The chief fixed the earphones (7)
I believe the answer is:
headset
'earphones' is the definition.
(I've seen this before)
'the chief fixed' is the wordplay.
'the chief' becomes 'head' ('head' can be a synonym of 'chief').
'fixed' becomes 'set' (both can mean decided or determined).
'head'+'set'='HEADSET'
'the' is the link.
(Other definitions for headset that I've seen before include "Assistance for listener" , "listening device" , "communication aid" , "One covers the ears" , "Audio communication equipment worn by pilots, DJs etc" .)