Behringer DDX3216 repair (psu problem solved, but now distorted sound)

[dutch_anykey]

Hi all,

I successfully fixed a ddx3216 with the help of this forum. So it's a good place to ask advice.

Recently I got another ddx3216 that was having the "all lights on" problem. This points usually to the PSU.
So That where I started as well. Found out soon that the 17 volt rail was missing, and also the analog 5 volt line that is generated in that part of the PSU as well.
This PSU was already re-capped. So I could exclude bad elco's. Rest of the PSU was working o.k.
Upon measurements the +17 volts just wasn't starting and therefore the -17 and +5 volt was missing too. After some measurements and trail and go I found C47 was bad and the cause that Q3 wasnt starting.
So great, +17 volts was there again. But it was very rippled and +5volt was missing. Around that area elco C70 was getting hot. So great another clue where to look. Turned out that D17 diode was shorted. After that replacement all voltages checked o.k. and stable.

Time to put it back in the mixer...
It started up and all functionality seemed to be there. Time to put a sound source to the inputs and headphones as output. Here the new challenge starts and would like to have some input from you
Seems the inputs are working fine. But on the headphones I'm getting a really distorted sound when I want to put the volume a bit louder.
I suspect it has to be the anaout part. Also when connecting the main ouputs to my other mixer the sound is distorted...

Next steps? I need to find a way to see if the opamps are going bad, or maybe still a current problem from the PSU.
any advice is welcome.

kind regards,
Maurice

[dutch_anykey]

O.k.

I tried another PSU from a 100% working ddx3216, all is working fine. So the problem is in the power supply.
Back to testing the PSU. Maybe measure it with a load attached to the 5 volt side.

br
Maurice

[dutch_anykey]

Hi Guys,

One step further. Isolated the problem on the ANA-OUT part. There seems to be a MUTE signal that is also generated in the powersupply. Via a 4 pin connector it is going to the anaout board.
So the problem is when i try to get some more volume to the heaphones or main outputs, it starts sounding distorted....well I found out it really is distorted because the level of the signal is over the limit. When disconnecting this little connector everything is good !!.
Looking in the schematics I can see that this mute signal is fed to almost every output. the signal is activating a transistor that pulls the signal to ground. So that is the problem. No I have to find out why this happens, but I can't figure out why this MUTE signal is there, and why it is coming from the PSU.
Maybe someone can help me on that. I attached that part of the PSU in a screenshot here. For now I'm going to focus on this part and figure out this MUTE thingy...



br
Maurice

[xycarta]

Have you found the problem? Your faders show this noise level?

[rdonne]

I had the same problem. Q6 is faulty. It's a BC546.

[dutch_anykey]

I haven't logged in since a while, so i missed a few posts.
Good one rdonne ! and thank you.
I'm still operating this unit with the disconnected connector and forgot about it

br
Maurice

[johnradioman]

I Wonder if anyone can advise me. I have a DDX3216 in for repair. It just flashes for a fraction of a second when switched on. I have checked all voltages from the PSU and all are OK. Any ideas?