My rig:
i9-9900K
ROG MAXIMUS XI APEX
G.Skill 32 GB (2x16GB) F4-4000C19D-32GTZ
RAM works perfectly on its XMP profile which is 4000 MHz CL19-19-19-39 CR2 1.35V.
I'd like to squeeze a little more performance out of it. So I used this guide https://github.com/integralfx/MemTestHelper/blob/oc-guide/DDR4%20OC%20Guide.md
I'm not sure what IC's I have but I set next values
|| || |Maximus Tweak Mode|1| |DRAM CAS# Latency|24| |DRAM RAS# to CAS# Delay|28| |DRAM RAS# ACT Time|56| |DRAM Command Rate|2N| |DRAM Voltage|1.45| |CPU VCCIO Voltage|1.35| |CPU System Agent Voltage|1.4|
And then I'm trying to increase frequency to next step which is only 4100 MHz and it stops on postcode AB. Actually I played with different voltages and it never can pass POST.
MemOK! II switch is ON.
Could it be than IMC degraded over time? VCCIO and VCCSA was on auto voltages which is 1.376 and 1.360.
But I also tried to tighten timings on 4000 MHz and even with CL18 it loads to Windows but OCCT memory test fails in 10 minutes.