chinobino.
Hi ales75, I had a similar experience recently with a Z370 Classified K and POST code 23.
 
You mentioned you were "tighetening my memory timings" when the board failed to POST and I suspect you have corrupted your CMOS and 1st BIOS chip with too tight memory timings.
 
Then when you attempted to boot from 2nd BIOS without completely clearing and power draining CMOS, the 2nd BIOS chip was also corrupted - I believe this is what happened to me.
 
Code 23 refers to "OEM pre-memory initialization codes", which occurs just before "2B Memory initialization. Serial Presence Detect (SPD) data reading".
 
This means the board cannot initialise the IMC to start detecting the RAM DIMMs.
 
I had to RMA the board after going through full troubleshooting with EVGA support and a local PC shop.
 
I have Kingston HyperX RAM (HX424C15FB/8) which was not actually C15 despite its name breakdown;
HX = HyperX
4 = DDR4
24 = 2400 MHz
C15 = CAS latency 15
F = Fury
B = Black Heat Spreader
8 = 8GB per DIMM
 
I bought a Gigabyte Z390 UD to test the CPU, RAM and PSU and discovered the RAM is not C15 and is actually C17 (up to C20) when I looked at the SPD profile in CPU-Z and Thaiphoon burner.
 
I think that the board attempted to boot with too tight RAM timings and corrupted CMOS, which in turn corrupted the BIOS.
 
There is no 2400 MHz Kingston RAM on the QVL (only 2133 and 2666) so it possibly could have been avoided had I checked.
 
After I attempted to boot from the 2nd BIOS chip (resulting in code 23) I later read that the correct procedure if you corrupt your BIOS on a dual BIOS motherboard is to first power down, then clear CMOS, remove power from the motherboard and remove the CMOS battery before you attempt to boot from the 2nd BIOS or the corruption in CMOS can corrupt the 2nd BIOS chip as well.
 
Although I did power down and clear CMOS, I didn't remove the CMOS battery to allow power to fully drain from CMOS before I attempted to boot from the 2nd BIOS chip, which most likely corrupted it.
 
The problem is that the clear CMOS button does not actually clear CMOS completely (at least on the Z370 Classified K), I have noticed that the time/date does not get reset and the saved configuration profiles do not get erased either.
 
Having received my new replacement motherboard from EVGA (thank you guys!) I will now be very careful anytime that the board doesn't POST and ensure I always clear and power drain CMOS completely before trying to boot from the 2nd BIOS chip.

chinobino.
 
 The problem is that the clear CMOS button does not actually clear CMOS completely (at least on the Z370 Classified K), I have noticed that the time/date does not get reset and the saved configuration profiles do not get erased either.

bcavnaugh
Not really, it just needs to be Clean Up. They say toothpaste work great if you have not Copper Cleaner.
Make sure after you clean it up to use 90% Isopropyl Alcohol
What does the CPU Die look Like?

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