Loudbox Mini fault

[mousecorns]

I have a Fishman Loudbox Mini that has recently started playing up.  The signal output level is much lower than it should be and it produces a lot of 'sh' whenever anything is plugged in (even just a jack plug without a cable attached).

Through reading discussions here and on another forum, I gather that a full schematic is difficult or impossible to come by.  Given my description of the fault, can anyone suggest any possible causes and how I can test it to pinpoint it?  Has anyone else had the same experience with the Loudbox Mini?

Many thanks.

[Enzo]

I don't know the innards of that amp, but it sounds like a bad op amp to me, at least on the surface.

I would verify the 15v rails for the op amps are good, I'd go through the amp and look at the output pins of all the op amps, just to see if anything looks odd.

I'd apply a signal and try to trace it through the amp.

[J M Fahey]

If it has an effects loop or preamp out/pwr amp in jacks, send preamp signal to other amp and feed clean preamp signal from other amp into the Loudbox power amp to at least "split it in 2" and know what section has the problem.