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Stabilant 22 Contact Enhancer Application Notes
App. Note 3 - Schadow & Equivalent Switches
Because of their modular design, ease of use, and reasonable cost,
the Schadow type FE switches have found extensive use both in home and
professional audio applications. However several problems with them have
shown up on older equipment. The silver plating tends to tarnish in some
locations, there was a potential for flux entry into some versions of the
switch, and the lubricant used seemed to deteriorate in time. While newer
versions have been designed and are being manufactured by ITT-Schadow,
there are still thousands of the newer type in use, and thousands of the
previous units in use at this time. Servicing of the switches usually involves
laborious disassembly followed by cleaning of the switch housing and floating
contacts on the slide assembly. The number of very small parts and springs
makes this operation rather difficult when large number of switches are
Other solutions that have been tried:
Dayton Wright Associates Ltd. started to use the Schadow type FE switches
in the early 1970's in the production of preamplifiers. Problems with the
switches led the to use such production precautions such as hand soldering
of the switch to the circuit board after all other components were soldered
in place, the use of flux-sealants hand-applied around the projecting PC-mount
pins, as well as the substitution of other lubricants for the one supplied
by the manufacturer. While all these things did increase the life of the
switches, the major improvement came with the development of Stabilant
22. Over several years, The Dayton Wright Group Ltd., developed a procedure
for treating the Schadow type FE switches without disassembly that has
cut down on the amount of service work and has proven quite satisfactory
in extended use. While the procedure is quite simple, for proper results
all the contaminants have to be removed and only a minimal film of Stabilant
22A should be applied.
There are two basic contaminant problems we have found with these switches.
Contamination during manufacture of the circuit-board assembly, and atmospheric
Unless the switches are of the type having a sealant applied to the
fixed contact (those fitted to the case body) the possibility exists for
flux to wick up into the interior of the switch assembly during the soldering
operation. Methods used to combat this, have ranged from adding the switch
units after the other components have been wave soldered in place, to the
use of solder preforms as a method of limiting the amount of flux that
can be applied to each pin. Sometimes, a slight amount of tarnish on the
PC contact can make soldering difficult and this, in turn, leads to an
excessive use of solder (and flux).
Because the plastics used did not withstand some of the vapor-phase
defluxing systems and were damaged by other solvent defluxers, some manufacturers
relied on a two phase system, a somewhat less aggressive defluxers followed
by a general washoff of the liquefied flux. The potential problem with
the latter was that it could leave a minuscule coating of flux over all
of the board's components. While this was rarely enough to cause problems
on exposed wiring and card-edge connectors, the semi-enclosed interiors
of the switches were more vulnerable as here the build-up was much greater.
Closed-rear push-button switches exhibit one trait in common, when they
are released, they tend to "inhale" some of the atmospheric contaminants
from the front-panel area, holding them inside the rear of the switch assembly
where they often precipitated onto the contact assemblies. Where electronic
equipment is used by smokers, there will be a gradual accumulation of tar
and nicotine within the switch, in concentrations much greater than found
on the other components. For the switch to function properly, both residual
flux and other contaminants have to be removed along with any spent lubricants.
Cleaning out the residual contaminants:
The procedure starts with flushing out the contaminants & lubricant
residue with isopropyl alcohol. We recommend the use of a 50cc syringe
with a 2 inch long needle. The needle can usually be inserted at the rear
of the switch between the stamped brown-phenolic wafer and the black molded
body. Insert the needle so that the hole is towards the body of the switch.
Working the switch, flush it out with about 10 to 20 cc's of isopropyl
alcohol. Depending upon the age of the switch, this may have to be done
a second time within a week to ten days as the hardened contaminants dissolve
in the newly applied Stabilant film and distribute themselves on the contact
surfaces. In any event all of these contaminants have to be removed for
the switches to work reliably once more, and solvents that would remove
all of the contaminants at the first shot could damage the plastic parts.
Remember that isopropyl alcohol is flammable and work should be done in
a well ventilated location.
