Paul, you are so funny. But that's the way to find a cold solder joint. Don't trust your eyes. 
Cold Joints
Nope, we're not talking about arthritis, or rolling a blunt in the Seattle snow. We're talking about cold solder joints, that is, a solder joint that does not conduct properly. They are one of the most common reasons your new build doesn't measure right (along with mis-wired terminals).
Sometimes you can see a cold solder joint. It might look dull and crystallized or you might see that a wire hasn't been well covered with solder. But lots of times you can't see a cold joint. Don't trust your eyes. It takes all of a few seconds to reheat (or reflow, or rewet) a solder joint. And in fact when a kit arrives at our lab for repair it's pretty much standard operating procedure for our techs to 1) verify component and wire connections and 2) go through and reflow all the joints in a kit - before removing and replacing any components. Often that's all a build that isn't working right needs. Make sure your soldering iron tip is clean, otherwise you will be holding the tip to the work longer than necessary and possibly leaving more residue to further increase the resistance of the joint.
well said. Thanks, Doc. B.
