Random static and pops

[dmp]

I've had that popping/crackle turn out to be bad transistors. If you narrow it down to the original BC413 / 40360 / 40361 I know of some substitutes that work. I might even have some.
This isn't the blue A range that came from Madison is it? That one also had 990s on the 2 bus

 

[Lawrocker]

Unless your console channel aux modules have been modified, they have no active electronics, just routing buttons. The paddle mute on the channels are after the last buffer on the 2038, so muting every channel will most likely eliminate them as the issue. Is the noise on both sides? If so, that would be a head scratcher. There is a 990 summing amp, then the insert send and fader which returns to another 990 driving an output transformer. If it were in that first buffer, a bad 990 or surrounding component, it would probably be on one side. If it's only pre insert, that probably rules out a leaky supply filter cap on that card. (In my desk they are on the same card). My 2 mix summing/output is the leftmost module in 'the penthouse' of the center section. Sometimes it's as simple as a reseat because ground or B+ is struggling fo current through a bad connection. Every A-range is different and has been bastardized by random techs multiple times over the years. I have lots of drawings at the shop.

 

[pucho812]

I've had that popping/crackle turn out to be bad transistors. If you narrow it down to the original BC413 / 40360 / 40361 I know of some substitutes that work. I might even have some.
This isn't the blue A range that came from Madison is it? That one also had 990s on the 2 bus

Nope it’s not that one but I know the guys who sold it to butch vig. Iirc the console is now in Washington state. Ours is the first mod that, that console followed with the 990’s

 

[pucho812]

Unless your console channel aux modules have been modified, they have no active electronics, just routing buttons. The paddle mute on the channels are after the last buffer on the 2038, so muting every channel will most likely eliminate them as the issue. Is the noise on both sides? If so, that would be a head scratcher. There is a 990 summing amp, then the insert send and fader which returns to another 990 driving an output transformer. If it were in that first buffer, a bad 990 or surrounding component, it would probably be on one side. If it's only pre insert, that probably rules out a leaky supply filter cap on that card. (In my desk they are on the same card). My 2 mix summing/output is the leftmost module in 'the penthouse' of the center section. Sometimes it's as simple as a reseat because ground or B+ is struggling fo current through a bad connection. Every A-range is different and has been bastardized by random techs multiple times over the years. I have lots of drawings at the shop.

Yes they have.
I have it resolved. Which is good. Reseated a few 990opamps, reflowed a joint or two and gone.
Old desks are like old stairs, they creak when you use them sometimes.

I would be curious to see any schematics that reference the 990 sections if you have them. We don’t have that here but I did find some hand drawn notes that I am slowly going over.