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Hello, your observations so far support a diagnosis of a failed printed circuit board (95% but not 100%)
'You can do a heat stress test on the PCB by heating it to 125F with a hair drier, it that precipitates the problem or seems to have solved the problem, either way, then the PCB has micro cracks.
Note: your earlier discussion was with a computer program designed to route your question to me, I am a live person, age 75 with 56 years in the business
We can go from here as needed