Numark Party Mix Headphone Issue

[nams2590]

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

[CapLeaker]

Sounds like something is open or dead shorted. Did it quit all of the sudden or loss of volume over time?

[nams2590]

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.

[CapLeaker]

Oh boy! That’s not nice to trace with. If you do see a, electrolytic capacitor in series with the audio (DC blocker) check the audio going in on one side and the audio going out of the other side too. If the audio isn’t equal, replace that cap.
A headphone only has 3 wires. A audio left and right and GND. That’s it. You check between GND and the other 2 (left and right audio).
if you go backwards from the jack, I think it goes like this: jack, lowish ohm resistor, a dc blocker cap and audio amp. Find that dc blocker cap and check the audio there. Whatever the problem is, it affects both channels left and right. It could be the IC is dead for one reason or other. It also could be a couple of transistors switching the audio to GND close to the headphone jack. Maybe call Newmark and ask for a service manual. They seem to be all right giving out a service manual.

[madan1]

It shouldn't be that hard.
From what I see, there are two analog audio outputs (rca and headphones) so there must be 2 analog audio amps, which should not be hard to find...

[nams2590]

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 01X on it, which means 10ohms as far as I understood.
But I can't read correct values, even if I try to read these out of the PCB.
So I've just ordered SMD resistors to replace these.
Hopefully, this will solve the issue.

[madan1]

What is the U18 ic?

[nams2590]

I can't find this chip over internet.

[madan1]

I can't find this chip over internet.

How about this https://www.onsemi.com/pdf/datasheet/ncp2811-d.pdf

ps: TBH I expected a more generic classD amplifier IC.. but anyways - go with the standard things - check the power rail, signal enable pin, input analog audio and audio output audio pins

[nams2590]

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