SMD marking

T43in SOT-23-5

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.

The only part printed T43 in this package in our tables

TPS73618DBV

What it is: LDO regulator
Maker: Texas Instruments
Package: SOT-23-5
Pins: 5
Details: Capacitor-Free, NMOS, 400mA, Low-Dropout Regulator With Reverse Current Protection
Source: From the manufacturer's datasheet

Is it dead?

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.

Datasheet

3 more parts have codes that begin with T43

Codes that begin with T43

For a marking with its end worn or burnt off. Each one shows its full printed code.

MOSFET, all Alpha & Omega Semiconductor.

AONS74304printed 74304
Printed 74304. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
MOSFET
Maker
Alpha & Omega Semiconductor
Package
Not recorded
Pins
Not recorded
Details
Low-voltage (12-30 V) MOSFET
Source
From the manufacturer's datasheet
Is it dead?
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:
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.
Datasheetfor AONS74304, opens in a new tab
AONS74306printed 74306
Printed 74306. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
MOSFET
Maker
Alpha & Omega Semiconductor
Package
Not recorded
Pins
Not recorded
Details
Low-voltage (12-30 V) MOSFET
Source
From the manufacturer's datasheet
Is it dead?
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:
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.
Datasheetfor AONS74306, opens in a new tab
AONS74312printed 74312
Printed 74312. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
MOSFET
Maker
Alpha & Omega Semiconductor
Package
Not recorded
Pins
Not recorded
Details
Low-voltage (12-30 V) MOSFET
Source
From the manufacturer's datasheet
Is it dead?
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:
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.
Datasheetfor AONS74312, opens in a new tab

Open this in the search to correct a character or try another package.