PaulS:
but if I try with a serial port monitor to send 01 73 HEX it reply me!
Which Serial Port Monitor? Post a screen shot of before the send and after the send (the reply).
It's possible that your understanding of what the scale expects could be all wrong. Perhaps it IS expecting "01" and "73", not 0x01 and 0x73.
I have tried wit more and with all work well. Now I use a demo version of Eltima software Serial port monitor 4.0, here you can see a screenshot where with the Serial Port Monitor software I send a string to the Arduino and you can see the string in the Arduino serial Monitor.
After this I think that Arduino and RS232 shield are right connected!
I think that it ll be a problem in the sending or in the reception of the string
thanks for your support
Fabio