Usually when a fuse continues to blow it's a bad cable some where along the line or a damaged terminal that the cables plug into. I would start by checking all the cable leads and making sure they aren't dirty, damaged, or corroded. Also air dust all the boards and pay special attention to the terminals. Also, if a head fails electronically sometimes it can cause the same issue. It's not the best way to do things but you can test this by plugging 1 head in at a time and turning the machine on. When the fuse blows, you know which head is causing the issue.