sound decoder for 121 class loco problem

[controller]

Hi, I have just replaced a sound decoder in a 121 class loco. Everything is working fine except the direction of travel. They either come towards each other or travel in the opposite direction to each other. 

I am using a Guagemaster Prodigy Advance controller, DBLHEAD, add second loco, change direction etc. I have tried this several times, but without any luck. I don't want to start messing with CV29 unless I have to. Any help from you gentlemen would be appreciated .

 

Thanks,

Controller.