GA-Z68MX-UD2H-B3 and 16GB F3-12800CL9D-8GBSR2 (x2)

[Signal]

I'm having trouble getting stability with F3-12800CL9D-8GBSR2 x2 kits for 16GB (x4 sticks total) at 1600 in a Gigabyte GA-Z68MX-UD2H-B3. I'm using a 2600K CPU in this setup.

Using any combination of x2 sticks in either DIMM slots 1&2 or 3&4 work fine using profile1 XMP settings.

When I add the extra pair of sticks, I start failing memtest86+ v4.20 tests.
It goes up to the tail end of Test #5 [Block move, 80 moves] and starts dumping errors consistently at that point. Multiple tests and moving the sticks around always results in the failures at the same place.

I tried changing the timings to 9-10-9-28, bumping the QPI/VTT voltage to 1.1v, and the mem itself to 1.3v (these are low voltage 1.25v spec dimms).

I'm not OC'ing anything as I want simply stock speed and stability at this point.

Any other ideas??

[Tradesman]

Check that you have the latest BIOS, and XMP won't work with two sets, so will need to input timings manually and may have to raise DRAM and/or VCCIO voltage slightly ( + .05 or so)

[Signal]

Yes, using the latest bios.
Have turned off XMP profile and manually set the timings back to 9-9-9-24.
Have tried bumping the VTT and DIMM voltages to various degrees without going crazy.

The only thing that has made a difference so far is turning off "Rank Interleaving".
I end up with a couple of errors at the same point in memtest vs. hundreds of errors, but still not error free.

[Signal]

I just let it go through the full test and let it start pass 2.
It failed with 10 more errors at the same place.

I would think that would indicate bad ram or a DIMM slot, but have tested combinations of pairs of sticks in either DIMM channel successfully.

[Tradesman]

As a test try with your CPU multiplier at 36 or 37 and see what it does

[Signal]

Same results with the multiplier change.

I moved the mem and cpu to a MSI z68ma-ed55 and it tests fine there at 1600 with no futzing.
Got through 3 memtest passes with no errors.

I put an i5 2400 in the gigabyte and same errors.

Trying to compare the settings between the two boards.

[Tradesman]

Sounds like the GB mobo may have a problem. It's nice to have a few other parts or another rig for testing purposes, isn't it? Most would have just RMAed the DRAM and still had a problem after the new sticks arrived.