Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

[dicky96]

Hi guys
I have this faulty mixer here. Basically the owner says it worked fine at one gig, then the next one it didn't

When I power on, both the L & R LED Meters go to +4 and stay there. This is without any input and with all sliders Level Set knobs set to zero

Also the LED meter on the 24-bit dual engine DSP goes to red (clip)

I didn't connect an speakers but if I use headphones I can hear what I can best describe as a purring noise on both channels

I found a schematic for the PSU There is a 10 way ribbon cable going from the PA/PSU to the mixer section.

According to the schematic I should have on this cable, from the left hand side:
Ground
Right Audio
Ground
Left Audio
+ 15V (red wire) - reads 14.79V
- 15V - reads 15.25V
Ground
+ 48V - reads 46.6V
+ 5V - reads 4.88V

I tried connecting an audio source to Channel 9/10. I ca nsee the rare some 8 pin chips on each input channel (see pics) these are marked 4580 and I found a datasheet that says this is a dual op-amp

With my scope I can trace the audio signal on each output pin of the op-amp chips, up to the row of chips at the top of the PCB (under where the channel numbers are marked on the silk screen - 1,2,3.....9/10, 11/12

I am getting audio signal as far as here but I don't know where to check after that. I still get the purring noise on the headphones and can't hear the audio signal at all

There is no audio signal on the 10 way connector feeding to the PA.

Any suggestions where to check next, and does anyone have a schematic for the mixer PCB.

Thanks
Rich

[lotas]

Re: Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

Maybe something will help

[petehall347]

Re: Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

- 15V - reads 15.25V are you sure its positive ?
check for dc voltages on the outlet to amp .
also turn down pgm .
also check for anything spilled into it ..drinks often get spilled into mixers

[dicky96]

Re: Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

@petehall
sorry no that is a typo
+15V reads +14.79
-15V reads -15.25

@lotas
Thanks for the PMP3000 rar file - this is the one I already have. From what I can see (unless I am mistaken as I am not so experienced on mixer repair) it contains the schematic for the PSU board, the schematic for the Power Amp, and schematic for a mono input channel.

But it does not have the schematic for the main mixer section and I pretty much proved I have audio as far as the output on the last op-amp on the input channel I tested so I am pretty sure the fault is somewhere in the main mixer/DSP section.

Could you confirm that is what the contained schematic is showing?

Thanks

[lotas]

Re: Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

Well, first you need to check the power supply for ripple on the power supply 5v, 12v, + -15v (check electrolyte capacitors for capacity and esr), check grounding (gnd) between the power supply and the main boards and all connectors, check volume controls and others using multimeter (the resistive layer is erased and stops working) and disconnect the 48v power from the power amplifier.

[CapLeaker]

Re: Behringer Europower PMP3000 Mixer - LED Bar Meter sticks at high level

The 48v is the phantom power for the mic’s. I am not familiar with that model, but is it possible to bypass the DSP or turn the DSP off? To me the problem is either the DSP itself, or right at the input of the DSP from what you are describing.