Sealed Potentiometer Lubrication

[Jeff Liebermann]

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
<http://802.11junk.com/jeffl/crud/SSI3000b.jpg>
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Smitty Two]

In article <76eti551cr28acp4cu0u1f8s7tsgqdfks5@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

 

[Rheilly Phoull]

"Smitty Two" <prestwhich@earthlink.net> wrote in message
newsrestwhich-9F3087.17124920122009@newsfarm.iad.highwinds-media.com...

In article <76eti551cr28acp4cu0u1f8s7tsgqdfks5@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

Umm, did the op say he was putting OIL in the pots ??
That should settle the matter
--
Regards .............. Rheilly P

 

[bob urz]

Jeff Liebermann wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?


My method of doing this is to get a pencil soldering iron with small

long tip. Melt a hole in the case carefully and slowly. When you break
through, be sure to turn the pot back and forth so the slag does not jam
the pot. Then spray Caig pro gold or such into the hole and work the pot
back and forth. I usually melt the hole opposite the terminals if
possible allowing room for the resistance film.

bob

 

[hr(bob) hofmann@att.net]

On Dec 20, 8:31 pm, "Rheilly Phoull" <rhei...@bigslong.com> wrote:

"Smitty Two" <prestwh...@earthlink.net> wrote in message

newsrestwhich-9F3087.17124920122009@newsfarm.iad.highwinds-media.com...





In article <76eti551cr28acp4cu0u1f8s7tsgqdf...@4ax.com>,
Jeff Liebermann <je...@cruzio.com> wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers.  For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent.  In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner.  Not these sealed pots.  I've
tried my home made adapter over the threads to pump oil under pressure
into the pot.  That sorta works for the first pot, but many of these
pots are multi-section.  If they were screwed together, I would try
tearing one apart, but these use rivets.  I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations?  Drill a hole in the
side somewhere?  Where?

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

Umm, did the op say he was putting OIL in the pots ??
That should settle the matter
--
Regards .............. Rheilly P- Hide quoted text -

- Show quoted text -

I use a hypodermic needle, like I use to refill ink cartridges, filled
with Naptha to restore nosiy pots. Usually works, maybe 90% of the
time. THe Naptha penetrates into almost anything.

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:76eti551cr28acp4cu0u1f8s7tsgqdfks5@4ax.com:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot.

that washes away the shaft grease,right into the pot.

That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

when I was working at TEK field service centers,that is exactly what I used
to do. I made up a fiberglass rod with a coupler on the end holding a small
drill bit(to get into tight areas without taking apart the whole scope),and
hand-drilled small holes in the sides of the black Bourns modpots
(multisection!). I had taken one apart to find the best place to drill
without hitting the rotor,and you have to be careful when you're just about
to break thru,and pull OUT the last bit of plastic so it doesn't get
carried into the pot.Then I fixed a hypo needle to the plastic spray tube
on the tuner/lube TEK used to supply,and after the spray cans of that went
away,I made up a spray can with a brass fitting from an old inner tube
soldered to the top,so I could fill the can with TEK's cleaner-lube that
came in a bottle,it had Cramolin in it,along with some Freon solvent.Then I
could pressurize it with a bicycle pump.The needle slipped easily into the
small drilled hole,and a squirt would do the job. I didn't bother resealing
the hole.
It worked very well,and saved customers a lot of money,and me a lot of
time.



--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jim Yanik]

"Rheilly Phoull" <rheilly@bigslong.com> wrote in
news:kNGdnYAf5MqwQ7PWnZ2dnUVZ_judnZ2d@westnet.com.au:

"Smitty Two" <prestwhich@earthlink.net> wrote in message
newsrestwhich-9F3087.17124920122009@newsfarm.iad.highwinds-media.com...
In article <76eti551cr28acp4cu0u1f8s7tsgqdfks5@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

easier said than done.

Umm, did the op say he was putting OIL in the pots ??
That should settle the matter

I now use Radio Shack's tuner cleaner/lube 64-4315

it contains mineral oil.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jeff Liebermann]

On Sun, 20 Dec 2009 21:51:22 -0600, Jim Yanik <jyanik@abuse.gov>
wrote:

I've
tried my home made adapter over the threads to pump oil under pressure
into the pot.

that washes away the shaft grease,right into the pot.

