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<blockquote data-quote="Tim McCulloch" data-source="post: 89086" data-attributes="member: 67">Re: PM4000 trouble shooting helpOne of our 4Ks developed a hum after it kept tipping... and landed lid-down on the floor.&nbsp; We tried a bunch of stuff and got rid of about 80% of the noise.For us, it appeared that the chassis ground was no longer 100% intact.&nbsp; We took a ScotchBrite® pad and cleaned all of the metal-to-metal contact surfaces, sprayed DeOxIt and re-seated all the ribbon connectors.&nbsp; But the remaining low level hum was still there and worsened when there is anything remotely Pin 1 related.&nbsp; I recall finding a loose XLRM output connector that, upon regaining intimate contact with the sheet metal, quieted things down some as well.&nbsp; Or we may have just moved some wires around that needed moving....That all said, I think you&#039;re on the right track.&nbsp; I recall being told that the 4K would tolerate hot-swapping of modules but it&#039;s been so long ago that I can&#039;t remember who told me that.&nbsp; It&#039;s probably worth a power cycle to not screw up things any worse.&nbsp; Try pulling all the input modules and see if you have the hum.&nbsp; If it&#039;s still there you can eliminate a lot of PC board inspection...A final thought - both of the PSUs are likely about the same age.&nbsp; I suppose it is possible to have bad voltage regulators and/or filter caps by now.Maybe JR can give us a designer&#039;s view of potential causes.</blockquote>

[QUOTE="Tim McCulloch, post: 89086, member: 67"] Re: PM4000 trouble shooting help One of our 4Ks developed a hum after it kept tipping... and landed lid-down on the floor. We tried a bunch of stuff and got rid of about 80% of the noise. For us, it appeared that the chassis ground was no longer 100% intact. We took a ScotchBrite® pad and cleaned all of the metal-to-metal contact surfaces, sprayed DeOxIt and re-seated all the ribbon connectors. But the remaining low level hum was still there and worsened when there is anything remotely Pin 1 related. I recall finding a loose XLRM output connector that, upon regaining intimate contact with the sheet metal, quieted things down some as well. Or we may have just moved some wires around that needed moving.... That all said, I think you're on the right track. I recall being told that the 4K would tolerate hot-swapping of modules but it's been so long ago that I can't remember who told me that. It's probably worth a power cycle to not screw up things any worse. Try pulling all the input modules and see if you have the hum. If it's still there you can eliminate a lot of PC board inspection... A final thought - both of the PSUs are likely about the same age. I suppose it is possible to have bad voltage regulators and/or filter caps by now. Maybe JR can give us a designer's view of potential causes. [/QUOTE]

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