SSL 4000 E/G VCA Group Faders Problem

[nycsudio1]

Right now I turned the computer off and am trying to figure out the voltage issue because I do get 5v in the mix faders and don't need the computer on to use them, so I am assuming that since the vca assignment is just via vca thumbwheel and cables, vca group must work with the computer off or the group faders should at least see the 5vdc. I did recall other mixes and the vca's were there as far as I can remember.

The pinout info shows that I am supposed to get + 5vdc on pin 13 and -5v on pin 14 in the 82e20 card, so I am testing in the main board in their respective pins and so far nothing. I do get + and - 18vdc.

[nycsudio1]

So after poking this thing around all day this is what I found:

Card 82E20 had two bad resistors, which was killing + and - 18vdc at the source. I took care of that then realized that one of the TL074 was shorted and still burning resistors. Replaced the TL074, tested and the card passes all voltages and also put out 5vdc. I also found a few other resistors with crazy values, so I replaced those as well.

The VCA trim now works, but another problem started to happen:

If I assign any fader to any group, regardless if the computer is on or off, I get major distortion. I have to leave both faders near zero in order to get a very high level without distortion.

I also noticed that most op amps specially T7 (TLO74) on 82E20 are getting very hot.

I suspect that there may be other components on this card that are not within specs. I will need to trouble shoot that, however the distortion is something that I was aware was happening years ago with the previous owner.

If anyone have any idea where to look for this problem, please let me know as I have some serious sessions coming soon and will need the vca groups working.

Many thanks.

[sintech]

It maybe worth getting a replacement 20 card, elshiftos has one for sale in the Sell-Buy section 

I'd recap and re-chip, and also look for any bad or shorted traces, that maybe distressing the op-amps.

[nycsudio1]

You are right, it's a great idea. I will check in the sell-buy section now.

Meantime, my card is revision 14 with vca trim. If anyone out there has one for sale, please let me know.

Thanks.

[nycsudio1]

Problem solved.

4 Bad resistors, 1 bad TLO74 and one T29 BFR80 on card E20.

Everything works now.

One last question, if I insert an IDC 50 computer bypass in the vca slot, will I be able to use the vca groups without turning the computer on?

Thanks again for all the help.

[marcmozart]

One last question, if I insert an IDC 50 computer bypass in the vca slot, will I be able to use the vca groups without turning the computer on?

Yes, that works.

[nycsudio1]

That's great.

If anyone has one for sale in the U.S. please let me know.

Thanks again.

[waltzingbear]

just make one from parts from mouser or digikey. picture earlier in thread has all the information.

Alan

[horizonsound]

Hey, quick question, which resistors went bad on your board, and where did you get the BFR80s from?

I have the exact same issue. The main 10R fusing resistors on the 18v rails, and a few 10Rs post the BFR39 / 80s cooked. Glowing red hot and I got smoke!!

Anthony.

Problem solved.

4 Bad resistors, 1 bad TLO74 and one T29 BFR80 on card E20.

Everything works now.