BMM350 reports very high compensated magnetic field magnitude (~300–350 µT) on one PCB but normal Earth field on another identical PCB

Hello,

I am working with the Bosch BMM350 magnetometer and observing unusually high magnetic field readings on one PCB, while another PCB with the same schematic and firmware behaves normally.

Observed behavior

• Output values are assumed to be in µT

• Raw compensated readings (example):

  mx ≈ +246 µT

  my ≈ +236 µT

  mz ≈ −27 µT

• Magnitude:

  ∣B∣=mx2+my2+mz2≈340μT

• On a second PCB:

  • |B| ≈ 40–60 µT, as expected for Earth’s magnetic field

• What has been checked

  • Same firmware, same API usage, same environment

  • Communication verified, no obvious I2C issues

  • Temperature compensation working

  • Nearby power inductor was removed, but readings did not change

  • No strong dynamic current-related variation observed

  • Calibration attempts fail or are unstable (ellipsoid fit issues on both pcbs)

• Questions

  1. Can bmm350_hal_read_compensated()output be confirmed as µT?

  2. Can the BMM350 retain a persistent magnetic offset after exposure to a strong field, even if the source is removed?

  3. Is calling BMM350_magnetic_reset_and_wait()recommended after assembly or suspected magnetic shock?

  4. Besides inductors, are ferrite beads, shield cans, connectors, or PCB assembly effects known to cause offsets of ~300 µT?

  5. Is such a large static offset realistically recoverable via calibration, or should the PCB be considered magnetically unsuitable?

  Any guidance would be appreciated.