Wait, I read it again, where are you getting the comm fault and what exactly does it say? The IMC controller doesn’t communicate with the F5 drive.
Do you have a checksum error of some kind on the DDP? (Top LEDs on the swing panel) The most common problem I have when doing the F4 to F5 upgrade on these controllers is the U15 chip on the DDP fails as soon as you change a parameter through the CRT.
