PCA10056 Not working

[vishal.roy]

Just bought 2 nrf52840 DK's both stopped working

Observation

• Was able to program and run SDK examples.
• Above working setup not disturbed,so all cables are in order verified that
• The current problem i have:
  1. when I connect the DK to PC the device is not shown in device manager initially.After awhile it pops up
  2. When I try to flash it fails and LEDs switch of and come back up.
  3. The board had the blinky example code.So if from Step 1 I toggle IF Boot/Reset switch I can see the UART logs in terminal.
  4. Very weird observation is there is buzzing sound coming from the board.Can i do something to fix this issue.
  5. When I go near the switch usb/VDD/Lipo selection the entire board switches off and comes back up as a move my hand.Attached video.The buzzing sound can be heard in video
•  

[Simonr]

Hi

I got an update today from one of the developers of the nRF52840 DK. The VIO_REF has a 10 MΩ pull down resistor (R88) which is set to high to get a minimal leakage when supplying the nRF52840 directly from P21, as this also connects on the same net. However, it seems like the pull resistor is too weak, so when touching the pin the voltage rises slightly over the point that the "voltage follower" trigger. This will then supply this 0.8V to the circuitry and the board will be reset. Our suggestion is to lower R88 to 1mΩ and see if the issue is still there. If it is, tryk 100kΩ.

Best regards,

Simon

[vishal.roy]

Sorry for the late reply.

Have couple of demos planned with this board. Have raised an RMA for this board. Once  I get the replacement will definitely try the fix on the defective one and give you my feedback.

Just out of curiosity have you recreated this issues. Do you think the pull resistor is too weak by design or it is damaged during production causing a higher resistance path. If by design it is weak and requires a bit stronger pull up yeah 100kΩ makes sense if not I could replace the resistor with another 1mΩ.