SMD marking

18K

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.

18K on a chip resistor

18 kΩ

18 kΩ resistor

The K is both the decimal point and the multiplier: 18 kΩ.

Check it with a meter

Lift one end and measure across it. A good one reads 18 kΩ. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 18 kΩ on the board is a fault. Open, or well above 18 kΩ, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 18 kΩ. A burnt resistor usually means the part it feeds drew too much, so find that before fitting a new one.

On a transistor or diode body (SMB, SOT-23), 18K is a part code instead. Those parts are listed below.

Not sure which one you have?

Answer up to 4 quick questions and these 3 parts are ranked, with a meter test that settles it. It works on a dead part too.

The only part printed 18K in our tables

ESDBL18VA1

What it is: ESD protection diode
Maker: JSCJ
Package: Not recorded
Pins: Not recorded
Details: ESD protection diode, VRWM 18 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.

Datasheet

Printed with a code easy to misread

These parts are printed with a character that is easy to misread as what you typed. The odd one out is marked on each.

TVS diode, all SMB, 2 pins, all Vishay.

SMB8J14CAprinted 1BKSMB
Printed 1BK on the part. Easy to misread as 18K. Check that character with a loupe before you order anything.
What it is
TVS diode
Maker
Vishay
Package
SMB
Pins
2
Details
1000 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 SMB8J14CA, opens in a new tab
SMB10J14Aprinted 1BKSMB
Printed 1BK on the part. Easy to misread as 18K. Check that character with a loupe before you order anything.
What it is
TVS diode
Maker
Vishay
Package
SMB
Pins
2
Details
1000 W TVS diode, unidirectional
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 SMB10J14A, opens in a new tab

1 more part has a code that begins with 18K

Codes that begin with 18K

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

ATL432LIBQDBZprinted 1BKPSOT-23Voltage reference, 3 pins, Texas InstrumentsVoltage referenceSOT-233 pinsTexas Instruments
Printed 1BKP. Only the start matches what you typed, so this fits only if the rest of the marking is worn off.
What it is
Voltage reference
Maker
Texas Instruments
Package
SOT-23
Pins
3
Details
High Bandwidth Low-Iq Programmable Shunt Regulator
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 ATL432LIBQDBZ, opens in a new tab

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