SMD code 18A
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.
18A on a chip resistor
150 Ω
150 Ω resistor, 1%
EIA-96 precision code: 18 selects 1.5 from the E96 series and A multiplies by 100. These are 1% parts.
Check it with a meter
Lift one end and measure across it. A good one reads 150 Ω within 1%. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 150 Ω on the board is a fault. Open, or well above 150 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 150 Ω. 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 (SMA, SMC, SOT-23), 18A is a part code instead. Those parts are listed below.
5 parts are printed 18A
Not sure which one you have?
Answer up to 4 quick questions and these 5 parts are ranked, with a meter test that settles it. It works on a dead part too.
all Vishay. What differs:
1.5SMC18ASMCTVS diode, 2 pinsTVS diodeSMC2 pins
- What it is
- TVS diode
- Maker
- Vishay
- Package
- SMC
- Pins
- 2
- Source
- From the manufacturer's datasheet
Is it dead? The meter test is below: TVS or ESD protection diode.
SML4746ASMAZener diode, 2 pinsZener diodeSMA2 pins
- What it is
- Zener diode
- Maker
- Vishay
- Package
- SMA
- Pins
- 2
- Details
- 18 V Zener diode
- Source
- From the manufacturer's datasheet
Is it dead? The meter test is below: Zener diode.
VCAN18A2-03GSOT-323ESD protection diode, 3 pinsESD protection diodeSOT-3233 pins
- What it is
- ESD protection diode
- Maker
- Vishay
- Package
- SOT-323
- Pins
- 3
- Details
- Bidirectional Symmetrical (BiSy) Low Capacitance, Dual-Line ESD Protection Diode in SOT-323
- Source
- From the manufacturer's datasheet
Is it dead? The meter test is below: TVS or ESD protection diode.
VCAN18A2-03SSOT-23ESD protection diode, 3 pinsESD protection diodeSOT-233 pins
- What it is
- ESD protection diode
- Maker
- Vishay
- Package
- SOT-23
- Pins
- 3
- Details
- Bidirectional Symmetrical (BiSy) Low Capacitance, Dual-Line ESD Protection Diode in SOT-23
- Source
- From the manufacturer's datasheet
Is it dead? The meter test is below: TVS or ESD protection diode.
1 more part has no package on record
PLZ18AZener diodeZener diodeNot recordedNot recorded
- What it is
- Zener diode
- Maker
- Vishay
- Package
- Not recorded
- Pins
- Not recorded
- Details
- 18 V Zener diode
- Source
- From the manufacturer's datasheet
Is it dead? The meter test is below: Zener diode.
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.
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.
Open this in the search to correct a character or try another package.