SMD code 55R
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.
55R on a chip resistor
55 Ω
55 Ω resistor
A trailing R marks the value in ohms, with nothing after the decimal point. The same marking also reads as 3.65 Ω, and nothing in the code says which; the body of the part does.
Other readings of the same characters, most likely first
- 3.65 Ω resistor, 1%
Check it with a meter
Lift one end and measure across it. A good one reads 55 Ω. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 55 Ω on the board is a fault. Open, or well above 55 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 55 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 (SOT-23-5, SOT-23, SMA), 55R is a part code instead. Those parts are listed below.
5 parts are printed 55R
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.
APL5155SOT-23-5LDO regulator, 5 pins, AnpecLDO regulatorSOT-23-55 pinsAnpec
- What it is
- LDO regulator
- Maker
- Anpec
- Package
- SOT-23-5
- Pins
- 5
- Details
- 3.3V version; High Input Voltage, Low Quiescent Current, 150mA LDO Regulator
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Voltage regulator.
APL5155ESOT-23-5LDO regulator, 5 pins, AnpecLDO regulatorSOT-23-55 pinsAnpec
- What it is
- LDO regulator
- Maker
- Anpec
- Package
- SOT-23-5
- Pins
- 5
- Details
- 3.3V version; High Input Voltage, Low Quiescent Current, 150mA LDO Regulator
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Voltage regulator.
S505TRSOT-143RF amplifier (MMIC), 4 pins, VishayRF amplifier (MMIC)SOT-1434 pinsVishay
- What it is
- RF amplifier (MMIC)
- Maker
- Vishay
- Package
- SOT-143
- Pins
- 4
- Details
- dg mosfet MOSIC 5V uhf tv tuners
- Source
- Published code list
Is it dead? The meter test is below: RF amplifier.
UM14239SSOT-23LDO regulator, 3 pins, Union SemiconductorLDO regulatorSOT-233 pinsUnion Semiconductor
- What it is
- LDO regulator
- Maker
- Union Semiconductor
- Package
- SOT-23
- Pins
- 3
- Details
- Linear voltage regulator IC: LDO, 3.9V±2%, 300mA
- Source
- Published code list
Is it dead? The meter test is below: Voltage regulator.
1 more part has no package on record
TK11355CMTokNot recordedNot recordedNot recordedTok
- What it is
- Not recorded
- Maker
- Tok
- Package
- Not recorded
- Pins
- Not recorded
- Details
- VR-IC: LDO, -CE, 5,5V±5%, 170mA
- Source
- Published code list
Is it dead? The meter test is below: Voltage regulator.
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.
Voltage regulator
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.
RF amplifier
Voltage, board powered, on the output pin that the bias resistor or choke feeds.
Working, it reads
The output pin sits at the device voltage the datasheet gives, a few volts, below the supply.
Dead, it reads
- Output pin at 0 V, or near 0 Ω to ground with the power off: shorted inside.
- Output pin at the full supply voltage: open inside, no current flowing.
- On the board:
- Measured on the board with power on; the bias network is part of the reading.
- 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 figures depend on the part and its bias resistor. The datasheet gives both.
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 55R
One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.
Did you find your part?
Open this in the search to correct a character or try another package.