No input signal whole unit lights up but no effects but audition comes through fine

Well, I would say it isn't dropping the level of "the whole pa", it is just dropping the level of the input you have plugged the fx into. Check the settings on your fx unit, there are usually input, output and mix controls that are independant of "the pa" and affect the amplitude of the signal going into your mixer from the fx unit.

If sure that power is reaching and getting into unit, then confirm that a signal is also reaching unit. If both are positive, then your gear is FUBAR if signal is going into correct input.

If it has a effects loop output and input on the p.a. head and a in and out on the reverb effects processor, then yes you can, just run the effects loop output signal into the input on your reverb processor, out of the output back into the input effects loop on the p.a. head, kinda like you would a effects pedal thru the effects loop of a guitar amplifier. hope this helps!

Are you actually sending a signal to the effects unit? normally you would have it in an insert although I know some people who take a sub channel out to the effects unit and then feed it back in through a mix channel if they run out of inserts or aux busses. What you describe above does not make sense to me. Can you elaborate with the full signal path for the effects unit?

You are aware that there are no built in effects, correct? Are you connecting an off board effects unit and having problems with that? You should be connecting the effects send on this mixer to the input of the effects unit - then the output of the effects unit to the effects return on the mixer. With the effects send control on the appropriate channel turned up, you should see signal hitting the effects unit. You'll need to adjust the effects return on the mixer to hear the effects signal included in your mixer output.

First of all it is important that the amplifier must work to produce the output with an input signal. So disconnect and check with an audio test signal on the input line and at the coupling capacitor to the input. If this is fine then the fault is only the connection and it is possible that the input line has shorted and so the input is not acting. But if other inputs are working the connectors must be rewired and soldered once again without any bridging.

Check that: You are using BALANCED interconnection lines (TRS or XLR) everywhere. Low quality cables can cause or let in noise and hiss.

Check that ALL, and I mean ALL interconnected equipment is powered from the SAME receptacle or power conditioner.

Check that you are not using a noisy source or recording system like the internal audio of a PC for instance.

Short the inputs to ground and see if the output noise goes away. Some effects are noisy because the inut signal after effects gets added back into the output.

You haven't described your setup and without that information there is not much more I can add. Ferreting out noise is one of my specialties. In general your input level should NOT be too small as this leads to less signal to noise ratio due to digitizing noise. Look at the Lexicon specs to find what the levels should be. Without the description of your setup I can add no more...

Should be an Aux 1 or 2 output jack on the right side of the mixer. You can come out of the 1 or 2 OUTPUT jack to the input on your processor, and then from the output of the processor to Effects return or to a channel input. By going to a channel input you can then blend the processor's signal with a slider into the sound system with the other channels, while adding tone if needed. By going back into the Effects return, you just blend it overall by adjusting the Effects return knob.
To feed the channels through the processor, turn the AUX 1 or 2 knob up on each individual channel you want to go through the processor. Make sure the AUX 1 (or 2 if you are using that) MASTER knob is turned up on the right side of the console, otherwise nothing will go to the processor. You should see the processors' input light showing signal, if not check your connections. Good luck

It sounds like the guitar level input to the unit is too low.

NOTE: With this product you MUST use an amplified or electric guitar that has a preamp within it.

If you have a straight guitar that does not have an amp in it, buy a preamp to first run the guitar through.

I take it you have made sure that both the cable to the distortion box from the guitar and the cable to the amp are both good. From the description you give, it sounds like there is no signal getting to the pedal. If the cable is good, then the next likely suspect would be the input jack on the fuzz box. Try wiggling it a little with the guitar cable in place to see if it is loose. Some input jacks are unbelievably cheap and flimsy. A crackling sound (static like) is almost always a bad connection. If it was the output jack, I would think that the guitar signal would come through a least a little bit, but you might want to try wiggling that one, too, if the input jack isn't the culprit.

Another possibility to check is the battery, but this doesn't seem as likely. Some effects units devour batteries, especially units that use 9V batteries. I have a multi effect pedal that kills a 9V in about an hour.