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Recipe

Find a wiring fault

Use when: a circuit misbehaves, resets, runs hot or does nothing, and the firmware is known to work

Goal: the faulty connection found with nothing further damaged

Taught in Protection and wiring failures

Quick recipe

  1. Remove power first
  2. Check + to − with the meter, powered off
  3. Check polarity and the supply voltage, powered on
  4. Check every ground is joined
  5. Measure the signals
  1. 1

    On heat, a smell or a USB warning, unplug every source before anything else.

    Why: most faults get worse with every second of power, and none get better.

  2. 2

    Use continuity mode between the supply rail and ground.

    • it beeps — find the short before powering up again.
    • silent — move on.

    Why: a short is the fault most likely to damage something next time.

  3. 3

    Measure at the board's own pins, not at the supply's terminals.

    Why: a reversed or sagging supply, or a broken wire on the way, shows up only at the board.

  4. 4

    Continuity between each board's GND and every other GND in the project.

    Why: a missing or loose ground makes good signals read as nonsense.

  5. 5

    Compare each signal's voltage with the receiving pin's thresholds and maximum.

    Why: a signal in the grey zone, or above the maximum, explains wrong readings and dead pins.

Common mistakes

  • Probing a powered circuit in continuity mode.
  • Measuring the supply at the power supply instead of at the board.
  • Checking only one ground wire when there are several boards.