Why is my iPhone not responding to charging?

I've tried to charge my iPhone once with an unauthorized cable, it didn't charge and after that I couldn't charge it anymore not even with an authorized cable. Eventually the battery ran out and I couldn't get the phone to power on anymore. I took the device to an authorized Apple provider shop and the technician opened it and tried to power on with a different battery to no avail. He said that it's probably the logic board. What could be the cause of this? And if it is indeed the logic board that is defective, is there any way to save the data?