Phone won't charge but reacts to USB

Hi everyone!

I bought a bunch of old phones from eBay and I’m having trouble troubleshooting this one.

The Problem: The Phone won’t neither charge nor be recognized by iTunes. Windows detects it when plugged in, but states “USB device not recognized“. The phone anyways turns on, when being plugged into a charger or computer. It pulls 0.04 Ampere from the charger.

Strange thing: The seller charged the phone 100% before shipping it and it still is at around 90%. Phone wasn’t opened before as far as is can tell.

What would you guys check next? I’ve got tools, multimeter, etc. so I’d like to test a bit, before I just order a new Dock connector.

Thanks in advance, cheers,

Sebastian