First thing to do when troubleshooting power circuit boards is look for bad solder joints - and if you don't find any, resolder EVERY JOINT. Fixed about 80%.
------------------------------ Measuring the voltage drop from where power and ground enter the board to where it appears on component leads sometimes reveals open or poor connections, but it requires a schematic or board tracks that can be traced, and touching a lead can move and temporarily restore an open joint, as with this relay pin. It's more certain than checking resistance because probe contact doesn't affect the reading.
In the early 80's incomplete plating inside through holes occurred, we had a hand-held fisheye microscope to visually inspect them. Wave soldering touched only the bottom of the board and depended on capillary action between the lead and the hole plating to solder the top, which could fail at a hole plating break and leave the component side track disconnected. The fix was top-soldering IF you knew where to check. In addition to all component leads I've had to solder a piece of bus wire into every via. The problem had been mostly solved by the time surface mount came out.
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Previously boards had been thoroughly cleaned in Freon vapor degreasers before wave soldering. Once Freon was banned there was no equally adequate and acceptable substitute for cleaning boards enough for machine soldering. Room temperature Isopropyl alcohol mostly worked, but it couldn't be distilled like Freon in the degreasers because the hot fumes are flammable. Boards had to be handled with cotton gloves and we found that vending machine products were coated with silicone to make them slide easily, which inhibited solder from sticking if transferred from fingers.
Production engineering could be contracted out to a consultant, often an in-house engineer or tech who better understood the product's function and company's abilities and had demonstrated problem-solving talent was given the added task. Richard, this is what you have and are doing.
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consultant who took the desk beside me spent much of his valuable time on the phone negotiating the next job.
It's a somewhat thankless job, when a manager calls in help they are admitting they couldn't fix it themself. A problem may be passed around until someone demonstrates progress on it, that's how I got into digital radio and laser space communications, I was the least unfit for the tasks.
A can-do attitude can be both helpful and risky. Many of the big names/talents in manufacturing had quit their previous jobs after fights. Albert Champion was behind both AC and Champion spark plugs for that reason. Usually the discord is hidden but the media showcases Trump's personnel disputes as if they (and he) were abnormal. I'd be more concerned if his subordinates were all sycophantic yes-men, he tolerates dissenting opinions.
I asked Trump about cooperation before the first election but he hedged his answer, he may have been unsure of it. In New Hampshire most Republican candidates for President but no Democrats since Bill Bradley meet with voters in person and are willing to mingle within the crowd and risk unscripted questions as Trump did. Many politically attentive citizens here attend Town Meetings and follow the rules of order in public discussions, such as staying quiet while a designated person is speaking. I pay attention to who does or doesn't distrust and fear us.