SOURCE: Low volume from Fishman Loudbox
I have seen defective XLR cables so check it with an ohmmeter. It is possible the mic input preamp has been damaged. If that is the case, the unit will have to be repaired.
Fishman iis you best bet http://www.fishman.com
You can download the user manuals, they do have a block diagram, but the scan is pretty bad.
It may end up the person looking at it is going to need to rely upon their general knowledge.
My own suggestion is to pull the chassis out so you can work on it while powering it. And then work your way through the amp with either a signal source plugged in at the input, and with high impedance headphones with test lead ends, go through each audio stage carefully. until the fault is isolated. If it is not caps or the rectifiers in the power supply, faulty ground connections to chassis or faceplate, a faulty 4558 is most probable. The headphone approach is the fastest way to address this last one. If a different series of preamp chip is used, a good source for the IC datasheets in general is Digikey http://www.digikey.com and parts too.
Testimonial: "Thanks for your prompt and concise reply John. Indeed I have the manual however the engineer would like to work with the schematic diagram. I have emailed Fishman and await their response..The only info I can find on the website is the manual... "
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