Wiring diagram

My servo isn’t moving

Almost always power, ground, the signal pin, or the cardboard stalling the horn — not a broken servo.

The problem

You uploaded the sketch. The board LED is on. The servo sits still, jitters, or hums.

Servo: A small motor that turns to an angle and holds there. Overhaul QA uses micro servos (SG90 class) for arms, gates, claws, and drawbridges.
Stall: The servo is commanded to move but the cardboard or a screw is blocking it. It will hum, get warm, and still not turn.

1
Confirm three wires: signal to the pin in the code (often D9), red to 5V, brown/black to GND. A servo on signal-only will not move. This showed up more than once in QA on the arm and sorter.
2
Open the generated code and find attach(9) or the pin in the diagram. If you plugged the signal into D10 but the code says 9, move the wire or change the number so they match. They must match.
3
Lift the horn off the cardboard and upload again. If it now sweeps, the joint is too tight. Widen the hole or free the glue. Do not keep running a stalled servo; it heats up.
4
If it still does nothing, try 5V from the board with USB connected. A weak battery pack under-volts the servo. QA benches use USB power for the first bring-up.
5
Swap in a second servo if you have one. If the second servo works on the same wires, the first servo is the fault. If neither works, the wiring or pin number is still wrong.

If you walked the steps and the mechanism still does not move, write to us. This is the fallback, not the first stop.