A couple of the active speaker outlet 1/4" socket pins could only resist
0.2N-m of torque appled to a 5mm flat blade screwdriver angled into a
convenient hole in each pin and levering at about 45 degree against the
rear pcb. But of course the pbf solderings looked fine.
But prior to taking that rear apart , hot-air and nylon rod engraver
shaker testing. An area of the preamp showed up to x3 increase in output
level playing low temp ,90 to 100 deg C, hot air over. A "bus strip" of
parallel conductors the length of the preamp pcb showed sensitivity to
severe vibration. So will now have to remove the preamp board and see
what is on the other side of that board. No schematic found.