Chip no longer accessible after first successful connection and flash attempt

RE: Chip no longer accessible after first successful connection and flash attempt

DenDanne — Thu, 09 Jul 2026 16:04:23 GMT

Hi. Thanks for the help.

I am now able to get contact and flash the chip.

What solved it for me: DCC capacitor should not be there! I removed it so that DCC is floating (well its obviously not; there are as you said, components inside the module itself).

I kept the DEC4 capacitor.

Thanks again

RE: Chip no longer accessible after first successful connection and flash attempt

Kenneth — Wed, 08 Jul 2026 10:08:40 GMT

I can see various capacitors that is new to me, how and where did you find this?

The schematic needs to follow one of these:
https://docs.nordicsemi.com/r/bundle/ps_nrf52805/page/ref_circuitry.html

Since you are using a module I expect some of these components may be on the module itself. Make sure to follow the guidelines of the module manufacturer when it comes to external components.

Kenneth

RE: Chip no longer accessible after first successful connection and flash attempt

DenDanne — Wed, 08 Jul 2026 09:12:42 GMT

Hi, here is the schematic again:

I will try what you said when I get home

RE: Chip no longer accessible after first successful connection and flash attempt

Kenneth — Wed, 08 Jul 2026 09:08:26 GMT

Hello,

It doesn't seem as the schematic was uploaded, but if pulling RESET high doesn't work, then it may be related to firmware try to enable DCDC, but there is no DCDC circuitry mounted. The only way to get out of this situation is following this: nRF52840 stuck after programming Be extremely careful, you can easily damage the chip when you apply voltage directly to DEC4.

Kenneth

RE: Chip no longer accessible after first successful connection and flash attempt

DenDanne — Tue, 07 Jul 2026 15:53:46 GMT

Just to add some information.
I am probing SWCLK and SWIO pins on MDBT with oscilloscope.

As you can see, there are definately data transmission (but could be just one way of course).