Hi Gary64,
Is the coin mechanism mechanical or electronic?
If it is mechanical then take it out of the jukebox in its carrier so you can work on it on the bench, remove the coin mehanism and clean it.
The best way is to use a damp cloth with a smal amount of washing up liquid on it, dry it off and check that the coin rockers are working correctly and not fouling with the coin, check that they will pass through the plate that holds the magnets etc.
If it is electronic check that there is voltage to the coin mechanism interface and again the coin maechanism is clean.
Regards
Alan
Alan Hood
ami-man
UK