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Z690 Maximus Hero + Code 55

Level 7
I have had a fairly stable build for the past 3 months: I will preface this with that I have built many PCs over the years and before I take apart the hardline loop to RMA the mobo, hear me out -

Z690 Maximus Hero + 12900K CPU, custom water cooled loop
RAM: G skill Trident Z5 2x32GB F5-6400J3239G32GX2-TZ5RK (not on QVL, my mistake)
GPU: tuf 4090 non-OC

Lately over the past couple weeks I started getting crashing during MW2 and I was running non-XMP at DDR-6200. I finally lowered the RAM to 5200 and I thought it was stable for a few days. Crashed again and I lowered to 4800mhz. Last night crashed while web browsing and switched to auto setting on RAM speed and got error 55 during post and the system wouldn't boot. Took out 1 stick and so far so good with 1 stick in slot B2 (closeer to the CPU).

I ordered G skill 2x32gb F5-6000J3040G32GX2-TZ5RK to test out if the RAM is truly the cause and in the meantime I'll run memtest. Should I be adjusting the voltages and timings? Those settings have been on auto. This kit is on the QVL but I see many people able to get non-QVL kits to work so I'm not optimistic that will make a difference.

Super Moderator

Unfortunately, it does sound like you're going to have to drain the loop and check the CPU. It sounds as though you might be dropping a DIMM due to improper mounting pressure or pad contact.

You may also want to check the stand-off screws are not overtightened surrounding the CPU and memory array.

Remove the CPU block and CPU and check the CPU pad pins, then remount the CPU and block whilst checking for even mounting pressure.
13900KS / 8000 CAS36 / ROG APEX Z790 / ROG TUF RTX 4090

Level 13
You might check for a Bios update, the Z790 just got one which should help with larger memory configurations.

Right now, on the Z790, I am running the same DDR5 64 GBs of memory your are, at XMP I. That board is or is not supposed to be DDR4 and DDR5 compatible?
Maximus Z790 Hero,
Intel i9-13900k
Intel BE200