Hi Calamity,
I seem to have a similar issue, but with a Sapphire Nitro 380x. I use it on a Sega Blast City at 15khz. I use a JPAC from Ultimarc.
With the original bios, the bios boot logo is disorted (as expected) but I can boot up on windows normally at 640x480 and everything works fine afterwards with crt emudriver. All resolutions work.
If I patch the bios with the latest atom 15 version, the bios boot screen displays ok, but then windows goes wild and the image is distorted completely. If I boot with an EaseUS recovery USB, same issue:motherboard logo is ok, but EaseUS boot screen is unusable (flickering, distorted), like if it was out of sync.
As I just upgraded my card from a 7750 (where everything worked: boot screen, EaseUS, Windows, crt emudriver), I also tried to uninstall and reinstalled crt emudriver 2.0 beta 15 16.2.1, just in case. Plugging the 7750 everything is fine (with modded bios). Plugging the 380x with the modded bios, windows is not usable (up to windows loading screen fine, once it shows the user logon, it shows it already distorted).
Would it be possible to take a look and see if the bios patch is anyhow wrong? I'm attaching my original and modded bios.
I tried the other bioses posted in this thread, ati winflash 2.6.7 did not allow me to flash any of them.
If someone has a working modded bios for the Sapphire 380x model I'd also appreciate to share
Thanks a lot for all your time and support, as always!