Intermittant loss of bass throughput. Of course not been able to trace .
induce the problem - other than presumed PbF problem.
Owner never uses the monitor output. Main and monitor PA look the same
components but not mirror/same layouts. Any likely problems swapping the
simple screened leads from each preamp section and swapping the PA speaker
output leads?
Will then at least localise the problem to prea , if the problem recurs