5 wires lead from 2 breakers to the hot tub board, one of them is completely fired,do you think I can just replace the wire or do you think it is the board?

If one of the wires is fried at the board it may have been caused by a loose connection. Without physically seeing the board the question of replacing it can not be answered.

Definitely a loose connection, If you cannot do a repair or "outboard" the connection, you may need a board, any bad connection or splice will heat up and fail again.
"Loose connections Generate Heat"