Headphone output not in sync with channel output on djm800 mixer

See if another audio source connected to the mixer produces the same results. Try with the same cable and then with another cable. The purpose of this procedure is to determine if it is the cable and/or the laptop. (Sound card problem???) or mixer.
Is it ALL audio or just specific audio from for instance, a music application? Does it cut out using iTunes?
The mixer may have a bad or oxidized input. Try a different input channel? Are you using headphones to listen? It may be the headphone amp? OR, if audio is produced via amped speakers, it may be the mixer output. Does the mixer have metering? Do the meters also cut out? Does the laptop do the same thing if plugging in headphones to the laptop directly (no mixer)?

It depends on what you are trying to connect. The XLR would be a professional type microphone, it does not have phantom so a condenser mic will not work. The other inputs should match your stereo equipment. The output goes to your amp.
The Samson S-Mix is a miniature, rugged 5-channel audio mixer with 4-line inputs and a single XLR microphone input. The line inputs are comprised of two 1/4" phone and stereo RCA phono connections. Each input channel has a rotary volume control and the outputs include stereo RCA phono connectors and 1/4" TRS phone headphone output. The S-Mix is powered with an 18 volt AC adapter.

In order to help you we would need the make and model of the mixer.

Did sound for a southern gospel group, using a yorkville powered mixer. Not familiar with your mixer, but, on the Yorkville I had an unused 1/4" line level output with the monitor mix on it. I bought a cigar-sized, 3-channel headphone amplifier / splitter from Radio Shack, called a Boosteroo. Has 1/8" stereo plug that I adapted to the mono output, with a 1/8" stereo to 1/4" mono adaptor. It receives the line level (monitor in our case) signal and supports up to qty 3 - 1/8" plug headphones. Battery operated. No volume control, so I added an inline dial (rheostat) volume control cable. Can't pull up on Radio Shack, now, but, found it available, elsewhere, online. Worked great for me!
Good Luck SdDude

You must have aux sends on each individual channel and each AUX MASTER turned up for output and each of those outputs must be going to separate amps.

There can be any number of reasons for this problem - solve it diagnostically by starting with something that you know is working and work through systematically to the other end.

1. Test a microphone on a separate amp to make sure it works okay. Check amp and speakers working. Check that all output cables from mixer to amp are working by testing separately.
2. Plug microphone into a channel on mixer. Also plug in headphones and turn headphone volume control up.
3. Make sure input sensitivity knob is turned up a bit (say half way) and main output faders (yellow) are up.
4. Check that channel is turned on (little button just above the channel fader- needs to be pressed down)
5. press pfl (pre-fade listen) button (next to button to switch channel on)- do you get any sound on main output or headphones or any indicator lights on mixer to show signal is getting that far (eitehr the individual channel metering lights or the main ones in the central section)?
6. turn off pfl - make sure channel fader (slider) is up - normal position is ) - about 3/4 of way up. Check lights again on individual channel and main output section - any signs?
7. Is the sub mix button for the channel pressed down - in which case you will need to bring sub mix (red) output faders up as well as main faders.
8. If you have got signs of signal on the individual channel but not main see if the channel has been routed somewhere odd (like a subgroup of channels).
9. Plug a working amp and speakers into one of the auxiliary outputs and use the relevant auxiliary send knob (on each channel just above the faders and pfl switches) to pan some signal to that auxiliary out - do you get anything? There is also a headphone socket for listening to the auxiliary channels (with a selector switch /knob to determine which one - make sure it is in the right position) try listening to the auxiliary output with headphones - anything? If yes the problem lies in the main output section.
10. Check that there is not a jack plug in the insert socket (to route signal through an external effects unit) without a matching return jack being plugged in - if appropriate is relevant effects unit switched on and correctly set up - if unsure remove the insert plug to take it out of the system.
11. Make sure any mute buttons are not switched in on main outputs.

You can download a full user manual here http://www.allen-heath.com/gl/gl2400

This is likely a very simple problem. Look for a connector that you did not seat properly or got pulled off when you opened the unit. The cables are often short and pull off the connections or even break a wire. It is NOT likely you need a new power supply.

ALSO see if you might have pinched a wire when re-assembling the unit.

If the hum is observable in headphones, then it is likely a power supply problem, usually a dried out electrolytic filter capacitor.

Behringer only give the manuals to their authorized service agencies I am told.

Mixers are very symetrical and have lots of diagnostic capability from the outputs.

If you headphones work, chances are the moxer biss es are OK which probably focuses the problem on the output drivers.

Use headphones to see what jacks work... Remember that a stereo headphone will only have sound on one side for the mono jacks you test.

If your mains have a dedicated slider, one half of the slider could be bad. Usually you can tell those by a rougness as you slide them.

my outputs dont have signal