SEEMS TO BE A LOT OF CRACKLING WHEN U TAP ON THE BOARD NEAR THE EFFECTS IT STOPS

If you have any cables from the effects inserts section of the board inserted, disconnect them. Check ALL sends levels. Check effects processor for L.E.D. signal. .(Assuming you are using the internal effects.)
Here is an excerpt form the manual:
https://assets.peavey.com/literature/manuals/80301359.pdf

Hi, the crackling noise means it needs a service, was it stored in a shed or garage ? As damp storage is the likely cause.

Send audio from board via the "Aux1 Out" to the input of the effects unit. Now connect the output of the effects unit to "ST1" and control the amount of effects to each channel via each channels "Aux1" control. Adjust the Aux1 controls in the output stage (controls on the right side) for proper levels.

Older boards called this connection "effects send" for the output to the effect, and "effects return" for the effects out back to the board. The better choice was to use "effects send" into the effect but connect the effects output to an unused channel on the board. Using this scenario allowed EQ adjustments to be made before mixing it out to the amps and speakers.

Is the number on the effects display still flashing? Can you select effects or is that section dead now? I've had occasions with my Behringer mixers where a bad ground or otherwise improper power supply seems to cause issues with the effects section but the board seems otherwise functional. It has definitely had me scratching my head a few times and is worth investigating.

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.

Hi there,I have the same problem with my flexwave 120. I opened the amp to measure several capacitors on the small effect circuit board. If one of this capaciters have internal short circuit, wich will effect the others causing effects to fail. I removed them one by one to find possible short circuit. All capacitors were ok. I think the problem is in the processor wich is to diffucult to replace. I think it's easier to replace the effects circuit board. But where do we find this board??

Using a common lead pencil, gently tap on the smaller tubes in the unit, listening for noises and crackling to change and the drive channel changes.

It is normal to get a slight twang when doing this from the microphonics of the tubes, however, the crackling and up and down volume points to a bad tube.

This is a wild educated guess.

I repaired a Behringer guitar amp that had a DSP effects in it (BX1200 I believe).

The effects were on a seperate board and the board had its own 5 volt power supply. The filter capacitor for the 5 volt power on the board was UNDERSIZED and it had degraded causing the 5 volts to drop out of regulation, dipping to 4 volts. This caused the DSP effects to fail.

YOUR device MAY use the same DSP OR design.

Check the 5 volt power with an OSCILLOSCOPE to look for dips below the 5 volt operating point that occur at 120 HZ.

Most likely the fuse for the effects circuit has blown, which happens sometimes on mixers with built in effects.

You'll have to open the mixer as the fuse will be inside the mixer on a circuit board (look around inside where the effects part of the mixer is) replace it with an identically rated working fuse and you should be done.