Tillers

I have a Husqvarna rear tine tiller. While tilling by neighbors garden I hit a tree root. The gears all work but the tines will not turn. I took it to a repair shop. and was told that the transmission was broken and would cost around $700. it would be cheaper to buy another one from him. My question is that I checked the tiller and it would go into forward and reverse with out any problem. If this is the case how can the transmission be broken. He also told me on the phone that maybe the chain was broken.