Some hints:-I have tried instal Raven Ridge APU on my windows 7 64bit, worked perfectly with Ryzen 5 1500X before. After bios update for RR support and swap Ryzen for RR system failed boot to windows..... I tried all SATA ports because I thought it wont boot because of M2 SSD disk which is connected directly to the CPU, so I made disc clone on sata SSD and connected it to the Sata ports from Promontory bridge. It doesnt help, system hangs a while after bios post when window animations starts. Then it boots again and said "required device is missing" "use installation disk and repair your computer". I tried everything but I was not able to load win7 system with RR. What is so different inside of this APU from Ryzen CPU ? Is there any way to make it work ? I dont really like win10. Could you test it Stilt please ? Maybe you will figure out, what is the problem. Note: with win 10 fresh installation APU is working flawlesly.
- How is SATA set in the BIOS, AHCI or RAID? If you change from one to the other after an install without changing a setting in the registry first, then Windows will often not boot. Double check that your recent BIOS update didn't change SATA Mode (IDE/AHCI/RAID) from however you had it set up without you realizing. That can cause precisely the same hang on boot you describe.
- Board drivers like SATA, USB 3 / XHCI, LAN, audio, Wi-Fi, etc, shouldn't change at all for a simple CPU swap on the same board. But make sure the chipset drivers are the latest version as it might contain something APU related. If W10 chipset drivers are a newer version than W7 (especially around time of APU release), then try installing those onto W7. Reason being this Coffee Lake on Win 7 guide explains that the "W10 only" Intel chipset drivers are actually W7-8 compatible INF files, so it's possible W10 Ryzen chipset drivers on W7 may work the same way).
- If above fails, then create a "slipstreamed" W7 install (with XHCI & NVMe drivers) onto a USB stick / DVD-R, then test how a fresh W7 install works onto the SATA drive.
What I personally would have expected to happen is for the APU's to boot up fine and show the iGPU as a "Standard VGA Adapter" in Device Manager, but with no supported GPU drivers you'd simply not be able to use the APU for gaming (no hardware acceleration, etc) and for it to be stuck with like a VESA compatible "VGA Adapter". That's pretty much what happens with Coffee Lake on W7 (everything works except the iGPU).
Best of luck. I'd be interested in seeing if anyone else can get these to work on W7.