Phil:
Generally, the most common fault when the input fuse blows, is
either a shorted rectifier diode (or Bridge) or the switching FET (on
the heat sink) is shorted. Shorts on the output side of the switching
power normally cause the power supply to shut down when it starts
drawing too much current.
I would direct my time to checking the parts on the primary side of
the switching power supply. You might try checking the horizontal
output transistor and some of the larger transistors and diodes in the
secondary side if you cannot find the problem in the primary side.
Hope this helps...
John