nrf52840DK is not getting powered up

[jeevan t raj]

Hi,

We have a strange issue. We have got two nrf52840DK(PCA10056, 2.0.0, 2019.47). The nrf52840DK board is not getting powered up after the board rested in off for a long time say 2 days. when USB is connected no LED is turned ON, JLink drive not detected on the PC. I ensured that the USB cable using is a good one and the power source selector switch is in the required position. In this state, I can hear a feeble buzzing sound from the board(Guessing from any of the inductor is creating this sound). I had tried to connect a power supply of 3v to the External supply provision near the LiPo battery connector instead of powering from J2 USB. But still, no response received from the board. If the board is kept in a powered position for some time say 4 or 5hrs, then it starts to power up and works as usual. We have 2 52840DK's available. Both showing this behavior. But we have one nRF52832DK(PCA10040, V1.1.0, 2016.32), no such issues were observed on this 832DK. 

Please suggest possible ways to get rid of this issue.

[Amanda Hsieh]

Hi Jeevan, 

Please check that SW6 is on the DEFAULT position and SW9 is on the VDD position as the figure. 

 

Let me know this can help or not. Thanks. 

-Amanda H.

[jeevan t raj]

Hi Amanda,

Yes, SW6 is in DEFAULT position(Right)  and SW9 is in VDD position(middle).

[Amanda Hsieh]

Hi Jeevan, 

Could you have some voltage levels on some testpoint when it is in this "limbo" state?

It would be interesting to see the voltage on:

• TP28
• TP36
• TP29
• TP35

Maybe you could try to short TP33 to GND briefly and see if that "jump starts" the board. 

-Amanda H.

[jeevan t raj]

Hai Amanda,

Thanks for the reply.

Today morning also had the issue. I kept the board powered ON from the morning. By around 1 pm, it turned up and started working as normal. Still, now I am working on it. 

Most probably I shall get the issue tomorrow morning after the board rested completely for today's night.

I will try the probing and shorting as you said and inform you about the readings/observation.

[jeevan t raj]

Hi Amanda,

I had probed the TP's. The voltage is found fluctuating, not a constant value.

TP28 -    3.3 - 3.8v
TP36 -    3.3 - 3.9v
TP29 -    1.2 - 1.7v
TP35 -    0 - 0.2v

When I shorted the TP33 to the GND board started up immediately and working properly. But when I removed that jumper wire it turned back to off. 

[jeevan t raj]

Amanda, 

Adding one more observation.

Even the board turned ON gradually, the voltages are found changing in TP 28, 36, 29. But the TP35 now measures 1.2-1.5V

[Amanda Hsieh]

Hi Jeevan, 

There is something strange here:

• TP28: This should be USB voltage minus a small diode drop, so ~4.5V
• TP36: Is on the output of the boost regulator, so this should be 5V
• TP29: Is the output of the buck regulator and the "VREG enable" load switch, this should be 3V
• TP35: Is the power to the Segger, this should be 3V.

It's hard to say exactly where in the chain things go bad since it is the same behavior when powering externally, but that it works when TP33 is grounded it leads me towards issues with the voltage follower. 

Grounding TP33 is not a problem as long as the SW9 is in the VDD position, any other position would then short the VDD_nRF to GND. A better alternative would probably add a pull-down to TP33, 1MOhm or 100kOhm.

-Amanda H.

[jeevan t raj]

Hi Amanda,

Thanks for the reply. It really helped. We will take care of the pull-down as you mentioned.

I can continue the development activities by doing this workaround in my DK.