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SMD code 321 in USP-6C

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.

1 part in USP-6C is printed 321

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.

  • XC6505A621ERUSP-6CLDO regulator, 6 pins, TorexLDO regulator6 pinsTorex
    What it is
    LDO regulator
    Maker
    Torex
    Package
    USP-6C
    Pins
    6
    Details
    Linear voltage regulator IC: LDO, 6.2V±1%, 200mA, +CE
    Source
    Published code list

    Is it dead? The meter test is below: Voltage regulator.

  • 2 more parts have no package on record. Nothing rules them out, so they stay.
    • TCK321GLoad switch, ToshibaLoad switchNot recordedToshiba
      What it is
      Load switch
      Maker
      Toshiba
      Package
      Not recorded
      Pins
      Not recorded
      Details
      36 V, Dual Inputs - Single Output Power Multiplexer IC with Over Voltage Protection
      Source
      Manufacturer datasheet

      Is it dead? The meter test is below: Load switch.

      Datasheetfor TCK321G, opens in a new tab
    • ADA4432-1BCPZ-R28 pins, Analog DevicesNot recorded8 pinsAnalog Devices
      What it is
      Not recorded
      Maker
      Analog Devices
      Package
      Not recorded
      Pins
      8
      Source
      Published code list

      Is it dead? The meter test is below: This part.

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.

Load switch

Voltage, board powered, black probe on ground.

Working, it reads

Switched on, the output pin sits at the input voltage. Switched off, it sits near 0 V.

Dead, it reads

  • Output at the input voltage while switched off: the pass element has shorted.
  • Input present and switched on, no output: failed open, or shut down into a shorted load. Power off and measure output to ground.
On the board:
An output near 0 Ω to ground is usually the load. Lift the output pin to see which.
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 pinout and whether the enable is active high or low differ between parts. 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.

This part

Diode range and ohms range, part lifted.

Working, it reads

Depends on what it is. The datasheet, or an identical part, says.

Dead, it reads

  • Between two pins, the same reading both ways, near 0 V with a continuous beep: shorted.
  • Open between every pair of pins: failed open, or a part that reads open when working.
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.

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 321

One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.

Codes that begin with 321

For a marking with its end worn or burnt off. Each code has a page of its own.

Codes not listed here are printed on 2 more parts.

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