you can use a 6 ch rx with a 4 ch tx.when you purchased the rx did you get one that is compatible with futaba?jr and airtronics use a different shift than hitec and futaba tx and they will not work.some rx a shift selectable with a jumper wire.usuall channels 1-4 are the primary flight channels controlled by the sticks.check by moving servo connecters to different locations incase this is different.try plugging a fully charged battery directly into the rx bypassing the swith in case it is bad.good luck