awhile back i fried my nano on of all things an infrared project and have not been able to program it with usb (though i assume iscp would still be an option considering external power still works). but recently ive been doing some testing and i discovered that d1 (a schottky diode) was not allowing the usb voltage to pass. anyway i was assuming that this diode protects the usb bus from external power through the regulator and that the schottky diode was chosen for its lower voltage drop. so i was wondering if these assumptions would be correct and if it would be ok to replace it with a regular diode or perhaps just a jumper that i can remove while programming it.
anyway i was assuming that this diode protects the usb bus from external power through the regulator and that the schottky diode was chosen for its lower voltage drop. so i was wondering if these assumptions would be correct and if it would be ok to replace it with a regular diode or perhaps just a jumper that i can remove while programming it.
Your assumptions are correct. and yes, a standard 1 amp diode would work but would lower the voltage some compaired to a schottky.
Any one amp (or higher) schottky didode should be the first choise and they aren't that expensive or hard to find.
http://www.allelectronics.com/make-a-store/category/205/Diodes/1.html
Looks like Diode is to keep external 5V from going back into the USB port.
If its open, then jumpering around it to download sketches would be okay while external Vin is not applied.
From the schematic & board files, looks like
SOD-123 package
MBR0520 value, should be easy to replace with a little care.