I've had a fair amount of experience with ciruitry and weird ass sensors on arcade games and console alike, but the one thing that's a pain in the ass is when somewhere along the line, there's a complete disconnection in the controller. I bet a lot of people have experienced this at one time or another, when you're using a controller, it freaks out and the machine tells you to 'PLEASE INSERT CONTROLLER, DUR', perhaps on and off, and the player doesn't know what the hell.
I can't very well open up the main cable and go to town with a multimeter, so if anyone knows the most likely places where the circuit is broken, well then, get posting. I'm guessing the connection points to the main controller board are most likely, but I'm really not quite certain if others tend to freak out near the flug or just break in the middle like jerks. (any controller/any system, chances are I have at least one of each first party and otherwise)
I'm going to open up a PS2 controller shortly and post a trip report.
Or if you've got other controller questions/answers, post them here.