What causes a short circuit between coils? How to repair it?

The main reason for the short circuit between coils is improper handling of the bridge wire between each coil and other coils in the group, or improper embedding method of the lapped coil, excessive keystroke during shaping, etc. Double sandbag or glass fiber covered wire is particularly prone to this fault. If the short circuit point is at the end, it can be properly repaired with insulating paper pads.