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

[seedubs]

There is a issue with our console In that the audio seems to be dimming on both sides randomly. The condition can be heard on the post VCA patch but not the pre VCA patch which would lead us to look at the 27 card which supplies the voltage to the rails on the 26 card (I'm told this by people smarter than I). We looked at the 27 card and replaced some charred resistors on t11 and t12 but to no avail. We are getting by for now by patching the master before it hits the post VCA card and it sounds fine. Any one out there know where we should look next or if indeed we are at least looking in the right direction? Would the I/o cards for the ultimation be a place to look? Thanks in advance for any guidance ?

[seedubs]

Another weird condition associated with this is that it reacts to faders being pushed up or down even if there is no audio coming from the channels. It will be sounding strong and then the second you push a fader it dips in volume. Strange ....

[waltzingbear]

your second post leads me to wonder if there isn't some sort of bad offset in the system. Changing (fading) the DC can cause odd things to happen later in the circuit.

Alan

[seedubs]

Im starting to think it has to do with the fader system There is another condition having to do with the keyboard/cpu freezing that seems to coincide with this fader system problem. We checked all the voltages on the 24 25 26 27 cards and they are all within spec so i doubt it is the card cage. We deleted the master fader object and re created it in the two windows and both problems went away for a couple hours then slowly came back. Its as if there is a grounding that happens and it dims the audio and causes the cpu to lock up for a period until it discharges and things clear up. It was fine for the first month now it is a serious problem for us. Thankfully it only occurs in the post VCA patch, not the pre VCA. Same faders causing havoc but only post VCA. Talk about a full time job!

[waltzingbear]

hang a scope or dmm on the control voltage port for the vca. Since this is a ultimation board that should be the only place that level can be modulated without something actually moving.  Could be either the card or the computer D/A output to the card.

Alan

[seedubs]

I have found that if i turn off the fader psu( not the motor psu) the problem goes away.

[waltzingbear]

thats back to the control voltage. the 5V from that supply is the source for the control voltage sent thru the fader and then to the computer and then back to the VCA.

Dig deeper there.

bad cable on send or return from computer?  (swap to test)
bad voltage coming out of computer (unlikely, but possible)

what does the screen say when you bring up the VCA levels in the computer? do you see the level changes there as well?

[seedubs]

All excellent suggestions. Thanks. Do you mean look in the session set up windows to see if the values are fluctuation in the software on the master VCA?
 Does any one know of a schematic available for a  Ultimation fader psu (Not the motor psu but we'll take those too)? Keep the ideas coming ! Many thanks

[seedubs]

Excuse my ignorance but where would be a good place to begin measuring the control voltage. (0-5V)? Should we take the master fader out?

[seedubs]

I found the schems for the 688 fader psu. Looks like there are +15v -15v and 5v being developed in there. I see lots of caps that might be causing problems. I will start at the psu and work my way to the master fader checking for proper voltages and the all important 5v control voltage for the master fader.

[seedubs]

We checked all of the voltages emanating from the 688 and they are all solid. No sign of bad caps or resistors. Restarting the system seems to help but only for a while. Sometimes it behaves for an hour after restart but always returns to the dimming . Some channels when moved cause the problem worse than others. Channel 14 always causes the dimming when moved while others not at all. It comes and goes but is never usable for mixing. Gonna have better tecs look it over in a few days but even they are not confident they can diagnose or fix the Ultimation so any other sage advise is encouraged. Thanks again!

[billythekid]

I've been following this thread and was curious to see if the other tech had any luck?


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[seedubs]

 I have been meaning to update the forum on our progress with the Ultimation system. After many long days and nights sweating this problem out we were told by one of our tecs to try and swap out the input cards A for B. We did this and it acted the same at first but then calmed down and stopped dimming.  It has been stable for a week now and we are in automation bliss. We traced the problem to the output of the master vca sample and hold which was spitting voltage down the line to the master vca return causing both left and right sides to dim as 0v is wide open and 5v is minimum. I wish we knew what we did in the end to cause the system to change but this one is really a stumper for everyone we flew out to fix it. I for one will not look a gift horse in the mouth but I also will not be surprised if she starts acting up again. It reminded me of the early days with pro tools where I had to keep my mac G3 open in case the comp would freeze and I would have to swap tdm mix cards around to get it to fire up. Maybe the comp needs some shuffling periodically? Either way I am glad to arrive at this point and feel as if we are one of the last of the mohicans with a Ultimation system that actually runs... (Artur excepted) One of the tec's quit SSL over the Ultimation system and is amazed it works at all. He joked.."No one ever says come check out my Ultimation system" Thanks again to everyone who has helped us out with this issue with a big thanks to Artur who is always there to help out with stunning detail. Hopefully this thread is closed! Fingers crossed...

[Artur D'Assumpção]

Ahh! This is good news! I'm glad you finally solved it! Good to know my troubleshooting skills are still sound! In the end the problem was where I suspected, the sample & hold circuitry for the master.  \m/\m/

[seedubs]

  The question then becomes...how did swapping the input cards fix the problem? Did we by swapping the sample and hold circuitry place what was the master fader circuit to another channel possibly not as vital to operations? Is the fault still there just not expressing. We tried to trace the schematics to isolate which channel the master sample & hold circuit might have landed in the swap but it seems pretty murky at these depths . Or , was it the whole "computers from the early 90's need there cards swapped around every so often? Ahh.. the mysteries one opens one self up to in this life...