Asus H77 LGA1155 mainboard stopped working with Ivy Bridge CPUs

[Roman555]

Bad symptoms when Ivy Bridge CPU (3rd-gen 22nm) is installed:

• Won't boot OS (just blank screen or stucks at asus logo, monitor is turned on) with hangs at debug (post) code A3;
• USB stick with MS-DOS can be loaded via F8 boot menu;
• Other OSes won't load - hangs or goes reboot;
• Postponed for several seconds reaction to Alt-Ctrl-Del, Reset and Power buttons;
• An operating system starts loading but won't finish if it's left only 1 CPU core in BIOS settings;

What I've already done and it hasn't helped:

• Cleared CMOS many times;
• Flashed different versions of BIOS in a CH341 programmer;
• Updated BIOS to new version using BIOS embedded utility EZ Flash. What is interesting that after this ME region wasn't updated;
• Updated ME region to newer versions using ME update utility for DOS fwupdlcl.exe;
• Set another fully working and tested Ivy Bridge CPU.

Hello everyone!

It was a fully working system MB Asus P8H77-M LE and 2-core CPU Pentium G2030 Ivy Bridge. Recently I was trying to install stable FreeBSD-13.2 there but I think it's not the point. I didn't manage it because after some tries (every installation were successful but OS didn't boot - error about missing operation system) the system got unstable. Finally I tried to run already installed Linux or Windows but they didn't boot. USB sticks didn't boot too.
The system hangs with blank screen at debug (post) code A3 that means the system ready to boot OS. But it never happens. Also the system has very long reaction after pressing Alt-Ctrl-Del and Reset button. Reset always goes with full shutdown. After some fiddlings I realized that I could start loading OS via F8 Boot Menu or call OS loading in UEFI BIOS menu. But OS loading hangs or suddenly goes to reboot. Linux has error just after loading start : "smpboot: do_boot_cpu failed(-1) to wakeup CPU#1". Windows 10 suddenly reboots.

It looks like problem with ME of PCH but I haven't managed to solve it flashing/updating BIOS and ME.

With Sandy Bridge CPU (2nd-gen 32nm Celeron G540 and Pentium G840 2-core CPU-s) everything works well. Just CPU was changed (no other changes).

I'm stuck now. Any constructive ideas are appreciated.

[Roman555]

New observation:
With a discrete PCIe graphics card as main graphics the mainboard + Ivy Bridge CPU are getting boot.
I measured VCCGFX in different modes with a discrete gfxs card installed:

1. Main gfxs is discrete independently of CPU model - VCCGFX = 0.02v (always no voltage)
2. Sandy Bridge CPU, main gfxs - iGPU - VCCGFX = 0.47-0.5v (bios menu, desktop) / 1.22v (3D apps)
3. Ivy Bridge CPU, main gfxs - iGPU - VCCGFX = 0.125v (bios menu) / ? (OS won't boot)

[прямо]

Maybe your G2030 iGPU is dead. Did you try a different Ivy Bridge CPU?

[Roman555]

Maybe your G2030 iGPU is dead. Did you try a different Ivy Bridge CPU?

Yes, I did. G1610 is working for sure but the board behaves the same way.
Finally I've found an option in BIOS settings that can mitigate the problem a little bit. It's a GPU voltage adjustment. It allows to set VCCGFX voltage manually. If I set it into 0.8v or 0.9v the mainboard loads OS normally (no freezing).
I guess a PWM controller of CPU VRM is faulty. But haven't replaced it yet

[прямо]

Congrats for finally confirmed your suspicion that low VCCGFX is the culprit.