"Could not power-up debug power domain" from JLinkExe when using nRF52-DK to program custom nRF52-card

[ThomasL]

This is what we get from JLinkExe: Found SWD-DP with ID 0x2BA01477 Could not power-up debug power domain. Can not connect to target.

This all happens when we use P19 to connect to the external board. What does this mean, and how might we get around the issue? The connected board does have external power (3.3V).

[bjorn-spockeli]

Have you verified that the connections are correct? Please refer the nRF52 DK Hardware files, found here for the pinout of the P19 header. The external board must be powered with the same voltage levels as the DK, in order to be detected.