Applying the Stabilant 22A:
Using a 1 cc disposable insulin type of syringe inject about 1/8 TO
1/6 cc (for a 2 or 4 pole) to 1/4 TO 1/3 cc (for a 6 to 1 0 pole) of Stabilant
22A into the rear of the switch. If this can be done with the switch in
an approximately horizontal position, it will minimize the loss of the
22A from the front of the switch while the alcohol evaporates. Obviously,
where a great number of switches are involved it is better to flush them
out all at once and then proceed with the addition of the Stabilant
22A Immediately, upon injection of the Stabilant 22A, vigorously
cycle the switch to distribute the material before the isopropyl alcohol
evaporates. Only a very thin film is needed on the contacts. If the film
is too thick, a phenomenon can occur called hydroplaning. This is where
motion of the switch pushes a wave of lubricant ahead of it gradually thickening
the film and widening the gap. This could delay the switch on of the contact
when instantaneous operation is needed. Generally, hydroplaning should
be suspect when it is the switches that are most often used that cause
problems, rather than the least used switches. The slight detergency action
of the Stabilant will lift much of the existing tarnish over a period
of time, holding it in solution. Normally this does not degrade the operation
of the switch. Some use prefer to repeat the procedure six to twelve months
later to remove the suspended tarnish.
Precautions and re-applications:
As noted, on equipment that has been in service some time, the detergency
action of the Stabilants may well loosen up so much detrius, and even residual
flux inside the switch that it might be necessary to re-flush-out the switch
and re-apply the Stabilants. The need for this will be shown up
if the treated switch becomes noisy once again within two to three weeks.
Remember, a# traces of the existing grease MUST have been removed as well!
Measurements on treated switches have shown a marked improvement of
the signal-to-noise ratio on signals, as well as a significant reduction
in total harmonic distortion. As an example, although the material has
been used on preamplifier switches. since the early 1980's no repeat lubrication
has proven necessary for units treated in that time indicating a useful
life in excess of five years..
CAUTION: A virtual copy of the ITT-Schadow switch is being manufactured
by TONELUCK(TM) and is now being used by Sony both in new equipment and
as replacements. The sealant used on these switches does not appear to
meet the usual standards for conformal coatings and may be damaged by many
of the solvents used in electronic service. We would strongly advise against
using any cleaner or contact treatment on these switches. They can be distinguished
by the name TONELUCK underneath the switch, their gray body and clear plastic
(rather than phenolic) top plate.
Stabilants are a product of Dayton Wright research & development and are made in Canada
NSCM/Cage Code - NATO Supply Code 38948
15 mL of S22A has NATO Part # 5999-21-900-6937
The Stabilants are patented in Canada - 1987; US Patent number 4696832. World-wide patents pending. Because the patents cover contacts treated with the material, a Point-of-sale License is granted with each sale of the material.
MATERIAL SAFETY DATA SHEETS ARE AVAILABLE ON REQUEST
Stabilant, Stabilant 22, and product type variations thereof are Trade Marks of D.W. Electrochemicals Ltd.
© Copyright 2003 - D.W. Electrochemicals Ltd. This note may be reproduced or copied, provided its content is not altered. The term "contact enhancer", © 1983 Wright Electroacoustics.
NOTICE: This Application Note is based on customer-supplied information, and D.W. Electrochemicals is publishing it for information purposes only. In the event of a conflict between the instructions supplied by the manufacturer of the equipment on which the Stabilant material was used, and the service procedure employed by our customer, we recommend that the manufacturer be contacted to make sure that warranties will not be voided by the procedures.
While to our knowledge the information is accurate, prospective users of the material should determine the suitability of the Stabilant materials for their application by running their own tests. Neither D.W. Electrochemicals Ltd., their distributors, or their dealers assume any responsibility or liability for damages to equipment and/or any consequent damages, howsoever caused, based on the use of this information.
Stabilant, Stabilant 22, and product type variations thereof are Trade Marks of D.W Electrochemicals Ltd.
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