Mesa Boogie Mark III scratchy Volume pot.

[Guitarist4life]

Hello,
I was wondering if you guys could help me get on the right track to fix my mesa/boogie mark III.
The "clean" channel volume pot is very scratchy and the amp would get quieter from 2 to 5 o' clock, so I replaced it with a new push/pull pot of the same value.
The new pot does exactly the same thing as the old pot.. scratchy and loss of volume after 2 o clock.. All electrolytic caps seem fine.. no leaks or swollen (they were replaced some time ago by the previous owner). Any idea what I should look for? I would greatly appreciate your help.

[Chuck H]

Three possibilities I can guess at. Bad preamp tube, leaky coupling cap in the tonestack or the LDR in that circuit is leaking voltage onto the circuit from it's power supply.

http://www.tubefreak.com/fschema.htm

[g1]

The items Chuck mentioned would put DC on the pot, which makes them sound scratchy. You can also check with a meter to see if there is DC on any of the pot legs.
Other than that, it's possible you have an oscillation, which could also cause scratchy noises, and loss of volume as pot is raised.