Possible hardware issue with nRF52840-DK power source switch or onboard debugger

[yangtw]

Subject: Possible hardware issue with nRF52840-DK (PCA10056) power source switch or onboard debugger

Hello Nordic Support,

I recently received a new nRF52840-DK and am experiencing intermittent power and USB detection issues.

Board Information

• Board: nRF52840-DK 

• Operating System: Fedora Linux

• Board is completely unmodified

• No external circuitry is connected

Symptoms

1. The board is sometimes detected by the PC as:

SEGGER J-Link PLUS
USB ID 1366:0101

and sometimes it is not detected at all.

2. The behavior appears to depend on the Power Source switch position.

   • When set directly to USB, the board often fails to start properly.

   • The VBUS LED becomes very dim or almost off.

   • The board is not detected by the computer.

3. When the switch is moved to VDD, the board usually powers up correctly.

   • LEDs become brighter.

   • The board is detected by the computer.

   • SEGGER J-Link appears in lsusb.

4. In some cases, after successfully powering up in VDD mode, I can switch the Power Source back to USB and the board continues operating normally.

5. The board may run for some time and then suddenly stop responding or disconnect from USB.

6. I have observed intermittent LED flickering. The power indicator occasionally becomes briefly dim and then returns to normal brightness.

Troubleshooting Already Performed

• Tested multiple USB cables.

• Tested multiple USB ports.

• Verified that Linux can sometimes detect the onboard SEGGER debugger.

• Verified that the onboard debugger firmware is at least partially functional because the board is occasionally recognized as a SEGGER J-Link device.

• No external hardware is connected.

• The board has never been modified.

Additional Observation

The board appears significantly more reliable when first powered in VDD mode. Starting directly in USB mode often fails.

Because the behavior changes depending on the Power Source switch position and because the VBUS LED brightness changes noticeably, I suspect either:

1. A faulty Power Source switch.

2. A power path issue between USB VBUS and the board power circuitry.

3. A problem with the onboard debugger power domain.

Could you please advise whether this behavior is expected, whether there are known issues related to the Power Source switch, or whether the board may be defective?

Thank you.

[yangtw]

I'm sorry, but I've found that many things are unpredictable. Sometimes the VDD works fine, and sometimes the USB works fine. I think it's not just a problem with SW10.