Well, the diagrams you are showing are block diagrams, which are merely simplified modular representations of circuit flow. They are not meant to be literal. When your tech could take a whole modular block and say the problem is "probably" here, then that tells us absolutely nothing. Had he taken an actual circuit diagram (schematic) and made notes along the way indicating what voltages where discovered where, then that might actually have been useful.
Long ago, I asked you to make very specific measurements for us to consider. Instead you are now referring to your technician (who can't fix your boombox) and his very "vague" comment that voltages is OK except that it doesn't work anymore at a certain point. We could have told you that months ago. In fact, the point where it doesn't work anymore is exactly what we are trying to find which is why I asked you to take voltage measurements at very specific points. And I would never accept an answer that "everything is OK." Rather I would want exact measurement at exact points.
Unfortunately, it looks like I myself am unable to help you any further. The information that I would need in order to be able to assist from thousands of miles away requires the actual hands on person to be able to perform very specific (though simple) measurement tests that I feel can be trusted. Maybe someone else can help throw suggestions to you.