Post VCA dimming of audio on master 4056 G wtr and ultimation

[Artur D'Assumpção]

Well you say in your post that you swapped the input cards, while the S&H circuits are on the output cards so it doesn't make much sense. There are 2 places i suspect the issue might be and which affect specifically that one master input or output and not other channels:

1 - At the input card some bad decoupling/filtering capacitor on the specific master input channel. This is easy to spot if you go into the !TEST menu and change the analog inputs, you should see the digital level reacting similarly. If it is steady then the problem it's not on the input side of things but rather on the output.

2 - At the output card some bad S&H capacitors (or even the opamp) on the specific master output channel. If you tap the S&H circuitry at several points with an oscilloscope you should be able to see exactly where the fault it.

It might be possibility that a bad PCB contact on the input/output cards onto the computer motherboard and that re-seating the cards just fixed it. What I usually do every time I take any card out I always clean the contacts with a bit of deoxit just has a maintenance precaution.

If the problem is still there and is on the input side of things I bet you're having the same problem but on a different fader and you just haven't noticed yet.

Cheers,

Artur 

[seedubs]

The output cards were swapped. Apologies... We tried tapping the individual components of the s/h circuit which is no easy task given we don't have any extender cards for the i/o comp cards (any one know if they made those and if they are attainable?). We were told by one of our tecs that the caps in those circuits very rarely go bad. (Like Never). For now i am continuing to hold the belief that the cards needed swapping or cleaning. We cleaned ours with an eraser. Tec's idea.

[Artur D'Assumpção]

Well a cap can always go bad if they are electrolytic. But it can be from a opamp or a resistor in the circuit messing it up. I have found broken opamps and resistors in the past, but I've found more caps with problems they are just more common (and transistors but these aren't on the S&H circuit).

If you want to try out, do you remember the Master channel which chip it went to the output card correct? Now that you swapped card you should find which channel is now affecting. I would bet that channel now has inherited the problem (if it wasn't just a bad connection/re-seating issue).

 

 

[seedubs]

  I have been reminded by my partner to include in this report the fact that the problem still exists but it now only dims every other day or so. I am not sure this is the same problem but for total transparency, the problem is still there just not at the frequency that it will stop sessions like it was before we swapped the cards.

[xmax]

A good clue is turning off the fader PSU, the computer defaults to a bypass mode
Artur D'Assumpção can help more in that department. Bad caps on the 26 card
will give you mismatched levels on the quad buss but it usually only happens
after power up/down. If you can keep a eye VCA control voltage on quad
comp/fader that will tell you where the problem exists.

As always recapping and solid power fix a lot of problem with these desks!