I require a manual for fender acoustasonic junior dsp 2 channels 40 watt per channel

Those specs would be right - I have this same board but the amp was fried by a previous owner. I pulled the amp board out and tossed it and use the mixer now to drive an external amp. Great board. This amp is rated at 1200W "peak", bridged into an 8ohm load. That would equate to about 900W RMS bridged into 8ohm or 450 per side into 4ohm loads per side. You can't daisy chain all 4 speakers....impedance would be too low. You can run two of your 8ohm speakers per side - that results in a 4ohm load per side for the amp. That would give you amp delivery of 450W per side. Your speakers are rated to handle more than that so you're fine. For the record.....you could run one speaker per side no problem....just lower power output.

This probably an impedance problem. Do you have the manual. If not see if you can get it on line. You can then research the impedance of the input and see if you have a problem. Fender website in support area. Hope that helps. Let me know..

I would try using another speaker to see if you can get the sound back, this will help you narrow down the problem, you can also use the effect send to feed anothe amp to see if you get the sound OK.
It can be blown speaker or output stages,

noise problem with fender jr accoustatics is the poor aluminum sheet ground design that wraps around the body of the amp. it happens to me all the time because i kept on moving/carrying/dropping the amp every time we do church service. i am thinking of using an aluminum cable to wrap around outside the body.

Sch: http://www.schematicx.com/schematic/fender-acoustasonic-junior-jr-guitar-amplifier-schematic/

Turn down the VIP knob and try it. This is on channel 1 for announcement voice overs overriding everything. It has a threshhold setting for adjusting that. Here is the manual for it.
http://support.fender.com/manuals/pro_audio/Passport_P150_manual.pdf

Download it here:

http://support.fender.com/manuals/guitar_amplifiers/Acoustasonic_Junior_DSP.pdf

Well... you probably won't like this, but here is some info: In bridged mode, a different Speakon to speaker cable is required from only the B... it is wired differently and you can only use one of the plugs. The speaker or speaker system CANNOT be less than 8 ohms in bridged mode... this precludes using speakers in parallel or multiple speakers that are less than 16 ohm impedance... such speakers are NOT commonly available as most are either 4 or 8 ohm. There is a slide switch for bridged mode on the face of the mixer. Next thing you won't like... The 1200 Watts specification is PEAK power, NOT RMS... You can get 400 watts RMS per side USING 4 ohm speakers. If you use 8 ohm speakers, each of those will get 200 watts. I use this mixer myself and ALSO repair them. The voltage swing at the outputs is about +/-60 volts MAX (peak). This is about 40 volts RMS by the time the circuit LOSSES are taken into account. Across a 4 ohm speaker you get 10 amps times the 40 volts or 400 watts. Across an 8 ohm you get 5 amps or 200 watts. The voltage rails in the switching amp are +/-70 volts DC so these are reasonable values. Bridged mode just uses both sides of the amp driven in opposite directions for higher voltage out BUT you have to use no less than a single 8 ohm speaker so there is NO advantage to bridged mode power wise. IF YOU NEED more power, use extra speakers from an additonal amp driven by the 1/4 TRS mains output jacks OR use additonal POWERED speakers driven from the same jacks. Please read my tip about the hazard regarding the SLEEVE of the cahnnel A cable when using Speakon to 1/4 plug cables being the HOT and the tip being the cold for channel A. Ground the sleeve accidentally and goodbye channel A amp...

Wrong assumption ! Most likely an electrolytic capacitor blew up. If you open the unit it should be obvious... it MAY also have taken out another component(s) as well. They can make a mess so clean up any residue as it will cause corrosion. Use distilled (non-ionic) water to clean up the residue. The little cans sometimes blow off or spit at the top and spew white crud all over.

Possibly you are holding the switch down???... it MAY activate on the release of the switch. Try quick tap on switch.
I tried to find schematic to analyze this but could not find one.