Faulty Audio Channel when using EQ on Xone 62

[alessandromrc]

Hi, I've been repairing a Xone 62 mixer completely, the power supply was completely bad and I had to rebuild one from scratch, obviously I made a linear PSU design and already noticed audio quality improvements compared to the original one...

Sadly when repairing one of the channels, I noticed that when I enable the EQ, one of the channels goes pretty quiet (Right/Left) and I wasn't able to trace back the problem, I've been looking with my oscilloscope and my multimeter practically everywhere and still haven't found a reason of why the signal is low on that side, from what I can notice is that the input of the op-amplifier is low when the eq is enabled and so obviously it's output is going to be low.

Is there anyone who had experience repairing this kind of problem on the Xone 62 or has any idea of what I could check?

Attached you can find the documentation and the board I am talking about is the C3630 issue 2 (Input 3-6 Circuit), if any information or even a scope screenshot is needed, don't worry to ask.

PS. The op-amp is the IC3 (checking output 1)

Also this is my first post so if anything is wrong, let me know and I will try to correct myself for the next ones .

[donlisms]

It seems like you could compare all of the interesting points in the signal path to another channel that works.  (There are so many!). Or you already did that - did it help?

[alessandromrc]

Hi donlisms, I've already tried to compare but if I got to be honest most values do change since they aren't precision components, being around 5% and also not sure if the channels are fully working, I cannot compare that easily. Just by poking around I can see differences between them, and I've been also changing components like sliders, cleaning potentiometers and whatever possible to get it to work... It seems like something is shorting to ground from the output of the IC2 (which is also another op-amp) and on the actual output of it the signal is perfectly fine so it must be something in the path... I haven't been able to find anything I could call "culprit", being honest with you, I've started with the mixer completely dead, with broken connectors, partially working wiring and burnt op-amps, so it was really a big disaster... Already having it to just power on took weeks.

[themadhippy]

Have you checked all the pre/post jumpers are set the same ?Also if you've had power supply issues id be tempted to whip out ic 3 and try a replacement

[alessandromrc]

Hi themadhippy, I have checked the jumpers and I can say there's nothing wrong with them when not using the EQ, everything works fine... the ic-3 has already been changed multiple times just to be sure... I think the problem comes from the signal path coming out of IC2 and going to IC3 since both the inverting and non-inverting inputs are always pretty low on that channel.

Any idea?

[alessandromrc]

I've attached some of the testing I've done on the board, green channel is perfectly fine, the problem comes on the path where I've written "LOW". I confirm that I have checked capacitors and resistor values and also cleaned the potentiometer of such filter, so I really have no idea of where my electrons are going :/.