Not a good idea to mix sets, even of the same exact model, generally if they don't want to play you can get them to with slight voltage adjustments, which wouldn't really be the case here as these are at 1.65, which is really suggested for 1600 sticks....JEDEC standard is 1.5, 1.65 usually doesn't come into play until 2133 and above....it's often a sign of weak ICs (memory chips) with 1600 sticks