After an attempted reset today using the RESET push button, my Photon has become totally non-responsive. Using USB power, I measure 5V at the VIN pin, 3.3V at the 3V3 pin (regulator still functioning), and 3.3V at the RST pin (as expected). No main LED, no light on D7 (~0.25 V), no USB serial connection. No response to either the RESET or SETUP button in any combination.
My first thought was that an iffy power cable connection may have caused a low voltage condition, detailed elsewhere. I attempted to repair the bootloader using the Embedded SWD tool (https://github.com/m-mcgowan/embedded-swd), but I get either no device detected or SWD protocol error (even after double checking the wiring). Also, when I connected the D7 wire from one device to the other, the D7 LED on the first device went dark.
Any other thoughts of parts of the device to check over, or ideas on what may have died? I don’t want to believe it was ESD, but it’s always a possibility. Maybe something else was shorted before the reset and I didn’t notice?