Re: Clean and Lubricate Pots in Tek 475


Eric
 

Greg i have to disagree with you on this one. Tektronix them selves used to
have a product called "no noise" this was actually replaced with wd40. A
can of wd40 actually has a tektronix part number. The tektronox part number
is 006-2574-00.

Eric


On Fri, Nov 6, 2020, 3:25 PM Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

On Fri, Nov 6, 2020 at 10:05 AM, Bill wrote:


I put a little Deoxid into them and tried to find the problem with the
stiffness and the "springback" of these pots with little success. For
some
reason I could not locate why they turn ok when apart BUT are stiff when
assembled.
It depends on the particular construction, which may vary a lot between
brands. styles, and grades. If you refurbish a pot and it still binds after
thorough cleaning and lubing, look at all the possible parts that can
deform with age and use. First, make sure the shaft isn't bent, which is
especially possible on 1/8" and smaller ones. Next, check the axial end
play. It should be able to move in and out at least a few .001" at any
rotational position. If not, then the whole thing is just too tight, likely
due to any rubber and plastic parts deteriorating or cold-flowing.

The definition and construction of a "sealed" pot varies. Fancier, better
grade ones may be more elaborate and include rubber gaskets between parts,
and a rubber shaft seal like an o-ring at the bulkhead, or on a neck cut in
the shaft. This is what tends to give the "springback" feel, due to
deterioration and swelling of the material. If you can find a fresh o-ring
equivalent to the original, replacing it should fix that problem. An
alternative is to just delete the o-ring - the benefit of the seal isn't
that big a deal anymore, in a benign hobby/lab environment. If the o-ring
is at the bulkhead, eliminating it will likely also increase the axial
play, possibly too much. You can try a thinner o-ring or add appropriate
shim washers to tweak it.

If there are no shaft seals, then look at any rubber gasket layers - the
rubber gets thinner over time under compression, so the whole assembly gets
shorter, reducing axial clearance inside. If there is a shim washer at the
bulkhead, you can try a thinner one or deleting it, but be aware the shim
is also part of the thrust bearing function, so the pot may run rougher
without it. If you can't effectively shorten the rotor assembly, then you
can lengthen the body by say making new gaskets with thicker or fresh
material, or adding shim washers between sections, around the screws.
Again, high grade environmental sealing is not that important anymore.

If there are no rubber parts at all to blame, then cold-flowing of the
plastic body parts is the likely cause. Study the construction and look at
all the options to either shorten the insides, or lengthen the outsides.

Ed





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