How to write the bootloader back to nRF52840 Dongle ?

Question

hi,

I have accidentally selected "Erase All" under the Segger Embedded Studio, now my nRF52840 Dongle unable to show its USB port under Windows 10 Device Manager anymore.

How to resolve this issues and where to get the right bootloader image for nRF52840, as the nRF52840 Dongle unable to report its serial port, Segger J-Link was unable to connect.

Please advise.

rickygai · Accepted Answer

Dear friends, This time, I soldered a 1.27mm IDC Male Socket to the back of nRF52840 Dongle very carefully, I wish it has a rectangle box marked on that area to position the SWD interface while soldering :o) 
 I am using Segger J-LINK EDU to burn bootloader to this dongle, you have to connect the USB power supply as well otherwise you will be seeing error messages below: ERROR: Low voltage detected at the target. Please make sure the device is ERROR: properly supplied. Error while burning bootloader. 
 
 This time the J-LINK clone won't work on such configuration, and it caused DLL error under Arduino IDE 1.8.16 as shown below: Error while burning bootloader. ERROR: JLinkARM DLL reported an error. Try again. If error condition ERROR: persists, run the same command again with argument --log, contact Nordic ERROR: Semiconductor and provide the generated log.log file to them. 
 Well, I won't bother that much to investigate further, just use the genuine Segger J-LINK EDU for my works to be safe. You have to be careful in using clone J-LINK because its VTref or pin 1 of the JTAG interface is 3.3V OUTPUT. The VTref of Segger J-LINK EDU is INPUT VOLTAGE reference based on the datasheet. After the bootloader is written, you may disconnect the J-LINK device, connect the dongle with USB, now the new bootloader will establish a serial COM port under Windows, use that serial port to upload sketch easily under Arduino IDE or PlatformIO IDE. The successfully sketch uploaded messages are like below: Sketch uses 40004 bytes (4%) of program storage space. Maximum is 815104 bytes. Global variables use 6876 bytes (2%) of dynamic memory, leaving 230692 bytes for local variables. Maximum is 237568 bytes. Upgrading target on COM16 with DFU package C:\Users\RICKYG~1\AppData\Local\Temp\arduino_build_772033	est.ino.zip. Flow control is disabled, Single bank, Touch disabled ######################################## ####################################### Activating new firmware Device programmed. Depends on which nRF52840 .HEX bootloader file you use, I am using feather_nrf52840_express_bootloader-0.6.2_s140_6.1.1.hex on Nordic nRF52840 Dongle just to test it under Arduino platform. Hopes, this help.