UEFI Firmware update causing POST failures on M01-f100a

[kenryo]

I was recently given this HP desktop w/ AMD 4500G, M01-F1224a, running W11 Pro on some 2018/2019 UEFI/BIOS version.

This desktop was working perfectly with the old UEFI/BIOS for about three months with an PCIE x8 gen 3 Ethernet AIC(Add-in Card) plugged into the PCIe x16 slot alongside a single SATA SSD. This was the case til I made the mistake of updating the UEFI/BIOS firmware.

Issue Behavior: After updating the UEFI/BIOS to the lastest version, F.46 Rev.A, the PCIe x16 slot is now causing boot issues.
- If any AIC that is wired for anything more than PCIe x4 is installed into the primary x16 slot, then PC does not complete POST
- There are no beeps, no flashing power LEDs, no display, it just stays powered on without POSTing
- Only when the Primary PCIe x16 slot is empty or using an x4 AIC  does the PC get past POST and continue to boot Windows 11 Pro

As I'm quite familiar with building PCs, I thought this would be easy to solve.
I've tested multiple configurations:
1. Swapping in multiple original OEM PSUs
2. Replacing RAM with known working sticks from other PCs
3. Swapping in various PCIe add-in cards of varying types like SATA AICs, GPUs, Ethernet AICs, NVME AICs, etc
4. Replacing the 2032 CMOS battery
5. Re-flashing the latest BIOS manually with a USB

However, none of the above solves the issue.

I have two questions
1. Is the PCIe x16 slot electrically x4 or the full x16?
  1. I'd love to have either confirmation of that as I can't confirm it myself with the product spec sheet.
I hope it is actually the full PCIe x16 bandwidth... otherwise the following troubleshooting steps I've taken over the past two days have been for nothing.
2. Is there anyway to request a UEFI firmware that can downgrade the device?
  1. Downloading an older UEFI firmware onto a USB and booting it as per the instructions fail due to invalid signature, best I can tell its because this machine does not allow downgrading to older/lower versioned firmware.

[Bill_To]

Greetings @kenryo 

Welcome to the HP Forum.

Very nice troubleshooting.

I have no idea why a BIOS update would deprecate the PCIe x16 slot.

Examine the PCIe x16 slot carefully to verify the entire slot is pinned out to provide 16 data lanes. I have seen HP wire the primary GPU x16 slot at x8, but I've never seen HP wire this PCIe slot at x4.

Windows EFI System Partition:

I'm pretty sure HP stores the most recent BIOS: .Bin and .Sig files in the Windows EFI system partition. So I am surprised you were not able to flash the BIOS using a bootable HP BIOS recovery flash drive. Doing this should bypass the Windows EFI system partition.

It looks like you'll have to *flash the BIOS using a different method.

Remove .Bin and .Sig Files:

In any event, those files (.Bin and .Sig) must be removed from the EFI system partition or the BIOS will flash to the latest version again when Windows starts.

- Option one would be to edit the EFI system partition to continue using the existing Windows installation.

- Or option two would be to back up data. Then do a clean Windows install to prevent flashing the BIOS to the latest version.

Serial ISP Programmer:

I think you might need to *flash the BIOS using a Serial ISP Programmer . Or have a local PC Tech do this for you.

Regards