Sound system not working for show (5)
I believe the answer is:
panto
'for show' is the definition.
(pantomime)
'sound system not working' is the wordplay.
'sound system' becomes 'pa' (public address system).
'working' indicates an anagram.
'not' anagrammed gives 'nto'.
'pa'+'nto'='PANTO'
(Other definitions for panto that I've seen before include "lowbrow entertainment" , "Traditional seasonal entertainment (abbr)" , "Slapstick theatre for children (abbr)" , "cross-dressing performance" , "theatrical work" .)