All my hardware was delivered, so I gleefully set about building up the new system to start playing with it... I figured go ahead and put it in the case from the start because surely there'd be no downside to that, right?
Many would build up a new system to a minimal point where it runs, on a desk, in the open, just to test basic functions... I've done this often enough to know it's a good idea, but not recently enough to remember to do it this time.
I bought this Ryzen 5 3600x; (on the right) note where it says "3rd Generation"
The ASUS B450 motherboard I chose was delivered wearing a BIOS version 1002, dated 2019-03-07 ... which won't boot with that cpu. No beep codes, no video, no nothing, the fans turn and the RGB LEDs dance through their colors, but thats it.
This pretty acrylic case I'm using is nice for accessing everything and fiddling with bits with the top off; but there is no spare space at all. Room for the fans and the motherboard and the wires have to be coached around very very carefully.
Of course, I'd put in all the ram and hooked up all the fiddly little case switch stuff (which is a shitshow in this case). Just to maximize the fail.
After reading a little on the net, I came to the opinion that this was probably a BIOS issue. This review of the motherboard (dated 2019-09-24) mentions:
The first thing we should highlight is that opting for the Asus TUF B450M-Plus Gaming and a 3rd Gen Ryzen CPU will mean a lottery when it comes getting a board with a compatible BIOS. Thankfully, if the worst happens and your board doesn't POST and you don't have an older CPU to perform the update, you can use AMD's processor loan scheme whereby it will send you an old model to do that with. It will take time, of course, but you will eventually be up and running.
That and the existence of the mentioned AMD CPU Loan program helped convince me this was a possibility.
However, because of the lack of beeps, I'm also still aware of the possibility of there being deeper problems; after all motherboards are complicated critters and there's a fairly high DOA rate.
Also the ASUS site swears up and down that this motherboard should be OK with this CPU. AMD docs say the motherboard should have worked with BIOS version > 1201; but without another compatible CPU in the house theres no way to see the BIOS version that i could tell.
Therefore, I found a local (-ish, an hour's drive away) "Best Buy" store where they had a Ryzen 3 3200G, and an ASUS TUF X570 motherboard available on the shelf.
That CPU is "2nd Generation" and should work on the B450 board if it works at all. And if it doesn't, I've got the X570 I couldn't convince myself was worth the extra money originally, that should work and prove out the rest of the components.
Sure enough, the Ryzen 3 CPU works on the B450 motherboard immediately, and it shows the outdated BIOS version and confirms the problem.
Updating the BIOS to the current version with that CPU, lets the board run as trouble free with the Ryzen 5 CPU.
I am so happy that wasn't all that much of a big deal.
Now I have a spare motherboard and CPU; and I happened to have bought enough RAM and can break loose other parts that I can pitch this to Rhe as an upgrade for her computer too. (Once we get another case and monitor, to be sure... and probably some other stuff).
The value of having two computers of this generation for cross testing parts and so on is pretty high, and she needs a new system pretty badly herself; so it worked out fortuitously in the end.