Dish box is connected to RCA with HDMI or AV?
If HDMI then the problem may be in the box or sound system. If AV then you may have a bad cable.
Does changed it mean you tried a different Dish box? A different cable?
What is only making sound on one channel? The speaker in the RCA or something else? Does the RCA have two speakers? Does the "something else" play both channels with source other than the Dish box?