Memory OC used to work but won't POST anymore

[Acme]

Hello

 

Long time fan of LTT and lurker on this forum, so sorry for this being my first post.

 

I have this weird issue with my RAM and can't figure out how to fix it, if it's even possible.  Long story short, this is a 2 years old build, i7 8700K @ 49 Ghz all cores, 64 GB Corsair LPX 3000 Mhz (4X 16 GB), Asus Z370-E Gaming and some other non significant stuff for this specific issue.  I used to run XMP 3000 Mhz profile on this setup without any issue.  And I can't anymore. At some point 2 weeks ago I had to investigate a boot issue and in doing so I "played" with the DIMMS.  At one point, one DIMM wasn't inserted correctly in the socket and I had POST failed on RAM test.  I then pushed the DIMM all in, and it posted.  At that moment I was running with default BIOS setting, no XMP, no OC (RAM speed on auto).

 

My initial problem being solved, I tried to go back to my OC profile, and the PC couldn't POST and failed the RAM test.  I then went into some "intense" testing and came to the conclusion that:

• Any RAM OC (i.e. over 2133 Mhz) will result in POST RAM failure with 4 DIMMs in (all 64 GB)
• OC @ 3000 Mhz is possible with only 32 GB (2 DIMMs) in either banks, with whatever DIMM combination
• So, it's not a specific socket
• And it's not a specific DIMM
• AND BTW I tried to push more voltage in (over 1.35), it didn't help.

So, I'm flabbergasted.  I also tried to OC manually, didn't work.  Same result.  Anything over 2133 Mhz will result with a POST RAM failure.

 

@2133 Mhz the PC runs fine without any issue and is as stable as it was, but I'm bummed I can't run with my RAM at full speed, at least not with 64 GB (and I need the full 64 for work).

 

Any ideas on what could be the issue?

 

TIA

 

 

 

[Haro]

well 4 16 gig sticks are a lot of pressure on the imc. 

you could try setting the vccio and sa to 1.1-12 and try 2666 with xmp on, if it boots use memtest or/and OCCT and check if it's stable.

and make your way up to 3200. 

Edited August 9, 2020 by TofuHaroto
stupid typo.

[Acme]

37 minutes ago, TofuHaroto said:

well 4 16 gig sticks are a lot of pressure on the imc. 

you could try setting the vccio and sa to 1.1-12 and try 2666 with xmp on, if it boots use memtest or/and OCCT and check if it's stable.

and make your way up to 3200. 

Thanks for taking the time.

 

Tried to up the vccio and sa to 1.1 or 1.2 with a pretty basic 2200 Mhz manual "OC" and very loose timings (and 1.35V on memory), it didn't even POST at all.  I can't figure out how I can manually set it to 2133 and it's all fine but as soon as I go one step over that, POST fails immediately. Makes no sense.

[Haro]

16 minutes ago, Acme said:

Makes no sense.

Wait so you can't even go above 2133 at all with 64 gigs? 

I'm going to assume they're the same kit and not mix and matched. 

Well update the bios and try with one stick at a time and check. 

[Acme]

Yeah.  All 4 are Corsair LPX 3000 Mhz C15.

 

Latest BIOS on my mobo.

 

I tried all sticks in pairs, switching them around.  In 32 GB config (2 DIMMs of course), it has no problem running at 3000 Mhz.  In either banks.  I tried all of them, they work.  But when all 4 are in, it fails.  I can't go over 2133. 

 

I don't know man, this is weird.  I definitely broke something when one DIMM was incorrectly inserted but I don't understand what's going on.

[Dr0y]

I don't know much about those things but I'm wondering ... is it possible that it's the memory controller on the cpu that got damaged and not the ram or motherboard ?

[Acme]

9 minutes ago, Dr0y said:

I don't know much about those things but I'm wondering ... is it possible that it's the memory controller on the cpu that got damaged and not the ram or motherboard ?

That's a possibility and I thought about it but I don't know enough about the IMC.   Could be something that is activated when all two banks are full, and for some reason it fails with any overclock what so ever, but run all fine at stock RAM speed (that part for me is weird, I would think if it works, it should work even when OCed). I don't have another CPU to try so I can't confirm.

[Acme]

I just ordered a 9900K so I'll see.  I was planning an "upgrade" anyways and the recent price drop on this CPU and the fact it's a drop-in for my current system is nice.  I'll use the 8700K for my dad's PC, he'll need an upgrade for Flight Sim 2020 anyways and the plan was use some parts from my PC for his build, and he will never need more than 32 GB of RAM, ever.  If it's the IMC, it'll never be an issue.  If it's not, then I'll see.  I may go for LGA 1200 or wait for Zen 3.

 

[Acme]

So I know I'm feeding my own thread... but the 9900K didn't solve the problem, so it's not the IMC on my 8700K.  Digging further, I went to the BIOS and disabled MCH Full Check.  And then it POSTed @3000 Mhz.  I know for a fact that this RAM used to work at that speed on that mobo, so I'm pretty sure it's fine.  Still, I'm running memtest86 just to make sure... first pass is done, no errors found.  I may let it run overnight just for fun.

 

So, this option obviously performs some tests, but it looks like it fails with all 4 DIMMs in for some reason since the "incident".  What broke?  No idea.