Master imbalance SSL 4000E """>>>SOLVED<<<"""

[oyanliz]

Hi all,

I need a hand with a problem we have with our 24 channel 4000E console. I have read all the threads regarding to this issue but I´m still not able to fix or locate the problem. I get this from PRE VCA and POST VCA:

- PRE VCA: 0db LEFT <-->  0db RIGHT
- POST VCA: 0db LEFT <-->  -2db RIGHT

All the strips and the master section have been recapped few months ago and the console has the computer and automation removed. We bought the console 2 months ago, so we are discovering issues like this while we are Knowing the console.

Does mean 82E26 cards are ok if PRE VCA signal is fully balanced? Is it a problem caused by 82E27 card? How can I locate the problem? Any suggestion?

Thanks in advance.

Best regards.

Oihan

[sintech]

The best way to trouble shoot this is with a pair of patch leads.

Patch from the Pre VCA (summing output) into the Post VCA Input, over patching the Master fader. Then cross patch Left to Right.

If it makes no difference, then the issue is the 25 card.

If it does make a difference and the issue swaps Left to right, then it's the 26 card.

Also, it could be a dirty patch point

[oyanliz]

Thanks for the answer "sintech". I have been testing different options and I am still lost with this.

I have tried several connections, included "sintech" posted connection, I have taken pictures and I would be very gratefull if someone could show the way for fixing this deviation of the master ooutput.

This is what I get:

- PRE VCA out-> (works perfect) 0db left/0db right
- PRE VCA to POST VCA input-> 0db left/-5db right
- PRE VCA to POST VCA input swap-> (still the same issue) 0db left/-5db right
- POST VCA out-> -2db left/0db right
- POST VCA out swap-> 0db left/-2db right

I'm not sure if card 026 and 025, both are the problem or ... When I swap Post VCA outs the imbalance also gets swapped, but swapping Post VCA inputs the imbalance keeps, does not swap, so ...

Maybe the photos could help better understunding ...

[waltzingbear]

the pictures don't really help, because we don't know what you are measuring.

Where is the digital meter hooked up? On the output in all cases? other points? not clear.

for instance: in the pre vca photo there are two patch cords, are they to the meter? or what?

I would suggest you start with the oscillator out and use one patch cord and never change the oscillator level. First feed the Master Return and take the readings of Lf and then Rf (you might as well do all four channels, its time to fix the board). Are they the same? if not, find and repair the problem.

Then feed the post VCA return points keeping the metering on the output. Are the levels still balanced or not? Find and correct any problems.

Continue back toward the buss where it appears all is good as I understand your test setup.

I suspect there is a dropped (broken) leg on a line and someone has tried to adjust the problem out in the past. Making it a little odd to understand.   (remember that dropping a line in a balanced system will lower the level 6db in the theoretical case)

Cheers
Alan

[oyanliz]

Thanks for your answer Alan, you are right, after reading your post I have realized that the info and photos I posted are not enought clear, so...

I will try explaining what I did:

I have used the signal generator of Pro Tools and I have sent the signal throught to one mono channel. I never have changed the output gain of the Signal generator and did not touch the mono channel neither. I used the same patch cords all the time, same brand, same long.

I have two 026 cards instead of four, so I can use only LF and RF.

Regarding to the photos:

- Pre VCA.jpg-> Directly wired from Pre VCA out to 1-2 line inputs of my converter (Works perfect)
- Pre VCA to Post VCA input.jpg-> Wired from Pre VCA out to Post VCA input and from LF/RF to 1-2 line inputs of my converter
- Pre VCA to Post VCA input Swap.jpg-> Wired from Pre VCA out to Post VCA input (but Pre VCA outs exchanged L<->R) and from LF/RF to 1-2 line inputs of my converter
- Post VCA out.jpg-> Directly wired from Post VCA out to 1-2 line inputs of my converter
- Post VCA out Swap.jpg-> Directly wired from Post VCA out (but Pre VCA outs exchanged L<->R) to 1-2 line inputs of my converter

I will try doing the same tests with one bantam cord (instead of two) and I will remove the 025 card and put it back again, just in case.

Thanks once more for answering.

