Scientist are well accustomed to "First Principle" thinking. It's an approach that dates back to Aristotle and holds that before you can solve a problem, you must distill exactly what is known to be absolutely true. By focusing on only known facts, it is much easier to postulate a solution which is based upon a solid foundation of fact. That foundation allows you to speculate on causal factors but such leaps are always based upon core principles.
Sound familiar? Well, if you are a Field Service Engineer (a good one), then this is the motus operandi with which you approach everyday troubleshooting. The trick here is to ask lots of questions before you even lay your hands on a failed instrument. Many times, a user or researcher may get frustrated by such probing, so it is important to explain up front, why you are asking. Just as a doctor cannot prescribe a treatment for a sick patient without reviewing their medical history, an FSE cannot hope to repair a failed instrument without first knowing it's recent history. Both should operate under the "first, do no harm" methodology.
When was the last time it worked correctly? When did you first notice a failure? Were there any environmental changes in the lab (power, air, floods..etc)? Many times, after such probing, an FSE can find very important facts that will make diagnosis faster and more reliable. A PC or software upgrade, a robot crash, a spill...etc.
So, to all those researchers who need to get a failed instrument back online, just remember...it is in your own best interest to share as much info as you can to assist the FSE. And to you FSE's...ask, ask, ask. First, do no harm. No guessing.