There seems to be a rubber O-ring or other seal inside. I couldn't
get very much cleaner past it. I don't think there's any grease left
in the old pots, but you're probably right about it for fairly new
pots.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

when I was working at TEK field service centers,that is exactly what I used
to do. I made up a fiberglass rod with a coupler on the end holding a small
drill bit(to get into tight areas without taking apart the whole scope),and
hand-drilled small holes in the sides of the black Bourns modpots
(multisection!).

I was going to use a Dremel drill, but I guess you're a drill in a pin
vice should give better control. Thanks for saving me from that
disaster.
<http://www.amazon.com/Bergeon-Double-Sided-Vice-Small/dp/B000E8BO9E>
That main thing is that you've confirmed that drill and squirt is the
most practical way to deal with this.

I had taken one apart to find the best place to drill
without hitting the rotor,and you have to be careful when you're just about
to break thru,and pull OUT the last bit of plastic so it doesn't get
carried into the pot.

Good point. Any clue as to the best place to drill? Obviously on one
of the sides.

Then I fixed a hypo needle to the plastic spray tube
on the tuner/lube TEK used to supply,

I have plenty of syringes and the usual electronics chemistry set. I
like to use alcohol to do the initial cleaning followed by a drop or
two of mineral oil. The big advantage is that it doesn't soften most
plastics. I have some Cramolin, so maybe that's a better cleaner
(because it removes various oxides).

and after the spray cans of that went
away,I made up a spray can with a brass fitting from an old inner tube
soldered to the top,so I could fill the can with TEK's cleaner-lube that
came in a bottle,it had Cramolin in it,along with some Freon solvent.Then I
could pressurize it with a bicycle pump.The needle slipped easily into the
small drilled hole,and a squirt would do the job.

Clever, but I don't plan to make this exercise a regular habit. A
simple syringe should work except for awkward locations. Also, it's
fun terrorizing visitors and customers with my collection of syringes.

I didn't bother resealing
the hole.
It worked very well,and saved customers a lot of money,and me a lot of
time.

Thanks much. I'll try it after I find and dissect an old pot to see
where to drill.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sun, 20 Dec 2009 17:12:49 -0800, Smitty Two
<prestwhich@earthlink.net> wrote:

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

I don't mind drilling out the rivets. It's the rest that has me
worried. There are 4 rivets per pot. I just counted 12 pots per
instrument. I have 3 Wavetek/SSI 3000b service monitors to fix:
<http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html>
all of which have the same problem with intermittent pots. That's 144
rivets. Drilling is the easy part. How am I suppose to get them back
together? I'm not sure but the rivet holes appear even smaller than a
0-80 screw. In any case, neither the screw head or the nut will fit
as there's no clearance between the pot face plate, and the front
panel of the service monitor.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Mon, 21 Dec 2009 10:31:45 +0800, "Rheilly Phoull"
<rheilly@bigslong.com> wrote:

Umm, did the op say he was putting OIL in the pots ??
That should settle the matter

Yes, I did. A different problem with many pots is rust, dirt, dust,
and crud causing the shaft to jam or turn roughly. There are various
ways to lube the shaft, but one of the easiest is an adapter that
screws onto the mounting threads, which directs the oil around the
shaft under pressure:
<http://www.customguitars.com/pots.html>
I built my own, which is similar to the one in the photo except that
it's brass, longer, and ends in a bicycle valve. I run some solvent
(usually just alcohol) through the pot first, then follow it with some
oil or grease. Incidentally, I've had some spectacular failures from
using too much pressure.

What I tried to do unsuccessfully was to use the same device to
deliver a load of contact cleaner into the Mod Pot sealed
potentiometers using the aformentioned device. It didn't work.

Hopefully, that should settle your manner.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Sun, 20 Dec 2009 18:45:08 -0800 (PST), "hr(bob) hofmann@att.net"
<hrhofmann@att.net> wrote:

I use a hypodermic needle, like I use to refill ink cartridges, filled
with Naptha to restore nosiy pots. Usually works, maybe 90% of the
time. THe Naptha penetrates into almost anything.

