"N_Cook" wrote in message
...
Jeff Liebermann wrote in message
...
On Tue, 9 Aug 2011 06:21:23 -0500, "Mark Zacharias"
wrote:

I see mechanical ones go bad ALL THE TIME.

I designed one into a marine radio and regretted it. If it moves, it
breaks. After about 10 years, all the encoders have probably been
replaced at least once. I also have a few ham radios (Icom IC-735)
with genuinely horrible mechanical shaft encoders, but that respond
well to cleaning.

... but it was said
that there was a pushbutton function on the OP's unit which the encoders
I
see don't have, but one of the pics previously posted look like some I
stock (and pay about 1.00 each for).

The CUI data sheet shows versions with a push button option.

They go bad from tarnished contacts, in
my opinion, but my friend Arfa opines that it is the migration of
silicon
lubricant that is the root of the problem.

In my never humble opinion, y'er both right. It's both tarnishing and
the silicon grease that causes problems.
http://en.wikipedia.org/wiki/Polydimethylsiloxane
It tends to absorb aromatic hydrocarbon solvents. It also tends to
have residual acetic acid used in the manufacture. Both are very mild
oxidizers that will eventually rot the surface of any metal contacts.
Once pitted, the contact area is reduced. Silicon grease enters the
voids, and since it's an insulator and incompressible, eventually
ruins the electrical connection. Using soft metals, such as PCB
copper, for contacts helps because the wiper scrapes away any surface
pitting. That only works until the copper is worn away. I've seen
encoders with grooves worn into the PCB traces.

In desperation, I found that cleaning off the grease from the copper
with alcohol, and tinning the copper PCB traces, actually works fairly
well. The problem was that when I lifted the soldering iron, there
would always be a small solder points left behind, resulting in
multiple bumps as the encoder rotated. I managed to file or press
down the points, but the bumps are still obvious. One of my radios
was repaired in this manner several years ago and is still functional
(although the bumps are irritating).





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


I don't know if its relevant with these encoders but a few times I've
found
with preset size pots that appear in audio mixers. The grease hardens and
then lifts the very feeble wipers of the pots. No track wear at all as the
wiper action is so slight , so why the grease ?



I think the silicon grease is there to provide the "feel" when you turn the
controls.

Mark Z.