Take big risk with hi-fi we partly repaired (4,4,4)
I believe the answer is:
play with fire
'take big risk' is the definition.
(to play with fire is to take risks)
'hi-fi we partly repaired' is the wordplay.
'hi-fi' becomes 'hifi' (synonyms).
'repaired' indicates anagramming the letters.
'hifi'+'we'+'partly'='hifiwepartly'
'hifiwepartly' with letters rearranged gives 'PLAY WITH FIRE'.
'with' is the link.
(Other definitions for play with fire that I've seen before include "Take dangerous risks" , "Be open to risk" , "Expose oneself to unnecessary risk" , "Take dangerous risk" , "Engage in something risky" .)