PA and PREA work separately and as normal but low output at normal
signal input and control levels. I don't think I've come across this
situation before. The ground or common to all the "level set" pots on
all the channels is missing presumably. You can only get normal
throughput with the pots set in range 95% to 100% of each of their
tracks, jumping from very low to max in a couple of mm of movement and
all such pots would not have failed at the same time. So inside we go.