Topics

Stuck switches on 453


Richard P
 

I’ve used my Model 453 for years for basic audio but it has always had a problem. The rotary switches on each of the variable sweep rate potentiometers (one on the front panel, and one on the side) are frozen in the uncalibrated positions. Therefore, the “Uncal A or B” light is forever lit, and the sweep rate for either A or B is uncalibrated. These combined switch/potentiometers are like a rotary volume control with an on/off switch. But stuck. I’ve tried to loosen them up with DeOxit, contact cleaner, even liquid wrench. But these guys are pretty-well sealed up, and access to them in the 453 chassis is very challenging. I can see the shafts moving a bit, so I believe the problem is inside the switch/pot assemblies, not that shafts are stuck in bushings. Any thoughts on this one?

Richard


Abc Xyz
 

Richard,

I know a guy who told me he immerses Stuck Potentiometers/Switches in
Solution to free them up. I personally have not Witnessed the
Procedure...so take it for what its worth.
Also, I have Read where one Drills a Very Small Hole in the Body of the
Mechanism and Dribbles Solution in...again, I have never tried it or seen
it done.
I have tried turning the Scope where the Potentiometer Shaft is Vertical
and place a Few Drops of Deoxit on the Shaft itself thinking Gravity would
pull the Cleaner down into the Part...didn't work for me but it may be one
of those things where a Great Deal More Patience is Needed!

JR

On Thu, Jul 30, 2020, 10:46 PM Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

I’ve used my Model 453 for years for basic audio but it has always had a
problem. The rotary switches on each of the variable sweep rate
potentiometers (one on the front panel, and one on the side) are frozen in
the uncalibrated positions. Therefore, the “Uncal A or B” light is forever
lit, and the sweep rate for either A or B is uncalibrated. These combined
switch/potentiometers are like a rotary volume control with an on/off
switch. But stuck. I’ve tried to loosen them up with DeOxit, contact
cleaner, even liquid wrench. But these guys are pretty-well sealed up, and
access to them in the 453 chassis is very challenging. I can see the shafts
moving a bit, so I believe the problem is inside the switch/pot assemblies,
not that shafts are stuck in bushings. Any thoughts on this one?

Richard




Gary Robert Bosworth
 

Be extremely careful when drilling into potentiometers. You will almost
always drill into the resistive wire or element and ruin the pot. I cannot
stress this enough. Gary

On Fri, Jul 31, 2020, 07:21 Abc Xyz <yawrdanza@...> wrote:

Richard,

I know a guy who told me he immerses Stuck Potentiometers/Switches in
Solution to free them up. I personally have not Witnessed the
Procedure...so take it for what its worth.
Also, I have Read where one Drills a Very Small Hole in the Body of the
Mechanism and Dribbles Solution in...again, I have never tried it or seen
it done.
I have tried turning the Scope where the Potentiometer Shaft is Vertical
and place a Few Drops of Deoxit on the Shaft itself thinking Gravity would
pull the Cleaner down into the Part...didn't work for me but it may be one
of those things where a Great Deal More Patience is Needed!

JR

On Thu, Jul 30, 2020, 10:46 PM Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

I’ve used my Model 453 for years for basic audio but it has always had a
problem. The rotary switches on each of the variable sweep rate
potentiometers (one on the front panel, and one on the side) are frozen
in
the uncalibrated positions. Therefore, the “Uncal A or B” light is
forever
lit, and the sweep rate for either A or B is uncalibrated. These combined
switch/potentiometers are like a rotary volume control with an on/off
switch. But stuck. I’ve tried to loosen them up with DeOxit, contact
cleaner, even liquid wrench. But these guys are pretty-well sealed up,
and
access to them in the 453 chassis is very challenging. I can see the
shafts
moving a bit, so I believe the problem is inside the switch/pot
assemblies,
not that shafts are stuck in bushings. Any thoughts on this one?

