H520 / H Plus Won’t Arm? Pre-Flight Checklist

When an H520 or H Plus refuses to arm, work through this list before you start replacing parts.

1. GPS lock: the drone needs a solid GPS lock to arm in most modes. See GPS stuck on Acquiring.
2. Compass: calibrate in an open area away from metal.
3. Battery: use a healthy, fully charged battery. A weak battery can prevent arming.
4. No-fly zone: if you are in a no-fly zone, the drone will not arm until it is unlocked. NFZ unlock service.
5. ST16S controller: check that the controller is bound and calibrated.
6. Error messages: read exactly what the controller says. "Compass error," "GPS not ready," and "NFZ restricted" each point to a different fix.

If everything checks out and it still will not arm, the flight controller or a motor/ESC fault is likely. That is bench diagnosis: mail-in H520 diagnostic.