dbx 166xl schemo...

[jef111]

If the problem is not in switches etc, you must measure signals as I said. There's no other way....

 

[MFS90]

There's a crackle noises like a bad contact. That's why i try XLR patches before. So most commonly this is some switch on the 2nd channel not opamp, or VCA.
C81 cap is looking suspicious to. I got mine something like 10 uF 16 V on the 1st channel it's like 10 uF 50 V.

When i open one switch, i see how idiotically and unstable they designed. DBX force you to buy parts (switch in this case) for 1/10 of whole device price.

 

[NoisyIndividual]

Its usually very easy to find a dirty switch, you just press it in and out a bit, and then wiggle it around a bit, kind of half press it to try and force it to make some noise.
It is usually pretty obvious whether the noise is following your mechanical movements or not.

I think you would have noticed this by now, so I doubt this is a switch problem.

 

[NoisyIndividual]

I just noticed from Googling, this has a Side Chain Insert socket on the back. This presumably acts like a normal insert and relies on the sockets switching contacts being properly closed when there is nothing inserted in it.
This socket may have dirty contacts, so I would either shove a jack plug into it a few times, or better still, spray it with Kontact 60 to clean those normally closed switch contacts.

 

[MFS90]

i check all switches on 2nd channel even -10\+4 back panel. They all looks nice. I tooth brush them with pure isopropyl alcohol and run sine tone to see more consistent output - problem still there.

 

[NoisyIndividual]

Have you checked the Side Chain Insert socket?

You could bypass/eliminate this as a problem by inserting a TRS plug with tip and ring shorted by wire.


The side chain signal is actually the signal that controls the VCA. This goes through that socket.
If that signal is interrupted by the sockets bad contacts, you will get no compression.
If that sockets contacts are intermittent, you will get intermittent level changes, i.e. noise on your audio.

 

[MFS90]

Shorted TRS plug don't help too.

 

[MFS90]

I even re-solder all potentiometer PCB joints in case there's some crackle or cold solder joint.

 

[NoisyIndividual]

OK, you are at least eliminating possible candidates.

 

[MFS90]

I'v notice when i raise output >0 there are some really bad things going on.

 

[NoisyIndividual]

I think then you would have to scope the signal from beginning to end, and try and see where this problem happens.

 

[MFS90]

I have no probes with jack plug at the end to connect to soundcard.
With my heart decease, i have hand shaking problems - so i will definitely short something on circuit if i measure with ordinary multi-meter so tiny parts like this PCB have. Chip legs are so close.
I'm an electronic rookie but rookie with some experience. I doubt this is something like VCA or opamp. It's really sound like a electro-mechanical issue.

Yesterday i de-solder 2nd channel output pot. Open it up and clean it inside. Clean, flux the legs and cover with nice solder layer, than out back to PCB.
I'm still have unstable output but in zone like 0.7 db not +5.9 randomly like before.

Still unworkable. Crazy disappointed with DBX (switches specially)