If you have access to the dealer site it is available for download.
Your power standby command is correct.
Make sure that you are not in hex entry mode when entering the 232 command into the RTI 232 window. Make sure your Baud rate and Parity settings are correct.
Do not use a null modem adapter or extension cable.
Make sure a ground wire is connected from the RP6 ground terminal to the phono ground lug on the receiver OR to another positively grounded point. You said the ground wire was connected to the bottom of the receiver. Are you sure you are making good contact?
Make sure you Power the receiver on Manually first and then issue an off command via 232
If you follow these steps it should work fine. If you followed them correctly and it does not work perhaps there is an equipment issue with the receiver or the RTI gear.
These issues are discussed in this post.
[Link: remotecentral.com]