Balboa does not provide schematics about their circuit boards to anyone. They also do not supply parts for items used in their circuit boards, Thus it is not a matter of the cost to fix a circuit boatd, but a matter that it is no economically feasible, if you consider North American shop labour rates to even attempt to do so. Your only choice if you are looking at the dollars is to simpy replace the circuit board.
Your next step would be to find out what circuit board you have and whether it is stil in production. The circuit board serial # is usully found on a white label stuck to the transformer. its a 5 digit number followed by a - and then a lenghty set of numbers. If you let me know thisserial number I can advise you whether to persue obtaining the replacement board or whether it will be cheaper to buy a complete new spa pack.
Dieter Jung
Northern Lights Group