C|24 Diagnose Problem of Low Thud Through Sub Output Channel 3 Only

[Willard]

Oops. Previously posted this in the "Control|24" forum.

I have a C|24, purchase late 2007. In the past month I’ve been getting a low pulse/thud (about 50bpm) through the sub. Here’s the details.

Channels 1 and 3 out of C|24 connected to KRK S10. Then feeding through from the KRK S10 to two KRK v6s.
I hear the low pulse/thud in the sub only.
I only hear the thud from channel three, not channel one.
Pro Tools (9) is not booted at the time.
When Pro Tools is booted, changing the volume does not change the volume of the low pulse/thud, it’s constant.

The C|24 seems to operate normally, nothing unexpected.
If I power down the C|24, I no longer hear the pulse/thud.

My guess is that it is the power supply, but would like to hear from anyone who has had similar issues or can suggest any trouble shooting I haven’t thought of.

Thanks

[Willard]

I wrote to Skynet (makers of the PSU) and asked them if this sounded familiar. They said it did not, but they would diagnose my PSU for a $50 fee. That wouldn't be a problem if I was at all confident I'm heading in the right direction. Don't want to be without the C|24 if I can at all avoid it.

[Craig F]

power supply I would expect to hear it in all channels
how comfortable are you opening up your unit and looking/sniffing for a damaged part
I would look at the ch3 output buffer amp back tracking to the volume control section
also look at the PSU when you have it open

[Willard]

@ Craig F. Thanks for your thoughts. Essentially you're concurring with Skynet, which is helpful.

I'm very comfortable taking things apart, so I'll give that a go just to see if there's something obvious to the naked eye. I think this will likely result in my having to take it in somewhere here in LA.