B550 board works with 1xxx CPU, but not with 3xxx or 5xxx

Hunex · June 17

Hey Guys,

I bought an used MSI B550 gaming plus motherboard from someone, but when I got it and tried booting, the CPU debug led was constantly on.

Other HW:

R5 5600
2x8GB 3600Mhz Cl17 Kingston RAM (it is in the QVL)
Seasonic PSU

Here's what I tested, to no avail:

RAM in all possible configurations (1stick in all slots, other stick in all slots, etc.)
BIOS flashback to 3 different BIOS versions, including the latest (the process finished, flashing for about 6 minutes then it stopped and powercycled)
Different PSU
Brand new R5 3600, which is supported even with the release BIOS
The same components worked in a different board

I no longer have the board, he bought it back, but he refuses to pay shipping and debugging costs so I'm out of ~25$.
He sent me video of it working for him, but only with a Ryzen 1200 and one stick of RAM from a pitch black room, so he's definitely hiding something.
There was cosmetic damage on the board, so it's totally possible there is other, non-visible damage.

I can't wrap my head around how the board could be working with a CPU that isn't even supported officially (1200), but not with one that is supported (3600, 5600).
Do Ryzen 3xxx CPUs use more pins than 1xxx CPUs? I checked the pinout of AM4 and there are a few reserved pins.

OddOod · June 17

Welcome to the forums!
You're 1000% sure the BIOS you installed was compatible with 3/5k series? And that it correctly flashed?

Hunex · June 17

1 hour ago, OddOod said:

Welcome to the forums!
You're 1000% sure the BIOS you installed was compatible with 3/5k series? And that it correctly flashed?

Yes, the flashback finished without errors.

But it shouldn't matter, as all BIOS versions are compatible with 3xxx series on this board.

However 1xxx CPUs are not officially supported.

7C56v10 is the first available BIOS for the board

OddOod · June 17

Weird... I am seeing reports that some B550 boards did support 1000 series, but very unofficially
After the BIOS flash, did you go into the BIOS and look at the reported version? It's possible on a failed flash it just reverts to the original version. But again, that should allow a 3000 series to work.
Honestly, you got most of your money back, I'd move on. Not worth the energy to be upset about it. Keep it in your pocket as a story about a niche technical problem you've encountered

Hunex · June 17

2 minutes ago, OddOod said:

Weird... I am seeing reports that some B550 boards did support 1000 series, but very unofficially
After the BIOS flash, did you go into the BIOS and look at the reported version? It's possible on a failed flash it just reverts to the original version. But again, that should allow a 3000 series to work.
Honestly, you got most of your money back, I'd move on. Not worth the energy to be upset about it. Keep it in your pocket as a story about a niche technical problem you've encountered

Couldn't get to the BIOS because of the CPU error.

Yeah, I already said goodbye to the money. I'm just curious how I got scammed.