Measure like this:
https://pinside.com/pinball/forum/topic/addams-family-fuse-blowing#post-2654023

..but also check traces to J104/J105.

With power 'ON' there should be 50Vac on J102 between pins (5+6) and (8+9)

Perfect, that's makes me think that the 50Vac from transformer doesn't reach J102.

with multimeter set to 'Vac' , machine 'ON' and J102 plugged in:
-one probe on J105-1
-other probe on J105-2 ( probe can be swapped as this is Vac)

Can you inspect in the cabinet (below playfield) the Black-Yellow wires from transformer and the connector that connects the harness from transformer to backbox. Maybe a wire loose or burnt connector.

Different ways to check.
Without power, you can measure resistance through the windings of transformer.
With power, you can put the probes of multimeter directly into the 10-pin connector of transformer and measure Voltage.

Be very careful because high voltages are here as well. When in doubt, don't work on the transformer.

Those connectors are known for poor connections. Push the wire deeper inside the connector might help.
Seems like J102 (male and female) must be inspected.