Single byte memtest errors — possible to tell which RAM chip is defective? I'm running memtest on a 2014 MacBook Air 11" with 8 GB memory spread over 4 Hynix chips. 

I'm getting errors in the most significant byte of every (eighth) memory address when running memtest. After a while memtest just stops saying "too many errors occurred" (that's a nice line from an error testing utility ) so I don't know the extent of the error, nor do I see how I could find that out with a memory tool that repeatedly stops after ten minutes. 



Is it possible to narrow down which hardware component is probably faulty from this information?
Not from that utility.  You’d need to see how the chips were laid out and what the addressing scheme was.  Since Apple doesn’t provide this, you’d be guessing.

Since these chips are soldered, they can’t be (user) replaced unless you take it to a shop that does SMT rework.  

Keep in mind it could also be the memory “controller” that handles the addressing of the memory that’s has also failed.  Usually when this work is done, all chips are replaced.