Hi:
I have the KJ7800-PRO Mixer. If you are not getting any vocal effects, ensure the echo button is pressed down. This button is under the right side of the equalizer, and just under the Cue/live button for the headphones. Right side of mixer, just left of master echo level knob.
After you verify that the echo button is depressed, ensure you are giving any effects on the master controls. Try these settings on the echo, turn the master, the delay, and the repeat knobs all to one click past center. Now make sure the mic you are singing on has it's echo control set to about 1/4 of max level.
I use these settings and get great vocals with my UHF-5800 microphones.
If you have any questions let me know, I know this mixer well.
Felix the KJ