Richard






n4buq
 

If those are Clarostat pots, I have had good success just disassembling, cleaning, and reassembling those.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Gary Robert Bosworth" <@grbosworth>
To: TekScopes@groups.io
Sent: Friday, July 31, 2020 1:58:55 PM
Subject: Re: [TekScopes] Stuck switches on 453

Be extremely careful when drilling into potentiometers. You will almost
always drill into the resistive wire or element and ruin the pot. I cannot
stress this enough. Gary

On Fri, Jul 31, 2020, 07:21 Abc Xyz <yawrdanza@...> wrote:

Richard,

I know a guy who told me he immerses Stuck Potentiometers/Switches in
Solution to free them up. I personally have not Witnessed the
Procedure...so take it for what its worth.
Also, I have Read where one Drills a Very Small Hole in the Body of the
Mechanism and Dribbles Solution in...again, I have never tried it or seen
it done.
I have tried turning the Scope where the Potentiometer Shaft is Vertical
and place a Few Drops of Deoxit on the Shaft itself thinking Gravity would
pull the Cleaner down into the Part...didn't work for me but it may be one
of those things where a Great Deal More Patience is Needed!

JR

On Thu, Jul 30, 2020, 10:46 PM Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

I’ve used my Model 453 for years for basic audio but it has always had a
problem. The rotary switches on each of the variable sweep rate
potentiometers (one on the front panel, and one on the side) are frozen
in
the uncalibrated positions. Therefore, the “Uncal A or B” light is
forever
lit, and the sweep rate for either A or B is uncalibrated. These combined
switch/potentiometers are like a rotary volume control with an on/off
switch. But stuck. I’ve tried to loosen them up with DeOxit, contact
cleaner, even liquid wrench. But these guys are pretty-well sealed up,
and
access to them in the 453 chassis is very challenging. I can see the
shafts
moving a bit, so I believe the problem is inside the switch/pot
assemblies,
not that shafts are stuck in bushings. Any thoughts on this one?

Richard








Richard P
 

Gents,

Thanks, all. I really don’t know if it’s the pot, or the combined switch, that is frozen. One or the other. I can get spray into the pot, but it still won’t move. The rotary switch on the back, however, is sealed tightly. I will continue to attempt to get spray into the fool switches. There are two of these combined pot/switches in the 453. Stay tuned.

Richard


Harvey White
 

If you can loosen the coupler on the switch, perhaps the pot shaft can rotate?  That might narrow it down.

Harvey

On 7/31/2020 6:04 PM, Richard P via groups.io wrote:
Gents,

Thanks, all. I really don’t know if it’s the pot, or the combined switch, that is frozen. One or the other. I can get spray into the pot, but it still won’t move. The rotary switch on the back, however, is sealed tightly. I will continue to attempt to get spray into the fool switches. There are two of these combined pot/switches in the 453. Stay tuned.

Richard



n4buq
 

I recently worked on a larger rotary switch on a piece of an old Fluke calibrator. The dried grease can really make those shafts quite hard to turn! The HP 8640B has a similar issue with its band switch and it is amazing how much better they work when cleaned and freshly lubricated.

Good luck with it.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Richard P via groups.io" <wb5nen=yahoo.com@groups.io>
To: TekScopes@groups.io
Sent: Friday, July 31, 2020 5:04:37 PM
Subject: Re: [TekScopes] Stuck switches on 453

Gents,

Thanks, all. I really don’t know if it’s the pot, or the combined switch,
that is frozen. One or the other. I can get spray into the pot, but it still
won’t move. The rotary switch on the back, however, is sealed tightly. I
will continue to attempt to get spray into the fool switches. There are two
of these combined pot/switches in the 453. Stay tuned.

Richard




dabono@...
 

I came across a similar problem recently on a T922. In my case, the variable knobs for the channel 1 and channel 2 Volts/Div were frozen (and the shaft coupling on the CH2 knob was broken, probably from somebody trying to force it).

I was able to get them working again by spraying a little contact cleaner where the potentiometer shaft goes into the "sleeve" on the potentiometer body, and gradually turning them back and forth several times. They were very stiff at first, but eventually needed less force to turn them, and they'd rotate a bit further each time. I didn't need to do anything to the switches behind the pots.

I don't know if you tried contact cleaner in that particular spot - if not, it's worth a try.

