I have a surround sound JBL Synthesis pre-smp. It is behaving VERY
erratically. Some MODE functions work and some don't at all. It
doesnt seem to make much difference which inputs are used, some of the
modes either give one channel or no channels however high the volume
is put. Hall 1 used to work fairly consistently but now it doesn't
seem to work at all. Similarly the tuner input (I use S VID1 for
this) used to work on JAZZ but now it usually doesnt work much at all.

The right hand lights light up when you accress an input which is
connected but with most modes, no sound comes out and with some modes,
only one channel works (not always the same channel!)

The only mode which consistendly works is MONO ENHANCE (with a kind of
falsified sound which you cant use with television on any talk mode
which is how I have it connected) and suspiciously when you try to
access one of the channels which isnt working on both channels, the
non-working channel occasionally flashes on at full volume,
indicationg a dry joint somewhere. But even this isnt consistent
between symptoms, indicating that the unit isnt absolutely sure where
any dry joint is.

Has anyone worked on one of these please?