We have a several of these boards coming back from customers with an intermittent problem (screen stays black, not running software). After investigating, the boards sometimes start up ok but mostly no bootloader kicks in. There is no output on debug serial port.
We run with F3S file system. I've noticed with these boards (even ok boards) sometimes they take ~7 seconds before debug output is produced from bootloader.
LED on the board is lit (orange) which is normal.
In this vegetative state nothing helps, no reset, no powercycle. Only after been powered off for a while they come back to normal when powered.
I read in the documentation about Boot Fail on HW rev 1.1 till 1.3.
We have rev 1.31.
What can we measure on the boards to confirm it is still Boot Fail?