How to recover a bricked nRF52840DK.

Question

We were developing an nRF52840 device and were working on MCUBOOT DFU firmware updates, and accidentally did an update rather than an upgrade, and now my nRF52840DK is bricked. I have two more on order as backup, but I figure it is a good learning experience to learn how to recover. 
 I have done all the things listed in this article. 
 https://devzone.nordicsemi.com/f/nordic-q-a/24592/my-nrf52-nrf51-dk-kit-doesn-t-work 
 Using my Windows 11 laptop, I can see the BOOTLOADER in Device Manager. I can reinstall the j-link-ob-sam3u128-v2-nordicsemi-170724.bin file. I have updated J-Link drivers. I can connect my Windows laptop to a separate nRF52832DK and everything works, so the development environment seems correct. I've tried these things with the IF BOOT/RESET switch held at power up, and not. I've tried these things on my MacBook, too. 
 When I tried to do a "nrjprog --recover --log", I get the log copied in below with a lot of "-1" responses. 
 I found a post about using a J-Link Commander to recover a device, but this post is more than 8 years old and doesn't cover the nRF52840DK. 
 https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/recover-the-nrf51-when-nrjprog-and-nrfgo-studio-co 
 Any thoughts on how to resurrect my trusty DK? 
 Best, 
 Steve

user2115 · Accepted Answer

Hi, 
 
 If your device is asserting early in the boot process, ie. it is basically performing a soft-reset in a loop, it can be hard to recover the nRF. 
 
 You can try to use j-link commander: 
 
 device nrf52840_xxaa
si 1
speed 1000
connect
 
 And see if it is able to successfully connect, and you can issue "erase" command to the nRF. 
 If that still fails, what you can do is to try to run this loop: 
 https://devzone.nordicsemi.com/f/nordic-q-a/45078/nrf52832-not-connected-anymore-after-first-trying-to-debug-keil/177579#177579 
 
 While continuously powering the nRF on/off. Note that if you're using the DK as a debugger, it is easiest to toggle power to the nRF by using the "nRF current measurement" pin header, via a jumper. 
 
 Kind regards, 
 Håkon

user38780 · Answer

Hi H&aring;kon, 
 This worked! Didn't have to use the loop, it worked with the simple J-Link Commander commands you listed. 
 Thank you so much! 
 Best, 
 Steve

How to recover a bricked nRF52840DK.

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