Behringer DDM4000 Issue and Repair Ideas

[marklinton]

I recently got a used behringer DDM 4000 DJ performance mixer and while testing I found that the channel 1 inputs (both phono and line) seem to only allow left signal to get through.

There is a small amount of signal in the right channel, but I'm not sure if it's bleeding through.

Is this something that I should be attempting to repair myself? What might a likely component that failed be? Capacitor? I'm pretty good with the multimeter and soldering iron.

Thanks agin.

 

[MAAC0]

That seems a Pioneer DJM copy.
The Pioneer is all digital inside except for the ADCs or DACs.
A DSP handles all inside.
It could be as simple as a bad solder or flat cable / connector.
Open it and take a look.
Get the service manual and check the input op-amps for that channel, if there is signal after them. You can also switch faders to rule them out.

 

[conanski]

Ribbon cables are always high on the list for problems like this.

 

[marklinton]

Thanks for the ideas, a little more testing and it appears that the gain knob on channel 1 only applies gain to the right side (not left as I thought before). When the gain knob is completely off the signal is identical (really low) on both L and R. When the gain knob is increased only the right side signal is amplified.

I took the unit apart (Behringer and their hot glue ) and examined the circuits and also got a copy of the service wiring manual (Behringer DDM4000 Mixer, Service Manual, Repair Schematics)

I don't know what I'm looking for from the diagram or how else to troubleshoot - any tips you guys have would be appreciated.

Cheers.

 

[MAAC0]

The inputs seem to be analog in with 4580 op-amp.
You have to follow the signal. Check for signals on SW2, C10 and AINL+1 & -1.
No signal on C10 ? check IC6 and its corresponding resistors or the pot itself. Then move on to next stage...

Got signal ? follow the ribbon to the other connector ... and so on....

Compare with C6 AINR+1 & -1 (Right channel)

Leave You source connected to this broken channel. Open another working channel fader and connect a wire with say a 10k and a 10uF / 50V capacitor in series to its input and then start following the signal ... or use another disposable amp. This protects the input from VCA DC control voltages. IC7 is a quad op-amp which handles both channels.

 

[marklinton]

So I'm not sure I follow, can you comment on my logic. Looking at the block diagram (which I'm not going to pretend I understand in detail) it looks like the signal on the 1st input (both left and right) go through the same switch SW2 (which I know works because half the signal is there.

It also looks like the same opamp (4580) IC6 is shared between the channels. and it is working because half the signal is being amplified. And also that the pot (VR3) is working because I can adjust the one side of the signal.


Thanks.

The inputs seem to be analog in with 4580 op-amp.
You have to follow the signal. Check for signals on SW2, C10 and AINL+1 & -1.
No signal on C10 ? check IC6 and its corresponding resistors or the pot itself. Then move on to next stage...

Got signal ? follow the ribbon to the other connector ... and so on....

Compare with C6 AINR+1 & -1 (Right channel)

Leave You source connected to this broken channel. Open another working channel fader and connect a wire with say a 10k and a 10uF / 50V capacitor in series to its input and then start following the signal ... or use another disposable amp. This protects the input from VCA DC control voltages. IC7 is a quad op-amp which handles both channels.

 

[MAAC0]

the signal on the 1st input (both left and right) go through the same switch SW2 which I know works because half the signal is there.

Both RCA's connected & one channel only on the switch ?? You found the fault !! Follow the signal from the switch to the RCA input. Probably a broken solder on input PCB.

pot (VR3) is working because I can adjust the one side of the signal.

One of the wipers could be defective.

 

[marklinton]

Both RCA's connected & one channel only on the switch ?? You found the fault !! Follow the signal from the switch to the RCA input. Probably a broken solder on input PCB.


One of the wipers could be defective.

Actually it's a bit different. With signal on the bad channel the gain has no effect. So there is signal being passed all the way through to the outputs, but the gain knob has no effect.

However the same gain knob (it's a stereo input) DOES increase the level of the working channel on input one, so I'm guessing that the problem is within what ever component is responsible for amplifying the signal. I just don't know how to narrow it down.

On the schematic it looks like IC6 and IC7 are the same components for both L and R but with different pins, and there are some capacitors and resistors.

I only have a multimeter and an audio signal that I can use to test with, so some tips would be great.

Thanks

 

[MAAC0]

On the schematic it looks like IC6 and IC7 are the same components for both L and R

IC6 is a dual 4580 op-amp IC7 is aTL074 quad op-amp. IC6 is a gain stage & the second, TL074 is balancing the signal (note the second IC7 stage is inverted, pin 6 & 9 is inverting input. Gain is 1 4k7/4k7)

So there is signal being passed all the way through to the outputs

Is Your gain always at max compared with the other channel ?

Power off !!

Start by reflowing the pot connections. Just touch the pins with the soldering iron and make sure the space between the pins and rest of PCB are clean of solder / contamination. Use a brush & contact cleaner / alcohol to clean the PCB after.

Measure at R75 (in parallel with the pot). Do the same with R24.

Pot on left side ~ 680K in parallel with 50k and rest of circuit, pot on right side must read 0 or near 0 because as You move the wiper to the right (R76 & R25) You short the pot. 0 in parallel with Infinite is 0. Check also R76 & R25. They are in the feedback path (pin 7 to 6 & 1 to 2) with the pot. Gain is adjusted varying the feedback between 470 & 470+(pot in parallel with 680K). Check also for a short in C59 & C34

Pot working ? move on.

Now power on.

Bridge c10 with c6. (This feeds the same signal to the next stage IC7)
Sound on both outputs / VUs dancing balanced ? Means IC6 or nearby components are faulty.

Hope You have cleaned SW2 already and ruled out the path from the RCA's to SW2.