Maximus Z790 Extreme Persistent Qcode 55 "Detect Memory" issue

[Duncan91]

Starting a post for some help with a detect memory issue I can't seem to solve.

Problem: Can't get past POST, persistently get Qcode 28, 54 and then hang on 55. Using latest (0904) Bios while writing this. Have swapped out RAM from my original kit (F5-6000J3040G32GX2-RS5K) to (F5-6800J3446F48GX2-TZ5RK) as I initally thought it was faulty after remounting everything and trying all slots whilst isolating ram sticks. I have checked all pins and PCB tracks (specifically the ones to the right of the CPU around the mounting holes. No RAM slots provide a successful boot whether I use 1 or 2 sticks. I have tried rolling back BIOS and cycled between chips 1 and 2. I have tried safe boot, battery out, 60s CMOS hold reset, loosening CPU cooler mount screws, loosening Backplate screws and gradual tightening again whilst periodically clearing CMOS and booting.

RAM is always checked and checked again for a firm and correct seating.

Setup;
CPU: 13900K
MB: Maximus Z790 Extreme (0904)
RAM: F5-6800J3446F48GX2-TZ5RK
GPU: Strix 4090
PSU: Be Quiet Dark Power Pro 1200
Cooling: CPU block Heatkiller IV with LGA1700 Heavy Backplate and washer mod (0.8mm), Heatkiller V Pro 4090 Strix

I'm running out of ideas. I appreciate the help, thank you.

[Silent_Scone]

That’s a two DIMM kit. Memory kits are binned in the densities in which they are sold, GSKILL never intended for users to combine them. 

if no POST in B channels at Optimised Defaults (No XMP / memory overclocking)

1)Remove the CPU and inspect the socket pins.

2) Reseat the CPU and ensure for even mounting pressure 

3) Ensure the stand off screws (specifically the ones surrounding the memory array) are not over-torqued.

[Richard3125]

I tried what you suggested, but I still get the same error. I don't know if I should ask for a refund and purchase a new one. 

I didn't know each pair of memories are different. How can I tell each pair apart now? 

[Silent_Scone]

Check the serial numbers on the modules.

The memory vendors bin the modules at the frequency, voltage and timings in a single set. If you combine them with another kit those parameters are no longer valid.

However, if the board fails to POST after clearing the CMOS with all four inserted and you’ve reattempted CPU mount, consider removing the board from the chassis and retesting. If no joy, may need to look at RMA

[Richard3125]

I have to dismount the motherboard if I'm going to ask for a refund anyway, so I'll try what you suggest. Thanks for the advice.

Would you still recommend an Asus motherboard?