Fusion 550 channel switching help

[shock me]

Hi, really my first post here. Guitarist for many years. Now into bass. Been reading on here for a month or so. I have a used GK Fusion 550 I bought from MF.

When switching channels via the footswitch my master turns counterclockwise to (no volume). It stays there fighting me as I try to increase it.

The other settings rotate fine. Is it me or the amp?

[B-string]

Sounds like the amp. Either the processor or motor on the control. Contact jason@gallien.com for more info than I can offer. Don't have the problem with mine.