Home flex unresponsive, replaced multiple parts

So I repaired my xxx iPhone today. Noticed before I sold it, the home button didn't work.

So I ripped it back apart (not literally) and checked the flex. Had some corrosion, but wasn't much, so I just grabbed a new button, put it in the socket for the dock connector. Reset the phone and tried again with tr new flex. Didn't work. So I took out the dock connector and put one in from a working CDMA iPhone, connected it to the home flex in the phone, no go. Tried new flex. No go.

So with replaced dock connector and home flex ribbon. It must be the motherboard? I'm about to take some alcohol to it pretty soon. Maine something is just dirty. Any suggestions?

Btw I buy and sell iPhone on a daily. I've got quite a few lemons lol.