[old_tv_nut]

You say the scope reading shows a linear range. Do you mean that the voltage is 20% at setting 2, 30% at 3 etc.? (Linear?) Variation should be logarithmic, starting out very small for an increment of say 1 to 2 or 2 to 3, but be relatively huge going from 8 to 9 to 10. If it's a similar size steps from 1 to 2 and 8 to 9, there's a problem with the volume control circuit.