My A4000 motherboard and 3640 are with Acill right now being treated for these same symptoms. I had assumed they were caused by damage from a capacitor leak on the motherboard rather than the CPU board. Will report back when I have a diagnosis from him 
Yup, things are slow and my normal full time job is sending me all over the dang place! Hope to have these done soon.
Usually, it is the CPU having eaten traces from the caps. The 3640 is famous for killing itself due to them reversing caps from the correct polarity during manufacture.
