To me its similar to looking at / using a road map.
Its all about direction , flow and understanding what components actually do then following the path.

Once you have a suspected problem you need to identify which path the problem is on then do some troubleshooting up stream and down stream to verify. Many times it could be a shorted ( grounded ) component on the playfiled or one that bridges other paths and it makes it more confusing to trouble shoot. These are the ones that the "fix" if often easy but finding it takes time.

Other times a component on the board dies and its a very simple ID and fix.

Get the basics, a decent multimeter and understand how to use it and what the settings actually do. Learn what the components in a pinball machine do and how they work. As to the schematics its following a line thru a maze of other lines but once you have an idea of how things work its a lot less intimidating and confusing. If you want to troubleshoot on the component level (learn what the IC ships do and test inputs and outputs ) you are going to the next level and will need a logic probe or scope.

Often times a IC chip is not terrible expensive so replacing it without testing it is easy. Similar to testing bridge rectifiers that are cheap to replace and do not always test correctly 100%. Some people frown on this as a "shotgun" repair in replacing everything when only one item was bad.
Personally when I rebuild power supplies I put everything new in because the parts are cheap and I like to work on boards / solder.

A good temperature controlled soldering iron or station is a MUST if working on boards.
A desoldering gun also makes board work enjoyable.

Self taught here as well and a mechanical guy by profession ( Toolmaker)