No power / no boot

Symptom	Check
Dead	5–15 V, ≥2 A; USB-C PD cable; hold power ~8 s until the LED is green
USB enumerates as DFU, no Linux	BOOT SEL still USB ROM — set normal, power-cycle
r24: no boot	SD seated, correct image, card not fake/corrupt — reflash
r30: no boot	eMMC image + normal straps; if OTP boot fuses wrong, depot
Reboot loop	journalctl -b; commd crashing should still leave Dropbear if the rootfs is intact

Linux never starts if the SoC stays in ROM. Photograph the switches before changing them.