Quietly reverse trouble and win through (7)
I believe the answer is:
prevail
'win through' is the definition.
(I've seen this before)
'quietly reverse trouble' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'reverse' becomes 'rev' (I can't explain this - if you can you should give a lot more credence to this answer).
'trouble' becomes 'ail' (synonyms).
'p'+'rev'+'ail'='PREVAIL'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for prevail that I've seen before include "Be current" , "Be victorious" , "Win through" , "Carry the day" , "Prove more powerful" .)