Only charges through a USB port and not an AC block

I work for a cell phone and tablet repair company. I got an iPad mini in the other day that would not turn on. I tried to charge normally and it didnt take a charge at all. Then I also tried to connect to iTunes and the PC would not read the device. So I soldered a new charge port to the logic board. Now I got it to charge, but ONLY through my USB port. It will not charge on an AC block. Any ideas as to why this is or how to fix it?

Thank you in advance

JJ