AMEK Mozart VCA Cards

Hi group! :sam:
I´m servicing an AMEK Mozart, have succesfully brought six stereo channels back to life.
Now I have a problem with an MZ 11 mono channel.
It seems that there has been a revision of this module, the desk I´m working on contains older and newer MZ 11 channels. The newer MZ 11 channels have a different VCA card, which does not have relays as the VCA cards from the older channels had.
Now the problem: I have one of the newer channels with one of the old VCA cards, and this channel has 20 dB less output. If I try a newer VCA card on this channel, everything works perfectly.
I would like to "bridge" this old VCA card (automation not needed), so that it will be out of the signal path, but unfortunately I don´t have schematics for the new channel and new VCA card, only for the older ones.
Has anyone been there before, bridging VCA cards in an AMEK Mozart, and could help me out?
Other experiences and "tips and tricks" are welcome, too!
Thanks; Toff

You may find that R218 (22R) and R193 (10K) are missing.

[R193 is next to U19 and R218 is between the 2 middle edge connectors].

Re-fitting them should make it work with the old VCA card as normal.

Thank you very very much! :sam: I will try that tomorrow, when we start servicing that desk again.

Slenderchap (or anyone else of course), do you have any knowledge about a way to get rid of all those VCA cards? Many of the old VCA cards have a burned area, where a transistor or resistor got too hot, and destroyed some traces. This has been repaired before, but with "flying leads" and "creative routing", and still sometimes makes trouble. Another Problem with two VCA-cards (from two stereo channels) is, that occasionally (very seldom) and without a reason their relays start switching for a short moment - unfortunately you can hear this in the mix (not cool when a client sits near you). Of course I could try to fix all that, and have to some extent, but for the future the owner of the desk would prefer a solution where all VCA cards would be replaced with simple "jumpered-connectors". Judging from the few schematics I have, it should be possible to make jumpers/connectors I could stick on the connectors where the VCA cards sit. But which pins for which modules to bridge?
Thank you for your help! :sam:

EDIT: I have to edit a passage about some prices for pots, there has been a mistake on my part. The prices which I had been talking about were for special parts. Sorry.
Toff

Hi
The simplest solution is to link out the transistors so that the relays are permanently on or off (I can't remember off the top of my head). Pull the transistor out or short it!
A factory NON automated desk had a different board to replace the VCA card which simply had a 10dB amplifier for fader gain make up.
Burned transistors for the relays was a standard feature which was addressed by the cmos switching of the later cards. Switching the automation supply off forces the VCA cards into bypass but I can't remember if the relays still needed to have automation or desk supply on them, you will have to look at the schematic yourself.

Matt Syson

Good news: I´ve found a way (with the help of slenderchap, who confirmed what I had already thought of - thank you!!) to get rid of those (older=with relays=hot) VCA cards, I can pull them and just have to make three connections (bridges) at the back of connector J5, and it works perfectly. The owner of the desk does not need the automation, so it´s the best solution - all of the (old) VCA cards indeed get very hot because of a transistor and its assorted resistors which simply dissipate (too) much heat. The desk will run cooler without all those cards, and I hope that will lessen some problems with electrolytic caps - I had to replace some of them which are in the signalpath, perhaps they dried out because of the heat (?).

The problem with a "newer" MZ11 channel which unfortunately has the wrong, "older" VCA card (see my first post), is still not solved. If someone finds this thread in the future: The suggested solution for this problem, posted above by slenderchap, is not the right one, there is nothing missing that could be refitted, at least for the situation I have: I have a MZ11 channel with PCB revision "E" (which should have the VCA card MZ 71*) that has the older VCA card GL745 fitted. This channel/card combination has approx. 20dB less gain than it should have. If I fit this channel with the correct "new" VCA card, everything is within specs. If I bridge the "old" card using the method described above, or if I try another "old" VCA card on this newer channel, there is no improvement. This leads to the conclusion, that neither the channel, nor the "old"card is defective: I think the newer VCA card must have extra gain, which the older ones did not have? This could be what Matt describes: If the desk he is talking about had newer MZ11 channels, and needed 10dB amplifiers when driven without VCA cards, that might be the gain I am missing...
We have to get schematics for the "new" MZ11 channel and card, perhaps I can find a solution if I get them (and best would be a solution to get rid of this "new" VCA cards as well, just like the one we have for the older cards). Unfortunately we only have the schematics for the older MZ11...
So thanks again for all the help (especially Matt and Slenderchap) - this group rocks :sam:
Toff

Hi Toffifee
If you don't want automation then simply link out or force the relays into bypass. Likewise force the non relay boards into bypass. ALL modules were correct gain in the bypass condition so use the original cards and do the linking as necessary. If you have 'lost' gain somewhere then either caps are faulty in the VCA card or most likely the module.
Taking the transistors out will make no significant difference to the module temperature so don't get excited about that possibility. These desks needed fans, use 12 volt 120mm types run from the 5 volt supply (before the diodes so it is nearer 6 volts).
MZ11 is a mono channel. Only MZ12 and MZ20 have stereo subcards.
I have a stock of the newer mono subcards but you are better off modding the ones you have if you don't want automation. The 'buffer only' cards were designated TK*** but only a handful of mozarts had them. Call Uwe or Burkhard at Mega Audio for schematics and say Hi from me. Whose deski was / is it? Where was it from?
Matt Syson

Hi
Just fallen over the manual. The VCA cards do not normally have gain, certainly not the 710 series or 745 so if you have lost gain anywhere using the original cards then the module has a fault, most likely capacitors. Check level at 1KHz then 20Hz, a channel normally drops about 1.5dB or thereabouts. There were a few gain oddities on very early desks hence the statement about using the original cards as they would be correct. Switching off the automation supply forces bypass, irrespective of what the grouping computer thinks or indicates. The buffering action on a 710 is needed but you could pull the DG413 out and link relevent audio path pins if you wished.
Matt Syson

Matt, thanks again. I´m on the road doing FOH; I will not see that MOZART-desk for one or two weeks. We fixed the most issues (lots of caps, so it seems they really dry out?)
I think the owner of the desk will be interested in some mono-channels (could you send me a PM with a price or a contact?)
Cheers, Toff