[Kenwood] ts2000 interface

[Kostas SV1DPI]

I build a simple interface for a friend's ts2000 (to connect the soundcard, 
ptt, cw, fsk).
My interface is simple with a resitor and an optocoupler 4N37.
I made the connections to acc-2 and cw as the manual says. ptt, cw and data 
in/out work like a charm. But the fsk doesn't play (i listen a steady tone 
in monitor, not diddles).
I checked that
the com port is ok
4n37 works as i have a led in serious and lights with the right rythm
Any menu to look for as my friend doesn't know the radio quite good, or any 
other things to check?
Tnx for the help in advance
Kostas sv1dpi