Dave, thanks for your reply. My RX is a JR RG812BX. The Xbus channel label is on the Aux 3 channel on this RX, i.e. channel eight. There are no other marked Xbus channels on the RX are there? I'm confused! Also I thought Mode A was only for JR 'add ons' such as an XPort Duo XBI-14DRS. Other brands such as a Powerbox expander were on Mode B? Am I wrong please? If I plug a servo into channel eight it shouldn't work if it is set as an Xbus channel should it? I'll try it on Mode A when I get home. Also does anyone no the frame rate for Savox servos? The default in the software is 16, but they say in the Powerbox expander instructions that most servos are 20, so that's what I have it set at. Regards Murray.