Djoe:
Paul__B:
Not sure what you are describing here. The Nano is essentially a miniature version of the Duemilanove. It is true that if the FT232 chip was damaged it would not download sketches, but when you say "When I unplug the Nano board the USB is working fine", exactly what do you mean?I have build an board with sensors and power where I plug the Nano. When the Nano is plug and powered by this board the FTDI chip does not work. But when I unplug the Nano board and connect only the USB cable on it, all is working.
Well possibly you have a wiring problem with the board you plug the nano into, maybe trying to use pins 0 or 1? Can you post a schematic drawing of the board you are plugging the nano into?