SMD code M558
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.
M558 on a chip resistor
558 kΩ
558 kΩ resistor
The M is both the decimal point and the multiplier: 558 kΩ.
Check it with a meter
Lift one end and measure across it. A good one reads 558 kΩ. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 558 kΩ on the board is a fault. Open, or well above 558 kΩ, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 558 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 (SOT-23, SOT-23-5), M558 is a part code instead. Those parts are listed below.
The only part printed M558 in our tables
AMS5358
- What it is
- LDO regulator
- Maker
- AMOS Technology
- Package
- SOT-23
- Pins
- 3
- Details
- Linear voltage regulator IC: LDO, 5.8V±2%, 500mA
- Source
- Published code list
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.
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