iPhone 13 mini — sensor array 0x400: Gyroscope on the lower board

What does this code mean?

SMC “BSC failure” panic: the system management controller (built into the SoC) periodically waits for a response from each mandatory sensor; on the iPhone 13 mini, the gyroscope on the lower board must respond; here it can no longer be reached. With no response, it forces a restart, which repeats roughly every 3 minutes (≈180 s) as long as the sensor stays silent.

Which part to test first?

No external part to order: check the logic board interposer (separation of the two layers) and the gyroscope pads; repair by reballing the sandwich.

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