Concert Bass Mid control not working

[Hd0521]

With the mids dimed and the bass and treble at zero there is a very low volume tone coming through. If I back the mids down to zero the volume of that tone doesn’t change. If I dime either bass or treble the volume increases. I’m assuming it’s a passive Eq stack. I opened the amp up and it looks like the original pots wired right to the board. Any solution before having the pot replaced?

[_peter]

Hi,

according to this schematic: https://schematicheaven.net/newamps/sunn_concertbass.pdf
the bass pot isn't stacked on the mids pot as in the usual fender/marshall tonestacks.
With bass at zero, the signal at the mids pot is shorted to ground. Therefor the mids pot can't work in this situation.

Cheers,
Peter