Accidentally input 12vdc into usb port of Photon 2, is it dead or can it be repaired? RGB will not come on, D7 light is on after switching power back to 5vdc, nothing else
It's almost certainly dead.
12V exceeds the absolute maximum input of the voltage regulator (recommended maximum is 5.5V, absolute maximum is 6.0V).
I would have thought it would have fried the regulator and it would be open but if you have D7 on, it's because there's a hardware pull-up so the regulator probably recovered, but during the over-voltage it let through greater than 3.6 VDC and that fried the RTL872x MCU.