Crate FXT-65 Buzzing In DSP Effects Loop

[Bamba]

Hello everyone! This is my first time on this forum and I’m hoping someone can help me out here. The problem is pretty simple to understand, but not too easy to troubleshoot with my limited knowledge on the subject. I recently bought a Crate FXT-65 with DSP and when I tested it at the store it was working flawlessly so I picked it up for $60. However when I got it home, after a pretty docile trip with no severe bumps, it had a hum when I turned up the DSP Level knob. The sound gets louder as I turn the Level knob up and the effects apply to the hum if that matters. The strange thing, at least to me, is that the hum does not happen when nothing is plugged in. It only occurs when an audio jack is plugged into it, with or without an instrument connected. I have tested it with multiple guitars and cords and it happens every time. I have given as much information as possible at the moment, but I’ll be happy to answer any questions. Thanks in advance for any suggestions!

[The Dude]

Here's the schematic, although it doesn't show the DSP board.

https://music-electronics-forum.com/...9&d=1232848572

On the first page, there is a TP16 (10VDC with .5V ripple), which is supply for the DSP board. It might be that you've lost filtering on that supply. Check for more than .5V ripple on that line. Check that solder is good on C64. If solder is good and you've got excessive ripple at the test point, try changing the cap.