A:Answer I purchased and added a stick of 8GB DDR4 2666MHz PC4-21300 Unbuffered Non-ECC 1.2V CL19
This is working well for me, including for gaming. I won't claim this is the only memory timing/spec that will work or even the best, but it is working for me and matches the info on the stick that was in my 690 Pavilion when I got in to add the memory.