I only saw one pair of monitors in your pic...when you listened to the ABC outs, was that through that same set of monitors, ie: patching each output, in turn, to the same monitor input? If so, it could be the cabling to the Right monitor, or the monitor itself
if it's powered, or its amp, if passive.
Including PS decoupling, there's exactly six resistors, four capacitors and an IC, after the CRM pot (per channel), so not an awful lot to go wrong/intermittent there. This sounds like a wiring issue in the desk to me.
That could be a couple of things. First thing to know is that all of the CRM outs are un-balanced sources that use "balanced" (2 conductor + shield) wiring. These wires solder to the motherboard, just adjacent to the Molex connectors. Since your desk is
an Elite-II, it probably has the mod wherein the female Molex headers are on ribbon cables that "float" the headers off the motherboard. This is a good thing.
It's worth checking the Molex headers for two things:
-
That the wires are firmly inserted into the "jaws" of the Molex contact (these are IDC (Insulation
Displacement Connector) headers, and they work by manually pushing the wire into a long, deep notch that slices through the insulation and then grips the bare wire. I have seen desks where some of the wiring in the ribbon cables was not pushed
all the way into the notch. A small, flat-blade screwdriver will work to push these in, although this whole inspection may be complicated by the fact that the backs of the headers may have been filled with hot-melt glue.
-
Sometimes, the springs inside the female Molex headers get "lazy" and don't grip the male pin on the module properly. If you look through the translucent end of a female Molex, you should be able to see the spring
contact...it folds up like a praying mantis. On a good connector, the spring should touch the opposite side of the connector when there's no pin inserted. On "lazy" ones, it will stay in the compressed position. If you see this, the header needs to be replaced.
BUT, having said all of that, I suspect that the wiring from the motherboard to the patch-bay/EDAC may be a more likely culprit. At the motherboard, the shield and the "low" side both solder to the 0v ("ground") connections on the board. I have seen a situation
where one or the other of these wires breaks off. If the shield wire were to break off at the motherboard, it could make that line susceptible to noise. This is really hard to look for because, while the solder connections are on the top of the motherboard,
the actual wires feed through from the bottom of the board, and that's where the break will be.
Another place to look is the patch-bay. On an Elite-II, the patch bay rows have a circuit board that is populated with the smaller, 0.100" headers, which can have similar issue to the larger headers (0.156") at the motherboard. You could try patching over
the CRM patch points (CRM Out R -> Mon-A R) and see if the noise goes away...if so that points to dirty "normals" in the PB jacks.
~Ike Zimbel~
Wireless frequency coordination specialist.
Manufacturer's Representative
Radio Active Designs (Canada)
FCC:WRBX645