Time Machine Log files

Where are the Time Machine log files stored under Mavericks 10.9?

It used to be that a failed backup would write to /var/log/system.log
Now I only find info on successful backups, not on the failed ones.

Time Machine will run if I start it manually, but not on its own, every hour as it used to do.

Launch the Console.app from the applications/utilities folder.
In the left hand pane select " all messages " ( at the top ) and you can then filer for event type
com.apple.backupd
( Filtering can be done at the top right hand side in the box that says " string matching " )
All messages related to Time Machine should be there.....

Cheers ... McBie