ch5 and ch6 are down in level. Shared by SMD U500 dual op-amp and DC in
that area ,different to the other channels , so changed it, and the same
lack of throughput and same DC. Must be something else further upstream
loading that area
Will remove a 000 ohm to isolate to confirm first . I did not fully check
ch7,8,9 initially as different structures but I think they were low as well
, so something further upstream , requiring full dismantling as the boards
overlap, c'est la vie