Transformers with VA ratings of 40 VA and above usually have an internal fuse built into the secondary windings. This makes it imperative for the service technician not to short across the secondary with a screwdriver (to see if it “sparks”). If the secondary is shorted for any reason, the fuse will open and the transformer will have to be replaced. Regardless of the type of fuse, remember that if you find an open fuse, something must have caused the excessive current. Look for the trouble elsewhere in the circuit.