Ape

Hello guys! I bought a used Balboa spa pool. Previous owner said that the fixing price would be very expensive but I wanted to take the challenge. Obviously there was something wrong because nothing happened when I powered on the system. I opened the case and motherboard was broken. The was clear mark where the folio had burned (attatched picture). I fixed the burned folio by tinning it and everything looked good, after I tinned the board I wanted to make sure everything is right, local electronics repairman checked the system and said that everything is fine on motherboard. He couldnt test board with 3-phase but tested all phases without problems. I noticed that the motherboard had problems because previous owner tried to attatch 3 phase power and didnt disconnect all the wires correct. Now I tried to attach motherboard to pool and I connected all the systems on their right places. My house burns fuse when I plug power on to the board. What should I check next? Sorry for long story but hope you can help me. Ape from Finland