Do you have a pin-out or a test point? I have a scope and can check it out. If I upload a scan of the board can you point it out?
See the capacitors labeling? Alot of them to smooth out the ripples.
I think the problem is, not fully dead, if fully dead, easy to find, half dead is more difficult.
Trace it when the mac is doing some dynamic activity, not static.
Its easy to say scope it until you actually do it, it's smd.
For the pros, they will put a DDR3 dummy loads onto the bank using dummy DDR3 fixtures.
If it's too difficult, just look for them. cheers!