I've got a piece of equipment that has pretty severe noise on it that I'm trying to improve. It's an older system (built in '96 but a lot of the design is probably late 80's) and is mostly bundles of hook up wire run through it instead of shielded cables with twisted pair wires. It's also largely an analog system, lots of sensors and boards with op amps. Depending on what/where I measure on the system I can get anywhere from ~300mV to ~1.8V of high frequency noise, which seems excessive.
It has a stainless steel enclosure that has DC power supplies, breakers, terminal blocks, some AC distribution. Connected to this is another stainless enclosure that houses a VMEBus computer with various cards that have all the digital/analog inputs/outputs. These enclosures are earth grounded (a 2" copper strap tied to building steel).
It has 2 modular DC power supplies (MeanWell MP650's), one large 24V and one that has 7 outputs (+5, +5, +12, -12, +15, -15, +24). All of the DC- terminals on the power supplies get tied to the enclosure, then most of the DC+ terminals go to breakers then terminal blocks. There's also DC- terminal blocks that are also tied to the enclosure.
The +5V supply that's used to power the VME has pretty severe high frequency noise on it, ~1V pk-pk at ~10MHz. I've got a scope pic attached. From testing that I've done turning various breakers and parts of the system off I think this line is the largest source of noise on the system.
The wiring for this supply is a little weird and I'm not sure what the best course of action would be. On the power supply DC- terminal there's one wire that connects to the enclosure and one that goes to the VME. The power supplies DC+ terminal has one wire that goes to the VME and one that goes to a breaker then a terminal block to go to a couple other devices. Now the VME also has two ground straps between the DC- and the enclosure. With this I've got unequal currents running through the two main lines that power the VME because half of it is returning via the stainless enclosure. These two lines are also bundled with ~20 other wires that go to various places.
I've got a diagram attached showing these connections and roughly how it's laid out in the enclosures. I'm thinking that I should remove the two ground straps on the VME use a twisted cable between it and the power supply. I would like to also add some sort of filter onto it, but I'm not sure what would make sense.
Edit: How can I reduce the high frequency noise on this system?