Coleman white gas camp fuel is basically naptha. Is that what you
use? Seems a bit strong and overkill to me for pot cleaning.

I have two friends that are diabetics that give me some of their old
syringes. I grind off the sharp point with bench grinder, and clean
up the burr by polishing and forcing a fine stainless wire down the
bore. The syringe needle is much shorter than the common ink
cartridge fill syring, but is also much smaller diameter, which is
useful in tight places or through small holes. It looks like this:
<http://www.elitemedical.com/monoject.html>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Smitty Two]

In article <h9uti59opkb3g5dkiuki2bpkv7qab98ae5@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:

On Sun, 20 Dec 2009 17:12:49 -0800, Smitty Two
prestwhich@earthlink.net> wrote:

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

I don't mind drilling out the rivets. It's the rest that has me
worried. There are 4 rivets per pot. I just counted 12 pots per
instrument. I have 3 Wavetek/SSI 3000b service monitors to fix:
http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html
all of which have the same problem with intermittent pots. That's 144
rivets. Drilling is the easy part. How am I suppose to get them back
together? I'm not sure but the rivet holes appear even smaller than a
0-80 screw. In any case, neither the screw head or the nut will fit
as there's no clearance between the pot face plate, and the front
panel of the service monitor.

Well, I guess you could rivet them back together. By the way, regarding
syringes, you don't have to grind off hypodermic needles. You can easily
buy dispensing syringes, and needles in any diameter and a variety of
lengths.

Agree that you're facing a big job, and one fraught with potential
danger.

 

[N_Cook]

Jeff Liebermann <jeffl@cruzio.com> wrote in message
news:h9uti59opkb3g5dkiuki2bpkv7qab98ae5@4ax.com...

On Sun, 20 Dec 2009 17:12:49 -0800, Smitty Two
prestwhich@earthlink.net> wrote:

As a friend's father used to say, "I've never been intimidated by a
rivet." Drill them out, replace with screws to reassemble.

I don't mind drilling out the rivets. It's the rest that has me
worried. There are 4 rivets per pot. I just counted 12 pots per
instrument. I have 3 Wavetek/SSI 3000b service monitors to fix:
http://802.11junk.com/jeffl/pics/home/slides/BL-shop5.html
all of which have the same problem with intermittent pots. That's 144
rivets. Drilling is the easy part. How am I suppose to get them back
together? I'm not sure but the rivet holes appear even smaller than a
0-80 screw. In any case, neither the screw head or the nut will fit
as there's no clearance between the pot face plate, and the front
panel of the service monitor.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Use fine ni-chrome heater element wire (stronger than Cu for fine wire) ,
straightened out , through the holes and twist up tight - who else is going
to peer in there ?

From my experience of cubic form / rivetted pots is problem due to too much
lubrication, it bleeds, over time, from the bush area grease down onto the
track degraded to an oil, open up and clean out with meths


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:bftti5d0vuvdqhatdfnmdcuuq1ek7qo67g@4ax.com:

On Sun, 20 Dec 2009 21:51:22 -0600, Jim Yanik <jyanik@abuse.gov
wrote:

I had taken one apart to find the best place to drill
without hitting the rotor,and you have to be careful when you're just
about to break thru,and pull OUT the last bit of plastic so it doesn't
get carried into the pot.

Good point. Any clue as to the best place to drill? Obviously on one
of the sides.

On the black modpots,the resistive element is brown,and is exposed on one
side,and I drill about 3/32" (rough guess from memory) back from the brown
element,on the centerline.The case is circular on the inside,so
centerline is the thinnest part.

I didn't have much success with the blue modpots that were riveted
together.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Jim Yanik]

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:tbvti5df7er78fd6428f6r8mg0fdb8al3l@4ax.com:

On Sun, 20 Dec 2009 18:45:08 -0800 (PST), "hr(bob) hofmann@att.net"
hrhofmann@att.net> wrote:

I use a hypodermic needle, like I use to refill ink cartridges, filled
with Naptha to restore nosiy pots. Usually works, maybe 90% of the
time. THe Naptha penetrates into almost anything.

