Question Default Vcore setting not stable for i5 8400 with Turbo Boost ?

[chadla]

Hello everyone,

I am having a peculiar problem with a i5 8400 Coffee Lake cpu that I recently acquired from eBay.

Upon installing the CPU the system booted normally, however Windows 10 install would crash within 1 or 2 minutes with either MACHINE_CHECK_EXCEPTION or the system would just freeze. At first I thought this is a motherboard problem, however I was able to reproduce the issue with three different motherboards, three different sets of memory and two power supplies. All the testing has been done on the iGPU and overheating has been ruled out with the CPU hovering in low 50s on full strees. Here's a list of the hardware I have used for testing:

• Gigabyte Aorus B360 Gaming 3 WiFi
• Gigabyte Z370PD3
• AsRock H310M-HDV
• 2x 8GB Mushkin PC4-2666 CL16
• 2x 8GB Kingston HyperX PC4-2133 CL14
• 2x 4GB Patriot Viper PC4-3000 CL16
• 530W Thermaltake Berlin
• 520W Seasonic M12 II

After trying all the combinations above including disabling XMP and manually setting memory, I found out than on all three motherboards turning off the Turbo Boost in the BIOS seems to alleviate the issue and Windows 10 install would go through without a hiccup and the system would be stable, however turning Turbo Boost on again after the install would crash the system, shortly after booting into the OS. Further, I tried fiddling with C-States settings and found that disabling these completely would produce a somewhat stable system, however cpu stress test and memory test in Intel Extreme Tuning Utility will result in a blue screen after couple minutes with CLOCK_WATCHDOG_TIMEOUT. This hinted a stability issue and I thought I might fiddle with Vcore values in the BIOS and see if I can get the CPU to be stable. I am currently testing on the Gigabyte Aorus B360 Gaming 3 WiFi as I need the other boards in other PCs and the AsRock one doesn't have Vcore setting. On my first try I had both Turbo Boost and C-States enabled and with Vcore manually set to 1.2v which resulted in successful windows boot and a usable system but the same watchdog error interrupted stress testing. Trying again with 1.25v Vcore both cpu and memory stress testing via the tuning utility completes successfully and the system behaves normally.

I am actually very puzzled at this behavior and the only explanation that comes to mind is an extremely bad bin of a CPU, however I wanted to hear your opinions on the matter and possibly other suggestions for BIOS settings that I didn't think of. Additionally any tips for further stability testing are more than welcome. I would like to keep using this CPU, since returning it is out of the question, but I want to make sure that I wont be constantly dealing with freezes and bsods.

 

[derwouldd]

Did you manage to figure anything out? I'm having a similar issue. I disable my turbo on i7 9700k and system is stable. No crash. I turn it on, crashes are intermitted.

 

[chadla]

Did you manage to figure anything out? I'm having a similar issue. I disable my turbo on i7 9700k and system is stable. No crash. I turn it on, crashes are intermitted.

I ended up going to 1.3V Vcore since 1.25V was still unstable in some cases and it ran fine for a while, until it died in a very strange way. I was messing with some BIOS settings and at some point lost track of the changes and decided to load optimized defaults. Upon restart with the bios defaults the PC didnt post and the POST troubleshooting leds were stuck on VGA. Tried removing the GPU but same thing was happening when I tried to boot only with iGPU. Tried the CPU with two other boards - same thing. All other components are working fine. So I guess it was either bad or degraded chip after all.