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Cannot achieve 2666MHz Memory Speed


MRig
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Hello,

 

New to this forum...

 

I built my rig in 2015 and originally had 2x4gb of Corsair Vengeance LPX CMK8GX4M2A2666C16. I upgraded it with another 2x4gb in November of this year.

 

When my system had 2x4gb it had no problem going up to 2666MHz via the XMP profile on the BIOS. Now, with an extra 2 sticks of the same part number, it will not budge from 2133MHz.

 

I have tried troubleshooting by adding 1 stick at a time of ram and rebooting... With 3x4gb sticks, the XMP profile works as intended and I have 12GB of 2666MHz memory. Then, as soon as I add the last stick into the fourth DIMM slot, it changes back to 2133MHz.

 

Is this indicative of a faulty DIMM slot? Or do I need to increase voltages or something?

 

Any help would be greatly appreciated.

 

Specs:

CPU: i5 6500

MOBO: ASRock z170 Pro4s (w/Latest BIOS 7.50)

Memory: 4x4gb Corsair Vengeance LPX (running at 2133MHz :(:)

GPU: Radeon R9 380

Case: NZXT S340

PSU: EVGA 750W G2

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It's could be an issue of two sets that won't work together. This is not unheard of.

It's also possible that 4 sticks of 2666 is just a bit too much for the 6th gen/Skylake memory controller. The max officially supported speed is 2133 - anything else is an overclock. So that's also quite possible.

 

To validate:

Put only the two sticks from the new set into the appropriate dual-channel slots. Set XMP for 2666. Do they work?

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Thank you for your response.

 

It's could be an issue of two sets that won't work together. This is not unheard of.

It's also possible that 4 sticks of 2666 is just a bit too much for the 6th gen/Skylake memory controller. The max officially supported speed is 2133 - anything else is an overclock. So that's also quite possible.

I see - this is a shame if so, maybe I am just going to have to resign to having 2133MHz memory until I upgrade my system.

 

To validate:

Put only the two sticks from the new set into the appropriate dual-channel slots. Set XMP for 2666. Do they work?

I have just tested the 2 new sticks in dual channel and yes, they are running at 2666MHz.

 

I guess another question is: Is there any way around this, at all? It just seems a shame that the XMP profile works for 3x4gb sticks but not the fourth stick.

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Well, it's sounding more and more like it's the IMC or possibly the motherboard that can't handle it. Still, it could be that both sets just don't play nice but if 3 work, I'd think that all 4 should also - assuming that the CPU and mobo can handle it. Not sure what else you could do, tbh.
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You may very well be able to run 2666 with the mixed kit, but you will need to manually set your primary timings and voltage. You can't use XMP with mixed kits. The preset has to match on every stick and that usually includes a specific number of modules.
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No, it's like any other overclocking method. Each specific hardware set-up has its own tolerances and you have to explore. However, the place to start would with the designated XMP values applied manually.

 

2666 Frequency

CL 16

t(RCD) 18

tRP 18

tRAS 35

 

DRAM voltage 1.20v, although you might need 1.25 to be safe on a mixed kit.

 

VCCIO and VCCSA voltage - some boards will auto set this to stratospheric levels. It's OK to start with auto on both, but if you are freezing on the desktop or getting a locked black screen, they may need tweaking. There are also motherboard specific guides out there and the terminology or labels used are often brand specific.

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No, it's like any other overclocking method. Each specific hardware set-up has its own tolerances and you have to explore. However, the place to start would with the designated XMP values applied manually.

 

2666 Frequency

CL 16

t(RCD) 18

tRP 18

tRAS 35

 

DRAM voltage 1.20v, although you might need 1.25 to be safe on a mixed kit.

This is great, thank you - I'll give it a go.

 

VCCIO and VCCSA voltage - some boards will auto set this to stratospheric levels. It's OK to start with auto on both, but if you are freezing on the desktop or getting a locked black screen, they may need tweaking. There are also motherboard specific guides out there and the terminology or labels used are often brand specific.

Thanks again, I'll report back with how it goes!

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