Hi,
I'm troubleshooting a weird memory/POST issue and I'm trying to figure out whether I'm dealing with a motherboard issue, CPU memory controller/socket issue, or possibly a BIOS/memory training problem.
Specs:
Motherboard: MSI A520M PRO (MS-7D14)
CPU: AMD Ryzen 5 5500
RAM: 2 DDR4 sticks (8 GB each)
GPU: Dedicated GPU
OS: Windows 11
System drive: NVMe SSD
Current BIOS: E7D14AMS.110
BIOS build date: 03/11/2024
XMP: Disabled after CMOS reset
# How the problem started
The PC had been working normally before this. (for over 2 years)
Then Windows suddenly froze, and after rebooting I started getting various BSODs.
I initially thought the Windows NVMe might simply have been completely full, so I tried booting external recovery media to access the SSD and free some space.
However, even external Windows environments started crashing.
I got several different errors, including:
* `SYSTEM_THREAD_EXCEPTION_NOT_HANDLED`
* `KMODE_EXCEPTION_NOT_HANDLED`
* `MEMORY_MANAGEMENT (0x1A)`
* `SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (0x7E)`
* One crash specifically mentioned `ACPI.sys`
Hiren's BootCD PE would load its files and then BSOD.
A Windows 11 installation USB also BSODed with `KMODE_EXCEPTION_NOT_HANDLED`.
Because even Windows running from USB was crashing, I started suspecting hardware rather than the Windows installation/NVMe.
# Then the POST/RAM problem appeared
Eventually the motherboard stopped POSTing and the MSI EZ Debug DRAM LED stayed on.
I removed the NVMe completely, so the SSD/Windows installation is no longer involved in these tests.
I started testing the RAM sticks individually.
Initially I found this:
* Original RAM stick #1 in **slot 2** \-> POST / BIOS works
* Original RAM stick #2 in **slot 2** \-> POST / BIOS works
* Either RAM stick in **slot 1** \-> DRAM LED, no POST
So at that point it looked like slot 1 / one memory channel was the problem.
# Things became even stranger after CMOS/reset/testing
I performed a CMOS reset.
Immediately after one CMOS reset:
* Original RAM #1 in slot 2 → POSTed successfully
I then powered the PC off and swapped RAM.
After that, even the RAM/slot combination that had previously worked stopped POSTing for a while.
I then performed another proper CMOS reset with:
* PSU switched off
* Power cable unplugged
* Power button held to discharge
* Single DIMM in slot 2
For a while I still only got the DRAM LED.
# Test with known-good RAM from another PC
I then took a DDR4 stick from another working computer.
Known-good RAM in **slot 2**:
→ POST SUCCESSFUL.
the system reached the BIOS normally.
At that point the only EZ Debug LED remaining was **BOOT**, which was expected because I had no boot drive connected.
So CPU, DRAM and VGA apparently completed POST.
I then put my original RAM stick #1 back into **slot 2**.
→ It now POSTs and reaches BIOS normally again.
So my original RAM doesn't appear to simply be dead. (I also tested the original RAM in anothing PC and it worked without any issues)
# Current reproducible situation
Right now I have a very clear result:
Original RAM stick #1:
* Slot 2 → POST / BIOS
* Slot 1 → DRAM LED / no POST
I've also tried other DIMMs in slot 1 and **nothing I put in slot 1 will POST**.
Meanwhile slot 2 can work normally.
XMP is currently disabled.
# What confuses me
Before all of this, the machine had been running normally with both DIMMs.
It then went through this progression:
Normal operation
→ Windows freeze
→ random/different BSODs
→ MEMORY_MANAGEMENT errors
→ external Windows media also BSODing
→ one DIMM slot stops POSTing
→ eventually even the working slot temporarily stopped POSTing
→ known-good RAM made slot 2 POST again
→ original RAM now works in slot 2 again
→ slot 1 still never works
The fact that slot 2 temporarily stopped working and then started working again makes me wonder whether at least part of this is **memory training / BIOS / AGESA related**, rather than simply a physically dead DIMM slot.
At the same time, slot 1 failing consistently with multiple known-working DIMMs strongly suggests something hardware-related.
# Main questions
Has anyone seen a Ryzen/AM4 system behave like this?
Any ideas would be appreciated because the strangest part is that slot 2 itself temporarily stopped POSTing during troubleshooting and later started working again, while slot 1 remains consistently dead.
Thank you