Like many of you, building an emulator cabinet was the first step to buying real arcade cabinets and PCBs. I now have two additional cabinets (a Primal Rage cabinet that I use for JAMMA boards and a Neo-Geo 2-slot). Also, like many of you, I've learned a lot of this stuff as I go and I'm always trying to help out others that are just getting started. One thing that is overlooked by many jumping into this, is the importance of both owning and knowing how to use a multimeter to troubleshoot problems that will arise.
A multimeter is undeniably a tool that you will NEED if you are wanting to own and work on arcade games, pins, or troubleshoot any other electronics projects.
Despite this, there doesn't seem to be any specific info on the site about using one.
I'm thinking it might be good to have a centralized place (updated WIKI entry and maybe a stickied post) to get people started on diagnosing their problems using a multimeter. As with much of this site, I'm thinking that tips on practical applications are best.
Before you jump into working on an arcade game you should already understand basic electronic principles like circuits, voltage (including the difference between AC and DC), and continuity. You will be dealing with a lot of wiring, so you will have to know how to at least crimp on connectors. Eventually you will also have to have a working knowledge of soldering. You will also need to know the difference between wiring things in series versus wiring parts in parallel. If any of these concepts are unfamilliar to you, read up in a basic electronics book before starting.
Anytime you're working with live electricity be very careful. Taking shortcuts, being careless, and jumping in before you know what you're doing can be extremely harmful to both you and your game.