This sounds like a baudrate problem, try the following
Baud rate 19 200.
In [PABX3 -> OPTIONS -> COMMUNICATION], baud rate.
ALSO SEE: I get "garbage" in VT100 in PABX3 or no data.
Please note: The UTMs buffer can only handle the following
baud rates 300, 600, 1200, 2400, 4800 and 9600.