Flashing red (sos +1 = hard fault) cannot get to safe mode?

hi,
got a photon which was working fine for a long time. at some point it started flashing red (sos + 1 = hard fault) and now i am trying to recover. it will not go into safe mode. it does go into dfu mode (but i cannot seem to do anything with it). the other thing i noticed is that the rgb-led lights up blue in reset (do not think i have seen that before)
anyone any idea how to recover this one?
thanks

How exactly can’t you do anything with it? What have you tried?

i can make the photon blink yellow. i do see a device on usb (/dev/tty.usbxxxx) but:

thelema:~ frank$ particle flash --usb tinker

!!! I was unable to detect any devices in DFU mode…

Your device will blink yellow when in DFU mode.
If your device is not blinking yellow, please:

  1. Press and hold both the RESET/RST and MODE/SETUP buttons simultaneously.

  2. Release only the RESET/RST button while continuing to hold the MODE/SETUP button.

  3. Release the MODE/SETUP button once the device begins to blink yellow.

Error writing firmware…No DFU device found