DBX 118 output distortion

[Golgoth]

Hi everyone,

I once again have a faulty DBX 118 I am trying to repair (not the same unit as my 2016 thread).

Initially the unit was not passing audio. I replaced every capacitor except the ceramics and every IC on both the motherboard and the RMS and VCA cards.
Now the unit is passing audio, and the RMS detector seems to be doing it's job and correctly reacting to "above" and "below".

Correct voltage on the PSU +/- 12V C4 capacitor, and on the card connectors pins 7 & 8.

With both knobs at 12:00 the audio sounds "correct". But if I try to set the threshold to either low or high position, and then turn the compress/expand pot, I am getting complete distortion of the signal where all the original signal is replaced by noise. The issue is worse in "above threshold" mode where distortion is maximal at 11:00 or 1:00 already. Takes a little more turn to reach the same level in "linear" mode.

I checked the signal with a scope and a sinewave, result below (both knobs at 12:00 position first, left/right setting with a crazy pic in the second picture).

Any idea what to check next or what could be the distortion's cause?

Does anyone have a working unit we could compare trimmers' voltages for example? I'd also like to check VCAs pin 2 "EC" voltage which is variable. The issue here is I have no idea of what the correct voltages should be at most points in the circuit except for the +/- 12V rails.

Thanks!

 

[abbey road d enfer]

The issue here is I have no idea of what the correct voltages should be at most points in the circuit except for the +/- 12V rails.

That's where you should start, though.
I could give you a hand if you happened to be in the Paris area.

 

[Golgoth]

That's where you should start, though.
I could give you a hand if you happened to be in the Paris area.

Hi Abbey,
That's very kind of you! I am in Paris 3rd district.

 

[abbey road d enfer]

Call me at zero six zero huit zero un vingt nonante

 

[JohnRoberts]

check connections to VCA or that could be faulty. Abbey can help sort it out...

bon chance.

JR

 

[Golgoth]

Call me at zero six zero huit zero un vingt nonante

I'll call you tomorrow if that's fine for you

 

[abbey road d enfer]

Okey doc! Not too early, please, I'm a night owl...

 

[THH]

DBX-119 No Compression
Hello.
--I just bought a used DBX-119. cleaned the connectors, pots & switch and it worked perfectly with Compression set about 1.4, Mode switch set to Above Threshold & Threshold set at 100mv for 3-1/2 movies, then suddenly no sound from either channel.
--I isolated the problem to the 119, cleaned the pots further & re-soldered several connections on the bottom of the board that appeared poor.
--Then reinstalled it, got blasting audio at first bit of Expansion side & seemingly normal as I turned it further clockwise - BUT turning CCW in Compression resulted in weak audio (required the amp be turned up very high) from 1.0 -> 1.1 that dropped off very rapidly to no audio by 1.2 and beyond, except with very slight sound with amp turned up very high.
--Then cleaned and lubricated the pots but same result except the audio did not blast in the first bit of Expansion - just seemed normal.
--Threshold settings from 100mv to 1 seemed to make no difference at all in the sound output.
--I'm not a skilled technician and do not have a deep supply of parts, but I can solder and follow instructions.
--Can anyone give me some guidance?
Thank you very much...Tom