I've just found the issue.
You're were almost right, the Issue is coming from the Mute signal which was stick to ground.
This mute signal is handled by U36 (74HC595). So, I replace it by another one from the same board and the headphone is now fine.HCHC
I've just purchased a 74HC595 to replace the faulty one and everything will be fine.
Thanks a lot for your support

Please find attached the service manual...

Just found the manual service. This is the headphone schematic:

...

I come back with new updates regarding my headphone issue.
I replaced both of the 10ohms resistors close to the headphone flat cable.
Result : Still no audio.
I confirm the NCP2811 is correctly powered and is fully functionnal.
Indeed, to confirm this part, I noticed INL and INR don't have any signal.
And this is the issue. To confirm this part, I've just taken another audio signal coming from RCA output connector and I've injected it on the INL and then INR pins.
By doing this I confirm that headphone and the NCP2811 are fully functional.
I've found that...

Thanks a lot, I confirm it is the correct datasheet.
OUTL and OUTR are at these locations, and the 10 ohms resistors are also here.
It should be easier to troubleshoot now.
Thanks a lot

I can't find this chip over internet....

After a new verification, Left and Right headphone traces goes to U18.
I've already reflowed U18 chip and all of the parts around it.
With my oscilloscope, when I touch U19 pins, sometimes headphone works again but just for a few seconds and disapear again.
I can see that capacitors are not shorted.
I've found +3,3V, -3,3V and a PWM signal around this chip.
However, I notice that C78 and C79 remains at 0V.
=> Maybe this is the issue.

Otherwise, I've desoldered the 2 resistors which are on the left and right headphone lines.
It is written...

I don't know because I bought it like that.
Everything works fine except the headphone.
I've checked short circuit and open circuit close to the headphone, and from the motherboard.
The thing is, I don't know from which part it comes.
I think I'm going to check if the audio signal is present with an oscilloscope....

Hi,
I recently bought a Numark Party Mix Controller, but I don't have any headphone working.
I've already replaced the headphone connector and the headphone flex cable, but this is still not working.
Do you have any idea about what to check or does someone has the schematic?
Thanks a lot for your help.
Fabien