As the original 6770M joined the pile of failed graphics cards, I upgraded my iMac 12,2 i7 two years ago with an AMD WX3200 already flashed with Apple firmware by the seller and using Open Core and had zero issues. Last month I built an OCLP Monteray USB on another iMac and added the Polaris option but no display after upgrade unless I boot with the OC-CD the seller of the card gave me and that wakes up the display and everything works. I try to install the proper EFI, but it does not work, and it even appears that after reboot, OCLP does not detect that the EFI partition was supposedly rebuilt. Even if I pull the drive and connect it to my other iMac and attempt to rebuild the EFI, it fails to activate the display. What am I missing? Is there any way to resolve this or just easier to back up and start over?