Fix material before broadcast (6)
I believe the answer is:
repair
'fix' is the definition.
('repair' can be a synonym of 'fix')
'material before broadcast' is the wordplay.
'material' becomes 'rep' (rep is a kind of material**).
'before' means one lot of letters go next to another.
'broadcast' becomes 'air' ('air' can be a synonym of 'broadcast').
'rep'+'air'='REPAIR'
(Other definitions for repair that I've seen before include "service" , "Fix, mend" , "Maintain" , "Patch up" , "Restore to working condition" .)