SMD marking

4Ain SOD-123F

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 4A in this package in our tables

BZT52C2V0

What it is: Zener diode
Maker: Diotec
Package: SOD-123F
Pins: 2
Details: SMD Planar Zener Diodes
Source: From the manufacturer's datasheet

Is it dead?

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:: 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.

Datasheet

8 more parts have codes that begin with 4A

Codes that begin with 4A

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

4SMF10CAprinted 4AXSOD-123FTVS diode, 2 pins, VishayTVS diode2 pinsVishay
Printed 4AX. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
TVS diode
Maker
Vishay
Package
SOD-123F
Pins
2
Details
400 W TVS diode, bidirectional
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.
Datasheetfor 4SMF10CA, opens in a new tab
4SMF11CAprinted 4AZSOD-123FTVS diode, 2 pins, VishayTVS diode2 pinsVishay
Printed 4AZ. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
TVS diode
Maker
Vishay
Package
SOD-123F
Pins
2
Details
400 W TVS diode, bidirectional
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.
Datasheetfor 4SMF11CA, opens in a new tab
6 more parts have no package on record. Nothing rules them out, so they stay.
- LMR51420XDDCprinted 4AXPDC-DC converter, 6 pins, Texas InstrumentsDC-DC converter6 pinsTexas Instruments
  Printed 4AXP. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  DC-DC converter
  Maker
  Texas Instruments
  Package
  Not recorded
  Pins
  6
  Details
  SIMPLE SWITCHER® Power Converter 4.5-V to 36-V, 2-A, Synchronous Buck Converter in a SOT-23 Package
  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.
  Datasheetfor LMR51420XDDC, opens in a new tab
- LMR51420XFDDCprinted 4AXFDC-DC converter, 6 pins, Texas InstrumentsDC-DC converter6 pinsTexas Instruments
  Printed 4AXF. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  DC-DC converter
  Maker
  Texas Instruments
  Package
  Not recorded
  Pins
  6
  Details
  SIMPLE SWITCHER® Power Converter 4.5-V to 36-V, 2-A, Synchronous Buck Converter in a SOT-23 Package
  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.
  Datasheetfor LMR51420XFDDC, opens in a new tab
- LMR51420YDDCprinted 4AYPDC-DC converter, 6 pins, Texas InstrumentsDC-DC converter6 pinsTexas Instruments
  Printed 4AYP. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  DC-DC converter
  Maker
  Texas Instruments
  Package
  Not recorded
  Pins
  6
  Details
  SIMPLE SWITCHER® Power Converter 4.5-V to 36-V, 2-A, Synchronous Buck Converter in a SOT-23 Package
  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.
  Datasheetfor LMR51420YDDC, opens in a new tab
- LMR51420YFDDCprinted 4AYFDC-DC converter, 6 pins, Texas InstrumentsDC-DC converter6 pinsTexas Instruments
  Printed 4AYF. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  DC-DC converter
  Maker
  Texas Instruments
  Package
  Not recorded
  Pins
  6
  Details
  SIMPLE SWITCHER® Power Converter 4.5-V to 36-V, 2-A, Synchronous Buck Converter in a SOT-23 Package
  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.
  Datasheetfor LMR51420YFDDC, opens in a new tab
- PLZ4V3Aprinted 4A3Zener diode, VishayZener diodeNot recordedVishay
  Printed 4A3. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  Zener diode
  Maker
  Vishay
  Package
  Not recorded
  Pins
  Not recorded
  Details
  4.3 V Zener diode
  Source
  From the manufacturer's datasheet
  Is it dead?
  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:
  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.
  Datasheetfor PLZ4V3A, opens in a new tab
- PLZ4V7Aprinted 4A7Zener diode, VishayZener diodeNot recordedVishay
  Printed 4A7. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
  What it is
  Zener diode
  Maker
  Vishay
  Package
  Not recorded
  Pins
  Not recorded
  Details
  4.7 V Zener diode
  Source
  From the manufacturer's datasheet
  Is it dead?
  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:
  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.
  Datasheetfor PLZ4V7A, opens in a new tab

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