Debugger fails connecting to MCU

[A.P]

Hi!
I'm working on a custom board with the nRF52840 via an SWD connection, from a debug out on an nRF52840 DK.

The debugger fails to connect to one of my boards, even though the MCU is continuously updating its display, so I know it's alive. The debugger and connector are the same ones I use for other boards, without any issues so they work as well.

I'm attaching a log generated when I tried to erase the board using nrfjprog -e and -recover. Please let me know if you find anything I can use in the log.

Thanks!

log.log

[haakonsh]

What's the VDD voltage of the custom board?

The OB J-link only supports 2.8V. 

[A.P]

The VDD range is ~3V. But the same exact setup connects to different copies of the same board, so I don't think the setup is the problem here.

[haakonsh]

~3V is fine, but given that you have other working boards it indicates an HW issue. 

Have you set the APPROTECT in any/all your boards? 

I think a logic scope of the SWDIO and CLK lines might possibly show symptoms of some HW issues.

I would also monitor VDD with a high sample rate oscilloscope during a recovery procedure. 

Measuring current consumption can also reveal symptoms as currents above 15-20mA indicate an HW issue.