Working on a Miprom21 DDC that has "No BC Feedback" fault

I understand that this is a MSU "BCI" (Balance Complete Input) that originates from the drive "Motion adapter" board

with the ribbon cables it's difficult to meter this signal

I have re seated ribbon cables, boards, changed both "BCX" and "BC" relays with no luck

I'm leaning towards faulty "Motion Adapter" board in drive

Is there something else I should be looking at that this "BCI" input monitors that I can check?

Thanks for any suggestions