Thanks for advice and links (i already looked at this ch340 datasheet but it's very short and incomplete -no data about 3v3 output voltage interval)
I've got something : only 36ohms between gnd and 5V, more than 1Kohm on a spare nano, no output data shorted to gnd or 5V
BUT only 6ohms between REF and gnd (about 3K on my spare nano) And REF pin is shown unlinked on Raduino board ->
- bad nano PCB with no space between gnd and ref
- short circuit on capacitor on the REF pin
but all that hard to check and correct without unsolder :-(
first easy thing that i can do easily is cut pcb between Atmega pin 21 and REF output of the board (but i will need later to replace the capa on the other side to enforce noise reduction on analog read)
second thing is to cut and remove this unused pin between nano and raduino (in case the short circuit is on the raduino solder part)
i will keep you informed
73 - Remi
