[Al Skierkiewicz]

Marshall,
I repair and troubleshoot systems everyday, sometimes down to the component level. On occasion it even results is a redesign of a system or device. People who know me or have watched me work know I take the following approach even though it may sound odd when you first read it. Listen to the device, it is trying to tell you what is wrong. I know people look at me strange when I say this but it is often true. In the case of our current system, there are LEDs on everything. They tell you a good deal about what is working or not. Take the Crio for example, just the LEDs next to the LAN connector can tell you if there is a connection and if it passing data. The LEDs on the PD tell you what power supplies are up and active and this year, what breakers are tripped or missing. Your transmissions tell you when they are stressed, binding, misaligned. The same goes for motors, servos, wheels and camera.
Case in point, I was called in to analyze a teams robot at Championship a few years back. The team was sure the breakers were tripping when the robot went between forward and reverse, but were not sure why. I had the team put the robot up on blocks so that the wheels were not on the floor and had them demonstrate forward and reverse. The noise that emanated from the frame was unreal. When I told the team they had a mechanical problem, they looked at me like I was crazy. I asked them what they were using to drive the wheels. They had a chain drive to a six wheel system with no provisions for adjusting for chain stretch. As the team went between forward and reverse, the chain would throw a link up into the frame and jamb the drive temporarily. (there was less than 1/4" clearance between the sprockets and the frame) It was so loud, there should have been no doubt as to what the cause was, but no one was listening. They still didn't believe me so I had them look for scratches on the inside of the frame and sure enough there was the evidence.
So your best tools in the box are your eyes and ears. Use them and believe in them.