NASLite Network Attached Storage

Further to previous question, I am trying to backup the four drives in my NASlite server to an external drive connected to a raaspberry pi. I'm using rsync to do this, which basically works well. For a few file names which have non standard characters I get an error:

Invalid or incomplete multibyte or wide character

and those files fail to copy.

When I try a similar rsync to an ubuntu machine I get a ? character in the file name and "invalid encoding" appended. when I browse to one of the "corrupted" files in a windows share from same laptop, the file name appears correctly. The same file don't display a missing character when browsing the server via my browser (http).

I've found various sites discussing similar things being an encoding issue and possibly i need to use convmv to re-encode the file names. I have no idea when it comes to filename encoding. How do I find out what encoding is used on the files that fail? What should I convert them to? How can I run this on files on the server?

Thanks for the help!

Andy