Z790 Carbon, Cold Boot Never Completes, Always Hangs At Debug Code A2


New member
Dec 10, 2023
Hi there,

Building a new machine with the Z790 Carbon motherboard, 14700k, a Samsung 990 Pro SSD in slot M2_1 (the CPU pci-e Gen4 slot), and while it's mostly working it has this odd issue. Every cold boot, or every hard reboot, it'll only get as far as debug code A2 ("IDE Detect") and hang there. Keyboard lighting is on but keyboard isn't active, NumLock doesn't work, Ctrl+Alt+Del doesn't do anything. I've left it there for 10+ minutes and it never gets any further.

Doing a restart from the back panel of the motherboard, it'll then boot fine.

But, from a cold boot, always this behaviour where the first boot hangs at A2. The SSD is performing correctly and there are no other hard drives or SSDs installed at the current time, just the CPU RAM and GPU.

Anyone else encountered this?
What BIOS version are you on? If you're on v19, downgrade to v18, https://www.msi.com/Motherboard/MPG-Z790-CARBON-WIFI/support

The very latest BIOS on 600/700-series boards (the one with the ME firmware ME_16.1.30.2264 update, which is unrelated) has some reports about bugs, so for now, the second-latest version is the known good one (the one saying " Support 14th Gen / next-gen CPU"). The next version with ME firmware is on the horizon, that will likely be the new good version if the bugs are fixed.

Furthermore, your board uses the problematic ASMedia chipset for two extra SATA ports, that chip is nothing but trouble and should be disabled in the BIOS, see here. Avoid putting any SATA drives on its ports, put them on the chipset-controlled ports instead. When the ASMedia chip is enabled, it can cause problems with high DPC latency, instability, bluescreens, you name it.

Also, it would be good to also list your GPU and PSU model, and even your monitor model (since code A2 usually goes hand in hand with the VGA LED on the EZ Debug LEDs).
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That's an amazing response, thank you!

I did flash BIOS to v19 before installing anything, so I'll try that downgrade immediately.

I'll disable that extra SATA thing too (I'll only need one port here anyway for one extra HDD).

GPU: MSI 4080, Suprim X variant, using its "gaming" bios but otherwise stock
PSU: Seasonic Prime TX-1000 1000W 80 Plus Titanium
Monitor: AOC 24G2SP, via DP, in which I've disabled the DDC/CI power saving thing because that typically messes up desktop window layout after a sleep/awake cycle if left on. I've seen the A2 hang with DDC/CI both on and off, so it's not that.
I've disabled the external SATA controller, hasn't made a difference unfortunately (still, good to know it can cause issues!).

Got the v18 BIOS live now, albeit first attempt failed: tried it via M-flash from BIOS itself, it rebooted then hung at A1 code. Had to Ctrl+Alt+Del from there, it did then boot into the flash utility, has taken the downgrade and I've set all my base level BIOS things again (boot priority, XMP, disabling the SATA controller again just for good measure; nothing fancy).

And! It's made it through three cold boots! Even powering off at the wall, and waiting the few seconds for the monitor to decide "no signal" and go into standby.

Thank you so much!

Edit: can't overstate how big of a second wind fixing this has given me. Now I can smoothly reboot reliably into BIOS and Windows I can more readily try and get this seemingly bad 14700k to *actually* run at 5.5GHz. Thank you again!
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You're very welcome, glad i could help!

If you want, you can also report this issue with the latest BIOS to MSI. By now i'm a bit surprised they haven't pulled that version yet, maybe they need to get more bug reports about it.