Received message characters are wrong - but sent are right!?

Hello

I have an odd problem with an old Fasttrack modem I have.

When sending messages (PDU mode) some characters are coming out wrong, this is a problem since moving the modem from an old machine to a new one.
The characters concerned are:
“8” becomes an “i” with a odd point
“a” becomes an “a” with a line above
“n” becomes a “u” with 2 dots above
“s” becomes an “a” with a circle above
“F” becomes an “e” with a line above
“S” becomes an “a” with 2 dots above
“T” becomes an “e” with a line above

Any help will be greatly appreciated!

Thanks
Ivan