The flight controller's own 5 V supply is too low or too high

What ArduPilot says:

• PreArm: Board (N.Nv) out of range N.N-N.Nv

The flight controller measures the 5 V rail it runs on. The message gives the reading and the allowed range: from BRD_VBUS_MIN (4.3 V by default) to 5.8 V, which is fixed. Below the range the processor and the sensors can reset in flight; above it they can be damaged.

What to do, most likely first

1. It is powered from USB only, and the port or the cable does not hold 5 V.

   CheckThe reading in the message is a little under the lower limit (4.0 to 4.3 V) and the battery is not connected.

   FixConnect the flight battery (props off): this is how it is powered in flight, and the reading that matters. For bench work use a short cable straight into the computer, not a hub.

2. Too much hangs on the board's 5 V regulator: video transmitter, LEDs, servos, a companion computer.

   CheckWith the battery connected the reading is still low, and it rises when you unplug those devices one by one.

   FixPower the heavy consumers from their own regulator (BEC). Servos never belong on the flight controller's 5 V.

3. The regulator or power module that feeds the board is set to the wrong voltage, or is failing.

   CheckMeasure the 5 V pads with a multimeter, battery connected. A reading above 5.8 V in the message points to a regulator meant for servos (6 V or more).

   FixReplace or set the regulator so the board gets 5.0 to 5.3 V. Do not fly on a supply that reads above 5.8 V.

Parameters to look at

Where to do it:Board & Wiring Planner