cannot enter bootloader mode on nrf52840 dongle anymore

[Ivo H]

Dear all,

I could happily flash my firmware to my nrf52840 upon pressing reset button. When pressing the reset button the diode on the board started to beat red and via command:

nrfutil dfu usb-serial -pkg blinky.zip -p /dev/ttyACM0

I could easily write a new firmware.

Today I found a pair of scissors accidentally touching my board on GPIO pins, I immediately removed the scissors knowing it could potentially damage the board via short circuit. I removed the board from USB port and plugged it back. The application written on the flash is working correctly, it is a bluetooth flash button service, which can be controlled via Android app NRF Blinky. The diode can be controller correctly, it flashes upon command and also the button sends notification to my Android phone. So far it seems allright.

BUT, after I long press the reset button to enter bootloader mode, the diode does not glow read like heartbeat anymore, it tries to glow red and starts flashing red randomly like a current it flowing throught the diode randomly. Therefore I cannot write any new firmware to my board.

Moreover, I used to recover my dongle when accidentally locking my nrf52840 via OpenOCD, but right now, it cannot even connect to the device yielding:

Error: Error connecting DP : cannot read IDR

Does anyone know how to resolve this issue?

I suspect I damaged partially my board shortcutting it but I still wonder wheter there is a sort of a utility I can verify what is wrong exactly with my board. Just the bootloader might be corrupted but it is very suspicious that OpenOCD cannot communicate with the MCU via OpenOCD anymore.

Thank you very much

[Hung Bui]

Hi Ivo, 
Could you check your Jlink driver ? Here I found a similar report: 

 RE: Can't burn nrf52840 Dongle in Linux with nrfConnect v3.9.1 with Programmer v2.0.1 

But it still strange that you can do DFU with the OK one. 

I don't have an idea on what could be wrong here. I dont think the code or the hardware can detect any issue with the voltage or hardware to give you the LED indication. You can find the code of the bootloader in \examples\dfu\open_bootloader\pca10059_usb in nRF5 SDK. 

I suspect that it was not enough current/voltage to run the bootloader and it keep reset randomly and causing the LED to turn off and on. 

Please try testing the board in different USB port or on different PC. You also can simply test it with any USB charger or USB power bank , it should switch to DFU mode (growing LED) if it the hardware is still OK. 

[Ivo H]

I already tried different 5V power supplies with no luck.

Actually, I did not have any driver. I installed this: JLink_Linux_V770e_x86_64.deb, but the result is the

same.

Like I said, I managed to start the board twice with the LED glowing like in DFU mode, but I cannot repeat it, it was out of the blue, just a random success, so I guess there is something wrong with the current draw.

When pressing the button the diode starts the glow once but immediate turns to the random fast red blinking, like you wrote, it could be related to current draw when resetting all the time.

[Hung Bui]

I think it has some hardware issue. But I'm not sure if it worth it to go to the bottom of the problem especially when we have limited way of debugging this.

We may need to look deeper if the issue reproduced. But for now I would assume it got some damage either on the PCB or on the chip. 

If you want to debug this further I would suggest to solder the 10pin header on the P1 port and use a DK/programmer to debug it just like on a DK.