Today I had to move a SCOM 2012 R2 Operational Database. I executed this process already for moving a Operational Database to a SQL Always On Cluster. For this move I used the Technet article as a reference. After this move I received from Data Access Service and the Configuration Service a service login error on the database. After double checking the steps made my only conclusion was that SCOM was still connecting to the old server. But what setting was the root cause for the error.
Unfortunately in the article on Technet is not complete. This step is well documented in the Operational Database Move for SQL Always On here.
So after executing this step:
On each management server run regedit from an elevated CMD, then edit HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\System Center\2010\Common\Database.
Change the DatabaseServerName to the new server.
After the change of this setting I restarted the SCOM services and the connection to the new SQL server was made and all logon errors disappeared from the Operations Manager eventviewer log.