I used to do this sort of thing for a living in industry, but if you don't know what the equipment is meant to be doing, it's hard! I am used to setting up brand new equipment, too. Domestic is a whole different world from what I'm used to.
Yup, I know what you mean. It takes just a small amount of info about how a given system is supposed to hang together, which can reduce diagnosis to little more than guesswork until you get it. Once you get a handle on the theory, all the standard techniques can then come into play and it becomes much simpler.
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