On Dec 15, 4:28*am, "Arfa Daily" wrote:
"Dave Plowman (News)" wrote in ...

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

Arfa, what do you clean the encoder wheels with?