Coleman white gas camp fuel is basically naptha. Is that what you
use? Seems a bit strong and overkill to me for pot cleaning.

may attack the plastic. use a standard tuner cleaner/lube spray.

I have two friends that are diabetics that give me some of their old
syringes. I grind off the sharp point with bench grinder, and clean
up the burr by polishing and forcing a fine stainless wire down the
bore. The syringe needle is much shorter than the common ink
cartridge fill syring, but is also much smaller diameter, which is
useful in tight places or through small holes. It looks like this:
http://www.elitemedical.com/monoject.html

I used my Dremel to grind off the sharp on the needle.
a cutoff disc will work fine.I didn't use a really fine needle,maybe 1mm.

--
Jim Yanik
jyanik
at
localnet
dot com

 

[Meat Plow]

On Sun, 20 Dec 2009 16:00:25 -0800, Jeff Liebermann
<jeffl@cruzio.com>wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

Force it down the shaft.

 

[Charles]

30 years old ... they are probably worn out.

 

[Shaun]

"bob urz" <sound@inetnebr.com> wrote in message
news:hgmnp0$fv8$1@aioe.org...

Jeff Liebermann wrote:
How does one lube a sealed pot? I have several instruments and two
scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?


My method of doing this is to get a pencil soldering iron with small long
tip. Melt a hole in the case carefully and slowly. When you break
through, be sure to turn the pot back and forth so the slag does not jam
the pot. Then spray Caig pro gold or such into the hole and work the pot
back and forth. I usually melt the hole opposite the terminals if possible
allowing room for the resistance film.

bob

Bob,

Do you mean melt the hole at the back of the pot??

Shaun

 

[GregS]

In article <76eti551cr28acp4cu0u1f8s7tsgqdfks5@4ax.com>, Jeff Liebermann <jeffl@cruzio.com> wrote:

How does one lube a sealed pot?

I have several instruments and two scanners that use rectangular
shaped, sealed potentiometers. For example, this is an SSI/Wavetek
3000b service monitor that has about 10 of these pots on the front
panel:
http://802.11junk.com/jeffl/crud/SSI3000b.jpg
After about 30 years use, all the pots (and I do mean all) are
intermittent. In a non-sealed pot, it's easy enough to clean and
lubricate it with some contact cleaner. Not these sealed pots. I've
tried my home made adapter over the threads to pump oil under pressure
into the pot. That sorta works for the first pot, but many of these
pots are multi-section. If they were screwed together, I would try
tearing one apart, but these use rivets. I might also be tempted to
replace the pots, but there are just too many of them.

So, how does one lube one of these abominations? Drill a hole in the
side somewhere? Where?

I frequently just spray the outside with some very light stuff.
I have used Bullfrog cleaner that has high vapors. I also
just use alcohol maybe with a little light oil. It works
sometimes. Most pots can be taken apart, but I have drilled holes
before. Sometimes it takes a day or two to settle in.

greg

 

[Jeff Liebermann]

On Mon, 21 Dec 2009 20:30:38 -0500, "Charles"
<charlesschuler@comcast.net> wrote:

30 years old ... they are probably worn out.

Chuckle... please pardon my amusement. There are various ways for
pots to fail, but for test equipment, wearing out the resistance
material or contacts is not one of them. What seems to be happening
here is that the grease, oil, or lube used in the pots, mixes with
surface scrapings from the resistance material, and turns to tar.
Given sufficient time, it hardens into a mound of goo on the
resistance material, which causes a "bump" in the rotation. In less
extreme cases, the tar is spread over most of the pot, resulting in a
"noisy" pot.

Over the years, I've notice that test equipment pots that have *NOT*
been used much, are the ones must susceptible to the aforementioned
failure. In my case, I have 3 out of 20 adjustments on the front
panel that work just fine. These are the pots that I use most (signal
level, deviation, volume). However, the other 17 assorted adjustments
rarely get moved and have now become a major problem.

I haven't had time to drill and lube my service monitor quite yet.
I'll do it in the next few days.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558