Time for an update. Desk is running and sounding gorgeous. We're trying to fix all the small things on our list step by step. While calibrating the VCA boards I did frequency response measurements on all channels and they are all very good. If these are the original caps they didn't see much action since 95 or they just hold up very good. I will do this with the center section as well but the important cards look recapped and it's just sounding so good. We got a few replacement VCA (13) cards from CML and they are as good as the originals.
I finally got the monitor section running. T2 on the 24 card was faulty and kept the whole monitor section in mono. And a 5534 on the 22 card had to be replaced to get the quad monitor outs running.
At this point a short detent: I already had a replacement 24 card ready. It came from ebay, seems to be a very early on whith tantal caps. I checked it, put it in and it shorted immediately with some nice fireworks of course. Anyway it provided T2 for the original card.
The main outs we're off about 1,5dB, we switched the 26 cards until LF and RF had the same levels and will look into the other two cards sometime soon. Any ideas how to correct this?
I got myself an early christmas present and ordered a new oscilloscope (Hameg/R&S HMO1002) which should be with me anytime soon. It should help following/measuring signals throughout the circuit. Only two things in the center section not working now: Listen mic and the meters. Meters are out because we accidently cut the cables (going through distribution amps in the producers desk, we removed everything from there for our channel extension early in the process and now focus the consequences
).
And we got ourselfes a better ultrasonic cleaner. The desk did not look really dirty but we had some trouble with wire bridges corroding/shorting through to the traces. Maybe the desk was in some not so dry environment for some time where it collected moisture and dust on the cards. Anyway the ultrasonic bath really helps cleaning it and we are very happy with the results. Cards going through it look like new.
That's it for now. Still looking for channels to bring it up to 48.
Greetings,
Martin