Broken base cable chain is typical for this mechanical unit.
Typical with this trouble are defect cables.
I'm agree with scooter, that's not easy to found this kind of errors.
You can visually check the chain, if you remove the cover on axis 1.It helps, when you turn also axis 1 with the brake release Button.
Also a good idea measuring cables on this unit, when turning axis 1.
Maybe, the error occured, when you turn axis one in another position?
Other ideas for fault tracing:
All 6 drive units have a fault at the moment.
What happens, when we unpluged some motor cables? (with bridge on PTC)
Maybe, we found a combination, that only one have a fault ?
Startup fault from axis 4 comes also with disconnected motor cable?
Hmm thats a good point, but if i disconnect the cable lets say on axis 4 and try to arm , then the fault should come only to axis nr 4 ? (Ofcourse if the axis 4 cable is faulty )
Can i disconnect all motor cables and start one by one ? I mean:
1.connect axis 1, try to arm , if no axis 1 drive unit fault ,then connect axis 2 , if no drive unit error on axis 2 then move on with other ones....