Yes clicks, pops, thumps are generally evidence of DC. That should be easy enough to detect with a VOM. Sometimes evidence of path saturation. An incorrect DC operating point for some interior circuit could result in premature saturation.In general that should not cause DC issues. Bipolar electrolytic capacitors are typically just two polar caps back to back, so not a game plan for ideal performance, perhaps better than polar caps exposed to a negative DC bias. No bipolar caps do not pass DC, but the fact that you replaced them all suggests rechecking your work.
From a quick glance of the schematic, using TL07x op amps do not provide predictable DC offsets, while modest DC voltages are generally innocuous.
Thank you. It's too tight in there to get in with a VOM with the channel cards plugged in. I'd need to find or build some kind of ribbon extender to test the channel card outside of the chassis.
If you are suspicious of DC are any of the potentiometers scratchy when turned (evidence of DC)?
Just the fader, none of the pots. Also, weirdly enough there is some motorboat oscillation that occurs on one of the digital routing switches when the fader is above 0. Also, all of these problems seem to occur only when the fader is above 0 which makes me suspect something in the fader buffer circuit. I replaced the 4580 with an AD8599 and added decoupling capacitors. It's a SIP8 SMD chip and it was my first time removing one and I lifted two of the pads so I had to reconnect with point to point wires but I already measure resistances and continuity and everything looked OK but I will check again.
I really don't enjoy second guessing other engineer's console designs but one perhaps opportunity for an upgrade is the number of "disk" (ceramic disc?) capacitors in EQ circuits. NPO /COG ceramic caps are as good as film however if they are using common ceramic discs consider mylar (polyester), or better dielectric. Mid band EQ circuits are one place where inferior dielectrics can actually be audible.
Aren't most of the ceramic disks in the opamp feedback loops. Its looks like most of the filter caps are actually mylar film. This is a pretty good sounding board and I bought it cheap with issues to get some experience with working on this type of gear.
JR
