"Arfa Daily" wrote in message
...

"Dave Plowman (News)" wrote in message
...
In article ,
Mark D. Zacharias wrote:
Nah, it's the encoder. I've taken them apart. The contacts are
tarnished.

Crikey - thought the whole idea of a shaft encoder was to get rid of any
mechanical contacts. I assumed they were all optical etc devices.

--

The one that's commonly found in many hifis Dave, comprises a printed
circuit disc with broken rings of (gold plated?) print on it. This is
attached to the shaft. The plastic body of the encoder has a set of
contacts on it which I think are also gold plated. The whole thing puts
out Gray code or some such, that can be used to derive a rate and
direction of rotation. The system control micro then looks after turning
this into an I2C data stream to work the digital pot IC for volume
control, and the display decoder so that it can put up a pseudo dB
display. The useful thing about using such an encoder, is that it can be
used to control other functions too, such as tone and radio tuning and so
on. It's also cheap compared to optical devices.

As far as problems with them go, I don't think it is so much that they are
unreliable by design, more that their problems have been caused by the
manufacturers being a bit enthusiastic about giving them a high-end 'feel'
in use. To give them this 'stirring treacle' feel, they fill the shaft
with some kilopoise type grease, and this seems to migrate down onto the
disc and contacts, where it wreaks havoc with the operation. Once it has
been carefully cleaned off chemically, the contacts and disc are usually
bright shiny clean, as you would expect gold-plated contacts to be. I
usually finish off before reassembly and refitting, with a small drop of
cleaner/lubricant on the disc. They always work perfectly after this
treatment, and I can't remember ever having had one fail to be recovered.

Arfa



I've had one or two that didn't clean quite so well. One was on a JVC shelf
system which caused a BUNCH of extra labor to re-do, which involved
replacement rather than cleaning the second time around. I wasn't going to
risk another re-do.

BTW I don't think it's grease migration. I think it's silver content in the
switch tarnishing like a VCR mode switch. A good cleaning with De-Oxit and a
fiberglass nick-sander brush usually gets it but the parts are actually
pretty cheap, and there's only a couple types in common use. I get them from
Onkyo.

Mark Z.