0x400 — SMC: silent sensor
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.
On iPhone 13 mini
Gyroscope on the lower board (logic board sandwich separation)
High confidenceVerified sourceSMC: silent sensor
First check
No external part to order: check the logic board interposer (separation of the two layers) and the gyroscope pads; repair by reballing the sandwich.