As everybody above says, I would say as well.
The hint of that you heart a serious humming buzz might indicate that the main buffer capacitor (that big black thingie with yellow top and 3 terminals) might have gone south while in action. If it did, it can have drawn so much current that various collateral damage is caused, such as overloaded rectifier diodes.
As far as I know those transformers have no internal fuse; the standard for double fault protection came in force late 70's only (resulting into embedded thermal fuses inside the transformer) . There are only external fuses on the primary site. Which in a case of capacitor failure is unfortunate: a short in the power supply section might fry a secondary winding inside the transformer. As we often say: the components are there to protect the fuse. So the primary fuses can still be fine.
Hence, disconnect the secondary wires and measure if they still have continuity, or dead short.
And of course the same thing for the primary side.
Check if both primary fuses are fine.
Then power up with the secondaries still disconnected, preferably with the variac or DBT as the gents say. Can do without, the fuses will blow on the primary site if there is a short on the secondary site before your home goes dark
Those 2-in-1 main power supply capacitors in those Sony series are prone to failing after 45+ years.
Check carefully for leakage traces.
Have your tech measure the capacitance and ESR
Check the main rectifier diodes: still having a forward voltage drop of 0.5~0.55V, and zero leakage in reverse (diode tester should mention open loop or same value when nothing connected to it) ?
Transformer shipping can do if you really want, but expensive and quite some delays during this holiday season.
