Bottom speakers not working on vs 1520 burning smell has anyone experience this is it the circuitry thats after blowing and can anyone recommend a place to get parts

Electrical parts were bad, I returned the speakers for replacement under warranty. FYI... I opened the back and noticed an electrical burn smell.

The pop itself isn't necessarily a bad thing, but a burn smell and the fact that it's only outputting a crackle likely means that the built-in amplifier circuitry has been overloaded. This can happen a few ways:
1) Faulty power, either a bad cord or a bad outlet
2) Plugging the output of a power amplifier into this speaker - because it has a built in amplifier, this speaker only wants a non-powered line input
3) If the Thru output is (accidentally) plugged into anything that provides phantom power, that could overload the circuitry.
4) A short due to liquid or moisture contact - these cabinets are most certainly not waterproof
In any case, the amplifier part of the circuitry IS replaceable. If you're not comfortable buying one and replacing it yourself (I'd recommend eBay), take it to any shop that sells similar items. If you're extremely lucky, it was just a fuse that needs to be replaced, but chances are you'll need to replace the whole amp.

There is very little to an inspeaker crossover that could go bad unless it was SEVERELY overdriven. I recommend checking the speaker individually on a wire from a stereo or something powered to verify this. A crossover is nothing more than a capacitor (high cutoff) and an inductor.(low cutoff). The 600 watts rating of the cabinet is an RMS rating, meaning, .707 actual peak value free of distortion. This means that you can only drive it about 71% of that without distorting or damaging it. You said, "very little signal gets to the speaker", which sounds like "very low volume" meaning, magnet stuck, speaker not moving much, meaning warped voice coil. Check that the speaker will move back and forth with your hand freely without interference or scratchy noise. If it doesn't, the voice coil is warped and the speaker needs to be reconed or replaced.

The speaker is blown. Did it smell a little funny when this happened. Sometimes they get a faint burning smell when they blow. Some Peavey amps especially older ones are known for letting DC current slip through to the speaker and blows it immediately. Most of the rest of the amp deals with that pretty well so I'm not quite sure what going on with the standby switch. Probably just a blown bulb.

If you are smelling a burnt smell, then you have probably burnt out the speaker coil. You would need to take both speakers to a local repair centre in your area and have them checked out. They may be able to repair the speaker or may have to replace it.

The send and return jacks are only meant to be used with external units such as reverb, effects etc. These units use a low signal voltage. You have probably dam,aged the internal circuitry. You will have to take the P.A. to a repair center that has experience with Fender products. Your warrantee if it is still in effect will not cover the repair. Soory to give you bad news.

If you got smoke and now it is making wierd sounds then it is fried. DO NOT turn it on until it gets seen by a repairman, unless you think fire is a good thing =)

Not good. If you have electronics experience, you can replace the power amp IC to fix it.
Paul