Repairing dbx 1066 compressor/gate/limiter

[Kesson]

Hi! Hope you're fine! (:

So a friend gave me this unit which had faulty pushbuttons. Sadly I messed things a little up while doing the job.

Here's the schematic hosted:
https://elektrotanya.com/dbx_1066_sch.pdf/download.html

I managed to repair a vias connecting bottom and top with a bridge. After this sound is back on channel 1.

More saddly I managed to destroy channel 2 by an overload occured while testing (too much volume). Now channel 2 is dead and I'm left with channel 1 who seems to work fine.

As I am novice in repairing such kind of stuff and wanting to lurn as much as possible by the way I try to understand the schematic and make a "reverse engineering the signal path from the input. That I destroyed stuff is sad but if I see it as an opportunity to learn even more I will be very happy!

So I'm looking at that first stage and looking at my documentation I see a substractor opAmp configuration. So what I understand is while this a balanced signal that's the stage where te noise accumulated gets canceled out.
But also, isn't there a banpass filter?

In fact what I wish right now is beeing able to calculate theorical gain and expected output for a 1KHz 1Vp-p input. In order to understand what

I would share lot of pictures of my scope and schematics modification with measure points and my references for the formulas but I'm not sure where I should best host my images. Any suggestions?

Cheers

Any help greatly appreciated!

[CapLeaker]

Re: Repairing dbx 1066 compressor/gate/limiter

Lucky you... only thing you have to do is to compare both channels to each other. Since you overloaded it on the input, feed it some audio and follow it with an oscilloscope to the point where you loose audio.

[budm]

Re: Repairing dbx 1066 compressor/gate/limiter

lucky you... Only thing you have to do is to compare both channels to each other. Since you overloaded it on the input, feed it some audio and follow it with an oscilloscope to the point where you loose audio.

+1.

[CapLeaker]

Re: Repairing dbx 1066 compressor/gate/limiter

on the service manual, page 6, U14a. Compare the input to the output. I bet there is nothing coming out. Compare channel two U14a to channel one U7a. You also can try to compare the DC output voltage of U14a to U7a. If U14a output pin (1) is just giving a solid negative voltage like -15V, its bad.

[Kesson]

Re: Repairing dbx 1066 compressor/gate/limiter

Hey CapLeaker!

Sure I have a channel where sound comes out but I'm not convinced that everything is where it should be, especially with the +4/-10 switch.

For example there is no more sound if I switch to -1 on channel 2. That points me out that I have damaged more things and maybe other which are not so obvious...

By the way, channel 2 never had died (I didnt understand how that could be possible to break in this way...) it was just the thershold of the compressor I turned accidentally all the way down during the panic in this late night

Sorry for that! It's was the try after where I controlled again every setting is the same on both channel.

Lucky me I work in a sound system manufacture for 2 or 3 weeks. I already managed the boss to help me with the understanding of the schematic. I told him I will take the thing with me and he seemed to be pretty ok with that!

Because what I maybe didn't mention clearly is the fact that I would like to understand what should be going on and being able to calculate it and thus refresh my electronic background.

Thank's for your time!

Cheers!