Prepared to come round to fix instrument (6)
I believe the answer is:
spinet
'instrument' is the definition.
(spinet is a historical type of musical instrument)
'prepared to come round to fix' is the wordplay.
'prepared' becomes 'set' (set up or ready).
'to come round' indicates putting letters inside.
'to fix' becomes 'pin' (to pin is to fix in place).
'set' placed around 'pin' is 'SPINET'.
(Other definitions for spinet that I've seen before include "Small 12" , "Early keyboard instrument" , "Step in with old musical instrument" , "Instrument resembling a small harpsichord" , "Instep (anag)" .)