end up shorted together.
- No body diode at all: failed open.
- On the board
- the gate usually has a resistor to the source, so gate to source reads that resistor, which is not a fault. A drain short can be the load. 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.
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.
Printed with a code easy to misread as T55
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 T55
For a marking with its end worn or burnt off. Each code has a page of its own.
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