Hello, sorry to hear that you are struggling the issue. 

you can replace a RAID controller module or an expansion module by following these steps: 

please check pg 33 Dell PowerVault MD3860f Storage Arrays Owner's Manual

• Remove the failed RAID controller module or expansion module from the storage array.
• Install the new RAID controller module or expansion module in the storage array.
• Open the RAID controller module and connect the cables.
• Verify that the RAID controller module or expansion module is functioning properly.

Thanks for the information

So we have made the operation this morning

switching disks pools to operational controller 0

have to put the incrimined controller 1 offline

removing the controller 1

waiting 1 minute at least

putting the replacement controller in the rack

place the controller 1 online

controller 1 is seen ok by the MD3860 ( cache is active )

But there still is a message in the Recovery Guru section with the  "Cache Backup Device Failed, Unable to retrieve detailed information"

we put all disks pools  on the replacement controller 1

then reset controller 0

and now all is optimal

@Dell-ErmanO​ 

I think you forget to read the 3 last lines that explain how we remove the message 

we put all disks pools  on the replacement controller 1

then reset controller 0

and now all is optimal