10-31-2009, 11:20 AM
I think I'd try deoxit5 and swab the carbon ring gently with a q tip to clear away any crud. If the shaft seems stiff I would use a sparing amount of WD40 to loosen it up, again, blotting everything up carefully. If the shaft is binding in it's bushing, it can produce erratic results as the wiper bounces around on the carbon track. You can check for "open" spots by slowly turning the pot connected to an analog ohmmeter, and looking for jumps in the readings. You'll have to do this twice, once from each outer leg to the center leg.
Most of the high quality control contact wipers I have seen have several litle "fingers" that simultaneously press against the carbon track. Theory was, if one digs into and wears away the carbon, another will keep continuity. Looks like this control has had a lot of wear, and eventually there will be spots where all the fingers are rubbing against grooves in the carbon. Solution? If you can move just a hare left or right, they will find new paths in the unworn part of the carbon track, and thereby fix the problem, at least for a while. That is, if you can get the D**n thing apart, adjust it, and get it back together again in a reasonable amount of time. Some of the real good controls had a c-ring in the front of the control that allowed you to do this. If so, a tiny amount of lithium grease or phonolube should be wiped on the shaft after thorough cleaning, and before re-assembly.
1 meg audio taper pots are real easy to get, and unless there is something utterly bizzare about the shaft, a sub should be pretty easy to fix up.
Now for the lunatic solution: Get a modern control with a smaller od shaft, drill out the original shaft, gut the rest of the old pot, slip in the new pot with a drop of krazy glue, connect the leads, snap on the dust cover, and don't tell anyone about it. No, I haven't done that yet, I'm still working.
Most of the high quality control contact wipers I have seen have several litle "fingers" that simultaneously press against the carbon track. Theory was, if one digs into and wears away the carbon, another will keep continuity. Looks like this control has had a lot of wear, and eventually there will be spots where all the fingers are rubbing against grooves in the carbon. Solution? If you can move just a hare left or right, they will find new paths in the unworn part of the carbon track, and thereby fix the problem, at least for a while. That is, if you can get the D**n thing apart, adjust it, and get it back together again in a reasonable amount of time. Some of the real good controls had a c-ring in the front of the control that allowed you to do this. If so, a tiny amount of lithium grease or phonolube should be wiped on the shaft after thorough cleaning, and before re-assembly.
1 meg audio taper pots are real easy to get, and unless there is something utterly bizzare about the shaft, a sub should be pretty easy to fix up.
Now for the lunatic solution: Get a modern control with a smaller od shaft, drill out the original shaft, gut the rest of the old pot, slip in the new pot with a drop of krazy glue, connect the leads, snap on the dust cover, and don't tell anyone about it. No, I haven't done that yet, I'm still working.
