Problems with GL2000 (Allen & Heath)!

[João Victor Salles]

First of all, I apologize for my English, I was born and live in Brazil.
Here we go, I bought a used GL 2000 (Allen & Heath), it came with some damaged channels, I managed to fix most of them, but I have a very annoying problem regarding noise, but what bothers me is when I activate the EQ of the channel strip and it adds a strange noise.
I am using a tone generator to input a 1kHz signal into the console, when I activate the EQ, no matter which channel I am on, I have a noise around those 1kHz.
I am not at home to send the photo I took of the Spectrum Analyzer, but I can confirm that the noise starts at output pin 1 of the OPAMP TL072 in the attached schematic.
This is just one of the problems, I will be very happy if someone can help me, soon I will send the photo of the improvised Analyzer with a PRO-Q3 plugin hahaha.

- Kind regards, João Victor.

 

[João Victor Salles]

Somebody?

 

[NoisyIndividual]

Does the desk have a Slate Oscillator at 1kHz?

 

[Khron]

Olá, como vai? Fico feliz que tenha me notado, você foi a única pessoa até agora a me oferecer algum tipo de ajuda.

While I'm sure the OP, as the rest of us, appreciate the friendly gesture, i believe the official language on this forum is still English...

 

[João Victor Salles]

Does the desk have a Slate Oscillator at 1kHz?

Hello, how are you? I'm glad I noticed, you were the only person so far to offer me any kind of help. Regarding the problem at the beginning of the topic, I managed to solve it, for some reason I decided to place a PCB inside the console. But I have another very annoying problem and I'm almost sure it's not the source, as it's not affecting the AUX channels and the common channels. All my Master channels (Subgroup 1-2 3-4 and LR) are sharing a very loud hum, sounding like a cable when it is poorly connected and failing. Strange because they all have the same problem and the problem only exists in these outlets. (LR and subgroups).

 

[João Victor Salles]

While I'm sure the OP, as the rest of us, appreciate the friendly gesture, i believe the official language on this forum is still English...

I apologize, it was a translation error on the page! Would you suspect OPAMP? I find it a little strange because the problem is the same in all Subgroup and LR outputs. I can leave the schematic here if you want to take a look, sorry again for the language error.

 

[NoisyIndividual]

If I was diagnosing this I would disconnect everything except the output module and see if that hums on its own.
Then start connecting group modules and eventually channels until the problem appears.

Or it may turn out that more and more things connected are producing more and more hum.
But then you would at least have some hard data to go on, which is what you need when troubleshooting.

 

[João Victor Salles]

If I was diagnosing this I would disconnect everything except the output module and see if that hums on its own.
Then start connecting group modules and eventually channels until the problem appears.

Or it may turn out that more and more things connected are producing more and more hum.
But then you would at least have some hard data to go on, which is what you need when troubleshooting.

Ok, follow your advice and I've reached the problem area but I still don't know how to solve it.

I left two photos where the L and R Exit would be.
Output L is cleaner than Output R which has a crazy oscillation around 20hz.

To find out where it starts, I replaced the 47/25 capacitor (C3) and it didn't solve it, the low frequency noise occurs on the Negative terminal, between the positive terminal and Terminal 1 of the OPAMP (IC1) there is no low frequency oscillation.

I removed the AFL resistors (R7 and R8) but the problem remains.

Also remove Capacitor 10/35 (C42) and the problem continues...

I attach the schematic sheet to which I am quoting.

- Thanks