Oihan

[waltzingbear]

use your red and orange patch cords (converter IN) into the Main Out LF/RF jax on the patch bay. I don't see them in the photos in that position, so they must be somewhere else. You need to eliminate the external wiring in the testing by patching in there.

When you bypass the post VCA stage you have a "perfect" 6db drop. Is that still there when you patch the test cords into the points above? If so, is that a adjustment error or a problem (swap cards to investigate). It could be several problems remember, you need to keep the setup simple and short (ie use the patch points Main Out)

again, approach it in a systematic direction, measure from the outputs toward the busses, solve the problems on the way.

Alan

[oyanliz]

Hi Alan, thank you so much for your help!!

Signal coming from Pre VCA is fully balanced, I am using this output for mixing, but I can not use the Buss compressor and master fader neither. I do not understund the signal flow thru the cards. Pre VCA is after 82E026? Post VCA is after 82E027? Card 82E025 is the last output card?

I have removed the 025 card, clean it a bit and put back again, but  no changes in the balance of the signal after master fader.

I will continue mixing with the Pre VCA out and I will make more test this week.

Thanks.

Oihan

[paramountrec]

Try swapping the left front and right front 26 cards and see if the problem follows. If I remember correctly, the post VCA patch points are taken before the signal gets to the 25 card, so I don't think the issue is there.

Did you replace all of the electrolytic caps on the 26 cards? There's a Roderstein (sp?) capacitor that often gets overlooked - it doesn't look like a typical electrolytic.  I've seen these fail and cause the very problem you describe.

[xmax]

^Yes what he said, also C7 weird ceramic cap can cause this. And neither the pre or post vca
sends are balanced so I do not see how it could be missing a leg. If it's fine on the pre vca and
6dB down on the post the problem is on the 26 card or something is causing the compressor
to compress 6 dB all the time (check control voltage to vca).

[oyanliz]

Hi all,

Thank you so much for all the comments.

I´m so sorry because I did not have time for posting before.

I made more testings and I have taken some pictures of my 026 cards. Before I post my problem here, in the forum, a technitian tried to fix the problem and he made a modification in the cards. He told to me that he left the console calibrated, but still it is not balanced and I still do not know what is the problem. For the moment we are mixing with PRE VCA outputs, so the console it is working at least.

The technitian cut a resistor on both 026 cards and soldered a trimmer in the back side of the cards (see pictures), I was not convinced with it but he says he left the LF-RF outputs calibrated so I should touch the trimmer if the outputs are imbalanced again.

I would be very grateful if someone could give me some ideas for fixing the problems (I see the problem is on the 026 cards) by myself.

Thanks to all, once more.

My very best regards.

[walrus]

Those cards need all their electrolytic capacitors replaced. I suspect your problem is caused by C18, it has leaked. All that mess around C18 and C23 needs cleaning off the card too as it can cause corrosion of other components.
[Edit] R23 should not be made variable, it the cards main output buffer resistor.

[waltzingbear]

agree with Walrus, that is a bad repair.

you cannot make headway til you recap that (those) cards. Flaky caps will cause just the type of reality you are experiencing.

Cheers
Alan

[oyanliz]

Thanks for the replies, Alan and "walrus", I am arranging an order of some  capacitors and the two resistors for recapping the cards.

I will write back when it is done.

Best regards!

Oihan

[oyanliz]

Hi all,

Yesterday, I have cleaned the card with isoprophilic, I removed the trimmer, replaced the 10R resistor and replaced the C18 capacitor (by one of 6,8uF 100v).

I still have the imbalance there. PRE VCA works fine, but POST VCA and LF-RF still with imbalance.

Both cards were recapped a few months ago but they had 2 old capacitors, one I have changed and the other big brown one, witch I am planing to replace with a 100uf Panaonic FM 25v + Wima MKP-2 .01 uf 250v (as proposed Jim Williams).

Any other idea??

Thanks in advance

Oihan

[walrus]

Yes, that old brown C9 capacitor should definitely be changed.
My 1987 schematic shows that cap as a 2.2uF non electrolytic of some sort. The one in your card may be a 10uF non-polar cap.
Not sure if 100uF replacement will have a big improvement over the 10uF, but whatever.