Make sure your CM232 is plugged directly into the RP6 and not into one of the IR adaptor cables. Also try connecting the CM232 into the CAV instead of the tuner, the rnet should carry the rs232 through to the tuner, this will test to see if it isn;t a bad rs232 port on the tuner. Also try different source commands for maybe tuner being source 1 or 3, you never know, it is always possible the RP6 or ST2 are bad, I would try RTI Tech support, they may have a different insight into the problem.