Photon 2 shows no USB activity on a computer (no enumeration, no DFU lights) but charges fine on a wall adapter.

Hardware
1

Hi all, hoping someone can help me figure out if this is a dead board or something fixable.

Background: This board worked fine when I last used it (coding/flashing over USB) over a year ago. It's been sitting unused since then, and now it won't enumerate at all.

Symptoms:

  • When I plug my Photon 2 into a wall USB power adapter, I get a steady yellow LED at the USB connector — so the board is powering on fine.
  • When I plug the exact same board into a computer via USB, there is zero LED activity of any kind — no yellow, no blue, nothing.
  • This happens across two different computers (Windows and Mac), multiple USB cables, and multiple USB ports on each machine.
  • I don't see the device show up anywhere — no COM port in Windows Device Manager, and particle list shows the device as offline.
  • I tried forcing DFU mode (hold RESET + MODE, release RESET, keep holding MODE) while connected to a computer — still nothing, no lights at all.
  • LiPo battery is disconnected, so that's not a factor.

What I've ruled out so far:

  • Cables — these are the same cables I used successfully with this exact board over a year ago, and they still charge other devices fine now (though I don't have another data-capable device to confirm they still pass data)
  • Ports/computers (tried multiple of each)
  • Drivers/permissions (checked Device Manager and Mac privacy settings)

This really looks to me like a hardware issue specific to the USB data lines rather than power delivery, but I wanted to check with the community before assuming the board is dead. Has anyone run into this exact pattern before, especially after a board's been sitting unused for a while? Is there a way to confirm it's a USB data-line fault, or any other test I should try before giving up on the board?

2

That appears to be a hardware failure.

The yellow light next to the USB connector is a charge LED, and is controlled by the battery charger chip, not the MCU. So that can work as long as there power on the USB port.

The MCU and other LEDs are powered by the 3.3V power regulator, which can be powered by USB or battery. I'd guess that the 3.3V regulator failed. It's possible but less likely that it's the MCU that failed.

If the MCU cannot power up, computers may limit the USB port to 100 mA, which is not high enough to charge, so that's not a complete surprise that the charge LED does not come on in this case.