The Ernie Ball volume pedals often become scratchy after a long time of usage. While you can replace the current poti model with a brand new poti, it is almost impossible to get a replacements for the older poti types. However, the older potis can be opened and cleaned which – not always but often – cures the scratching. As I did this successfully a few days ago, I took some pictures to demonstrate the procedure.
The poti was the Canadian type used in the mid 90ies but the previous Allen Bradley / Clearostat poti used before can be treated in the same way.
First, I recommend to remove the two screws that hold the black metal block which holds the poti. The string can be released from the poti easily then (you might take pictures before so that later you know how it was assembled).
With these poti types, the wires are plugged to the poti and can be removed without any soldering (again, take notes where they were, or take a picture).
Now the poti should be clean. Note that disassembling the wiper from the carbon resistor is not possible with these poti models so you need to clean it like this. Mount the case again, bend down the tabs to close it. An instruction how to assemble the string again can be found in this video:
Note that you can clean a modded volume pedal in the same way, just make sure to assemple all wires and the string exactly as they were before!!
Another note on this topic: I meanwhile tend to believe that the different taper on Mark Knopfler’s volume poti is not due to a different poti model but to an electronic solution possibly built into his rack. A first prototype circuit works promising, and also avoids the noise of a scratchy poti electronically. Watch out for future updates, I hope to offer something here soon.