"Jeff Liebermann"


Try taking apart the pots in a joystick. They get far more use than
any front panel control pot. I've seen them with grooves worn into
the carbon that match the individual fingers of the slider. I've also
seen the same thing in volume control knobs on 2way radios that
require turning the volume control to power on/off the radio. If you
leave such a worn grooved pot in place for a long time, the
lubricating grease will "migrate" into the grooves. When that
happens, the individual fingers will float on top of the grease, and
not make contact with the carbon, resulting in an intermittent. With
flat carbon, the fingers will push the grease out of the way. With a
grove in the carbon, the fingers will push the grease into the
grooves.

This also has caused me some grief in the distant past, where I would
"lube" a pot to break loose the shaft, and get the radio back with an
intermittent volume control a few months later. However, all this is
for high use 2way radio controls. I doubt that any hi-fi or even
commodity radio control would see sufficient use (or abuse) to put
grooves in the carbon.


** I service mostly " pro audio " which includes mixing desks and the
special mixers used by DJs.

DJ mixers have a "cross-fader " that allows a pair of stereo channels to be
mixed in any proportion. Most DJs work the ring of the things - so much so
that it is standard practise make the cross-fader a "user replaceable"
module fitted on sub panel that slots into the main panel.

Nothing unusual to see cross-faders ( and channel faders) with all the tips
worn off the fingers and deep grooves in the carbon track - right down to
the phenolic backing.

Most control pots these days have the carbon track deposited on the backing
material rather the old method of using a solid, moulded track and attaching
it to a backing.

Deposited tracks are very much thinner and wear out much sooner.



.... Phil