Yamaha PM1000 console - Strange Noises!!!

[jazzcrisis]

My 24ch. Yamaha PM1000 console is making some very strange noises. Seems to be coming from the master modules...individual channels, auxes, etc are fine. Definitely originating pre-fader, and the unbalanced outputs and monitor outs have the same noise. Phantom power doesn't seem to have any effect, and I don't think the problem lies with any switches, pots, or faders, even though it kind of sounds like a constant scratchy pot noise. It's the same regardless of whether channels are assigned too.

The noise has been here for awhile, though it seems to have become worse after I recapped the power supply. The master modules also have new capacitors.

It's a crackly, whooshing sort of sound that's always there, but it gets better and worse intermittently, over the course of 20-30 seconds usually. It gets better for a few minutes if I turn the console off and back on, so I wonder if it has something to do with capacitors. I think I heard somewhere that bad tantalum caps can make odd noises...

It doesn't sound like a ground issue, but is there supposed to be a separate ground wire (not part of the molex connectors) going to the power supplies? My console didn't have any, but I have seen others that have. If so, where does that connect to? The schematics don't seem to indicate.

I'm attaching a sample of the noise.

Any ideas?

 

[hoodun]

sounds like caps. im having a similar issue and cant.trace it. its on all.modules? I would recap everything in the main section. then upgrade caps in the modules if you have not done so yet. check voktages on your transistors too.

 

[jazzcrisis]

The entire console has been recapped within the last year, same values too. The noise is only on the master modules, but it's odd that the noise is the same between all of them.  I did suspect the transistors, but I need to figure out how to check their voltages while the modules are in the console--that's kind of tricky to do.

 

[hoodun]

You could just replace all of the transistors on the master modules. It will probably take less time than troubleshooting and will at least ween that part out. I used MPSA18 and 2N3906 PNP.