Leave TV not connected (3,3)
I believe the answer is:
'leave' is the definition.
(set off can mean to depart)
'tv not connected' is the wordplay.
'tv' becomes 'set' (a television set).
'not connected' becomes 'off' (switched off).
(Other definitions for set off that I've seen before include "Leave on a journey or put in motion" , "Begin journey or detonate bomb" , "Display - mount - start journey" , "Depart" , "Begin journey or cause to ignite" .)