iPhone 5 no service or no signal.

I had a iPhone 5 with liquid damage. I cleaned all the corrosion and the phone worked all fine.

Now after 5 months the phone doesnt find any service or signal. tried resetting the network settings, new software, used different sim cards

tried another antenna cable ( dock connector )even used another back case. imei, baseband all ok. date, time ok.

My question is which components do i have to troubleshoot so i can find a solution. Which components or ic's is related to no network, or no service. I got a scrap iphone 5 motherboard were i can take out components. Got the necessary skills to solder. got also the schematics.

Hope you guys can help me out