Well when it comes to repairs, you need to figure out whether you are afraid of breaking more stuff or not.
Regardless of what category you fall into, I would highly recommend locating your local Old school pinball repair guy. ItA good to have this guy available for many reasons such as you do have time, you give up on an issue, you broke more stuff than the original issue, etc. And it’s just good to keep these guys in business for Pinballs sake.
If your afraid to do any repairs (the fear everyone has when they get their first pinball machine), then try and fix small things (bad coils, switches, etc) and eventually you’ll get brave and move on to something more advanced.
If you have no fear, well then it’s an open book on how to solve issues. Make sure you have the schematics and manual, preferably printed. You are going to be narrowing down issues and you’re gonna want to know the path of the issue. Doesn’t hurt to ask here as well.
With that said, your issue might be a single issue hitting multiple items or independent issues. Pick 1 item that is failing and start there
You mentioned the idol lock, what is error is being reported?