It could be a number of reasons that are not obvious. And may require intimate knowledge of the design to discover. But I have soldered and debugged a lot of equipment over the years and confident in the installations of both digital board replacement attempts. So will move on. After my housing move is complete I do have a place for the M7S in my living room with speakers. It will be used infrequently as primary listening is to be via headphones and the S7. Head cans are going to be a totally new experience!