Got a Behringer QX 1204 USB Mixer. I attached a condensor mic to channel 1 and turned the phamtom power on. I attached a headphone to the phone socket. I could hear my voice but any number of permutation or combination, I could not add any effect to my voice. The QX 1204 USB is supposed to have FX effects. Where am i wrong?

SOURCE: Korg pa800 mic input makes funny noise

First turn the unit off then rotate the input level volume control. If it feels loose pull up lightly on it as you do this. Also rotate all your controls that you don't normally use a lot. Chances are the pots are dirty. If that doesn't help you might want to check all the connectors inside the unit if you feel confident enough to go poking around. Other wise I suggest that you find a shop that will fix the problem. If you do go poking around make sure the units unplugged and that you have grounded yourself against static discharges. 

SOURCE: faulty effects behringer djx700

The effects on the PMP powered mixers flash UNTIL you push in on the selector knob. This way you can dial in the next effect number and then push in later to activate when you want it... Could yours possibly be the same technique?

SOURCE: my effects on the behringer djx 700 dj mixer stop working how

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.

SOURCE: I just purchased A behringer PMP4000. It has built

Check the FX to main level to make sure it is not too high. Also check the main FX fader level. Try turning each of these down and see if that corrects the issue. The FX fader should control the volume level of the FX globally (mon sends as well as main outs), and the FX to main should only affect the mains output. Make sure FX to mon1 and FX to mon2 are turned all the way down.
Also check what FX program your using and that the FX IN button is depressed, try starting w/ #10 (small room) and see how that sounds.

Testimonial: "Thanks, I'll give it a try and see how it goes."

SOURCE: When i have my FX

Check the 5 volts to the FX unit, If the voltage is low, the FX processor will keep reseting generating clicks, In a different product, the 5 volt filter cap was degraded and voltage dipped down to 4.5 volts causing resets.