D7 is in the VCC line right next to the relay K1.
Check your wiring. It seems likely that you applied
12v to the Nano (or reversed the polarity), which probably fried it.
If K1 coil is open, then the 12c would be applied
directly to D7 as the load at that point. Maybe that's
what took out the diode...
john
AD5YE
