Chosen Solution
I got a device from a friend. The device didn´t start at all. Hard Rest…… Then I plugged a charged battery in and it booted to springboard. But the phone does not detect any USB connection. Even in DFU mode, my iMac doesn´t detect the phone. There were 3 missing caps near the battery connector. I replaced these. I checked the voltage on any component that is a need for USB detection and charging but all fine. In my opinion, the error should be caused by U2 chipset, but the voltage supplying this chip is fine and at the right value. Do you have any other ideas what could cause this problem? (no water damage, but he replaced his battery with a very bad third party battery) Thank you in advance.
As @benjamen50 suggests, changing U2 at this point is the logical thing to do. Even through the supplied voltage is correct does not mean that the IC is not defective. Remember that U2 is above all a communications IC, not a charging IC. If anything is wrong on the communication protocol lines, the phone will not recognize the battery or accessory and nothing will happen, including no charge. I’m also a little concerned about the missing caps. This could have been a simple prying error but it could be indicative of more damage, possibly caused by a really bad repair attempt. The poor quality battery could also have cause issues on the logic board. Do you know if your friend used original cables and chargers?
