I would 1st make sure that the RS232 parameters for the TVS50 are indeed at default. 9600, 8, N 1
Do this in the TVS 50 by setting dip switch 1 to on and the others should all be off. Unplug the TVS50, wait a minute or 2 and plug it in.
Give it a few minutes to boot up.
What system is this connected to?