Good luck!
David


Dale H. Cook
 

On 7/31/2020 10:20 AM, JR wrote:

I have tried turning the Scope where the Potentiometer Shaft is Vertical
and place a Few Drops of Deoxit on the Shaft ...
DeoxIT is not intended for potentiometers - it is for switches. Caig FaderLube is intended for potentiometers and other controls.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/


Richard P
 

David (and others):

Yes, my problem is the same as yours: The variable knobs on Ch. 1 and 2 Volts/Div are frozen, and are stuck in the uncalibrated mode. I’ve tried various compounds...some for switches, some for pots, but no joy. Colorful Anglo-Saxon expressions haven’t helped, either. Just NOT going to budge, either one of them. Don’t know if it’s switches or pots that are binding.

But, since I mostly want this scope in Calibrated mode (and not Uncalibrated, where it is locked-up now), I’m thinking I will just bypass the switches and live with it. That’s what I’m thinking.

R


Gary Robert Bosworth
 

So often, it is the grease that was used as a lubricant and the volatiles
evaporated leaving a dried up paste.

On Sat, Aug 1, 2020, 08:58 Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

David (and others):

Yes, my problem is the same as yours: The variable knobs on Ch. 1 and 2
Volts/Div are frozen, and are stuck in the uncalibrated mode. I’ve tried
various compounds...some for switches, some for pots, but no joy. Colorful
Anglo-Saxon expressions haven’t helped, either. Just NOT going to budge,
either one of them. Don’t know if it’s switches or pots that are binding.

But, since I mostly want this scope in Calibrated mode (and not
Uncalibrated, where it is locked-up now), I’m thinking I will just bypass
the switches and live with it. That’s what I’m thinking.

R




greenboxmaven
 

In addition to the volatiles evaporating, the grease or oil can oxidize into varnish. This is greatly enhanced by moisture. I have had great results for many years using synthetic engine oil such as Mobil 1 0W-15 and heat to liquify the varnish. Put a few drops of the oil on the shaft and bushing, them heat the shaft where it goes into the bushing with a soldering iron until the oil is sizzling, add more oil as needed to maintain the heat bridge to the shaft and bushing. Remove any plastic couplings, gears, or knobs that could be damaged by the heat before you start. Work the shaft back and forth carefully until it frees up, be patient, if you don't get results at first, be sure there is a drop of oil on the shaft where it enters the bushing and let it cool. It may require a few heating-cooling cycles with the oil applied before it frees up, once it does, flush the oil and crud out thoroughly and re-lubricate with the synthetic oil. Then, use a contact cleaner of your choice for the pot or switch contacts.

Bruce Gentry, KA2IVY

On 8/1/20 12:02 PM, Gary Robert Bosworth wrote:
So often, it is the grease that was used as a lubricant and the volatiles
evaporated leaving a dried up paste.

On Sat, Aug 1, 2020, 08:58 Richard P via groups.io <wb5nen=
yahoo.com@groups.io> wrote:

David (and others):

Yes, my problem is the same as yours: The variable knobs on Ch. 1 and 2
Volts/Div are frozen, and are stuck in the uncalibrated mode. I???ve tried
various compounds...some for switches, some for pots, but no joy. Colorful
Anglo-Saxon expressions haven???t helped, either. Just NOT going to budge,
either one of them. Don???t know if it???s switches or pots that are binding.

But, since I mostly want this scope in Calibrated mode (and not
Uncalibrated, where it is locked-up now), I???m thinking I will just bypass
the switches and live with it. That???s what I???m thinking.

R




Richard P
 

I barely managed to free up (a little) one of the two stuck potentiometer/switching knobs on the variable time/division control. (I see in an earlier post or two that I mistakenly started started saying it was the volts/div controls that were stuck. Wrong. It is time/div that are stuck. Regardless, it was a similar problem. It was stuck. Apologies.) Anyway, the “Uncal” light is off and things are working acceptably. I thank everyone for help. But boy, these guys are stuck! I can live with this.

Richard


Stephen
 

If this is of any help, I had something similar on a 7B71, 7000 series time base plug-in.
The VAR didn’t want to move at all. It was completely stuck. I ended up de-soldering the pot and freeing it from the shaft extension a bit. It turns out it was pushed way too much into it and, as a result, wasn’t moving. That wasn’t easy, but now it’s completely free, and working as it should.

I don’t know how yours is mounted, but I hope this help...