I have a Bryant Furnace and I am getting Code 24. 3AMP Fuse is blown. The 120V to 24/40V transformer inside the unit is humming. With a meter I'm getting 20V off a lead, and 28V off another lead. If I disconnect the lead wire from the control board the fuse does not blow. Could this be a bad transformer or am I leading myself in the wrong direction.

The fuse that is blown is on the low voltage side which protects the transformer in the case of a short. Disconnect the low voltage wires, install a new fuse, if it blows again you have a bad circuit board if it doesn't, you have a possible low voltage short.