Interesting side part of the story, I noticed a main filter cap leg not soldered on the main board - totally missed by the assembly! I’ve seen a lot, that was a first for me. The leg was snipped, but no solder.
@rickysnit Oops! Something like that may well have blown your comments out of the water! Power supply bypass (filter capacitors) are far more important than internal wire; if one was not hooked up right there is no way the amp was sounding right.
To test this the cap would have to be disconnected and the amp played again...