Sorry to hear how this has turned out for you Daniel.
If i'd just sold the guy the machine i'd kinda feel like i should fix it , but then if you made it perfectly clear that it mustn't be turned on without the board in it then he only really has himself to blame.
If it were me i'd feel obliged to fix all the boards for nothing , but charge him for your time traveling and make him pay for the stuffed coils , i'm sure there will be a few of them....i'd be very surprised if there weren't!
