Help pls: i7 8700k Prime95 test core fails without even any OC

justwondering · 30 Oct 2018 at 12:55

Okay, Just removed my overclocked i5 8600k , been running great at 4.8

Same memory (3000mhz) motherboard (gigabyte auros gaming k3) h110i cooler.

My first test was intels own CPU checker, it passed that test
then a quick test on Cinebench
Then onto Prime95 :

I downloaded the latest version of prime95, I have reset my bios to default settings.

When running prime95 with no overclock, temps are fine at around 73 degrees...

When performing the "Small FFTs" test , it will run fine, but after 5 - 10 minutes either core 11 or 12 will fail...

This is with no OC on the cpu.

One thing worth mentioning, the computer at no time has locked up or blue screened on me.

I did read it could be the memory (but runs fine on my i5 8600k) so it was recommended to the test the CPU with XMP profile set to off therefore running the mem at 2133.

I bought the CPU 2nd hand from eBay, based on the warranty check on intels website it is an OEM chip so it cannot be sent back under Intels warranty, I have only had the CPU for a 2 days, so I am still covered by eBay returns, the CPU was listed as "used" used on ebay , clearly states by ebay's terms as working as intended, if an item has a fault it has to be listed as spares or repairs, even if someone adds some kind of term and condition to the description text.

Help please, ideally I would like to have some peace of mind with this CPU but if it is failing with no OC what can I try next ?!?!?!

justwondering · 30 Oct 2018 at 14:12

Quick Update, I have changed the ram, thing seem to be working a lot better, but the odd thing is, that the ram worked fine with my overclocked to 4.8 i5 8600k ?!?!?

I shall do more testing, currently only set to a low overclock of 4.1, but working better than before.

justwondering · 30 Oct 2018 at 17:35

Anyone offer some help I have followed very carefully a few youtube guides detailing my motherboard bios on how to overclock, at 4.6ghz with 1.34 voltage , core 12 will always stop working instantly, at 4.5 it is perfectly stable using the prime95 small test (not blend) if I increase the temps, then it will stay stable but then it starts to thermal throttle the CPU ...... I have tried for hours, have I just got a crappy i7 8700k?

does the fact I cannot go beyond 4.5 suggest that if set with no overclocking, with the chip having a turbo of 4.7 does it suggest there is an issue with the chip , or would normal none overclock setting not cause any issues for the 4.7 turbo?

justwondering · 30 Oct 2018 at 18:10

Well just me on this crazy thread at the moment.....have I found my issue ? I have been using the latest version of prime 95 which has lots of AVX testing, tomshardware suggests turning this off or simply downloading an older version recommend v26.6 , running that as my test and things are looking better...............anyone else suggests that was the best thing to use for testing stabiility?

agnes · 30 Oct 2018 at 19:58

Triple check ram timings and clocks against the default from the manufacturer. It's possible they are off but worked for the more relaxed 8600k.

Have you done a FULL restore to default in bios?

Finners · 30 Oct 2018 at 20:03

Wha motherboard are you using? As for the guide you are reading . Every CPU needs different volts to be stable at a set speed, so yours might just need more .

justwondering · 30 Oct 2018 at 20:07

Hi, Thank you for your replies, Thankfully things have moved on since I started using the older version of prime95 that is not running AVX, my stress testing is now much more reliable, I had it tested and working at 5.00ghz, but I have now dialed it back a bit to 4.8ghz as that will be fine for my needs, volts are set to 1.33 , loadline set to standard, tested with realbench and intel cpu tester and it all seems great now , temps at around 72 - 75 , just playing A.C Odysey , no crashes or blue screen, temps a lot lower than when stress testing...

My motherboard is a Gigabtye z370 K3 motherboard, my biggest mistake was not taking notice and taking off AVX while stress testing in the newer version of prime95 , since downloading v2.66 which has no AVX , things are working just great, the AVX was throwing a big spanner in my testing.

doyll · 30 Oct 2018 at 21:54

What is complete system? I'm assuming it's not sig rig because that has 8600K in it.

When was the last time you cleaned filters, radiator behind fan, etc?

justwondering · 30 Oct 2018 at 22:13

doyll said:
What is complete system? I'm assuming it's not sig rig because that has 8600K in it.

When was the last time you cleaned filters, radiator behind fan, etc?

Hi Yes, its the rig in my sig, I have upgraded the CPU to an I7 8700K.

It is all pretty clean in there to be honest, the main heat issue was coming from stress testing with AVX, which left me pondering for a good few hours today, I knew my i5 was working just fine, I even changed the memory, as I seemed to be getting more failed cores using my 4 x 4gb's , but I now believe this was down to AVX , my 2 x 8gb although worked much better right upto 4.5 Ghz , then cores started to fail using Prime95 with AVX, once I had figured out it is best to test without AVX , things all became much clearer and in fairness, I would have been done and dusted in a couple of hours, rather than going around the houses trying things, but all seems really nice and stable now at 4.8ghz been playing my game now for a few hours and it is working perfectly, no blue screens or odd crashes ...

PS my sig rig has changed a bit , I now have a H110i in the system rather than the H80i, same case , graphics card, MB, different ram , same PSU.