W520 mem above 4gb fails in 1 slot only

[cnbenson]

I have a dual core w520, originally with 2x4gb. I'm trying to upgrade to 2x8gb, but 8gb dimm fails in one slot, but not the other. Same behavior with both dimms. Errors reported with memtest86 and WMD. Memtest reports different cas timings when same chip is in different slots (lower in the slot that fails).

Any ideas on why this is failing?

[richk]

Which slots are you using?  You need to use one slot under the keyboard and one on the bottom.  On the top (under the keyboard), use the upper slot, and on the bottom, use the one on the left (if I remember correctly).

[richk]

Which slots are you using?  You need to use one slot under the keyboard and one on the bottom.  On the top (under the keyboard), use the upper slot, and on the bottom, use the one on the left (if I remember correctly).

[cnbenson]

Only two slots are usable (the other two have do not use cards in them) - this is, as I understand, how the dual-core model works.

So, I started with 2 4gb cards. I removed those and replaced with 2 8gb cards in same slots. I had a bsod under normal usage after about an hour.

Used memtest to check both cards in each slot (rotating). Both cards show errors when in bottom slot, but not in top slot. I thought perhaps slot bad, so I put old 4gb back, ran memtest again, but no errors. I get errors only when card in bottom slot is over 4gb.

The only other thing I noticed is memtest reports different cas timings for the same card when in the problem slot vs the ok slot.

[richk]

What model/brand is the memory you are using?

[cnbenson]

Crucial 

[richk]

That is the wrong memory for the machine.  You bought 1.35 volt DDR3L and you need 1.5 volt DDR3.  It will not work reliably

[cnbenson]

Crucial support is telling me "DDR3L is variable, self regulating memory and it will run up to 1.9 volts if the system requires it." Is this a known thing with the W520?

[richk]

If it will work at 1.5v, then I have no suggestions.  Sorry.

[cnbenson · Accepted solution]

In case anyone should find this and have had a similar issue... updated BIOS to latest version and performed hard reset (unplugged internal battery for a bit) and issue went away. Tech from Crucial thought BIOS may have been having trouble with something about the newer memory.