if the pot is not scratchy, might not need replacement,
maybe a wire got broke lose, or something got bummed up
from opening and closing the case for battery changes
that pot in the link shows a 20k somebody might have replaced
it with a guitar hot pot which range from 100k to 470k
100k being the norm for guitar
with a higher value it could mess with the sweep range
you owned this since new? or bought used?
just go to Guitar Center and ask to try out a 105Q and switch it out with yours.

just kidding don't do that.