Is there a problem with the motherboard?

I bought a defective iPhone. The phone is totally broken and I'm going to fix it if there's nothing wrong with the motherboard. It's iCloud locked and I could get the apple id credentials but I can't put them in because it doesn't connect to the internet or can't find the internet. I changed the wifi cable, it didn't help. the gps antenna is completely broken and I haven't tried to replace it yet. could it be that the phone starts working if I change the gps antenna? So is there something wrong with the motherboard?