Flaky "data encoders"

There's a simple component that frequently gets flaky on a certain kind of synthesizer I use. The component is called a "data encoder." Its something attached to a knob that you turn to scroll through lists. It looks like a pot, but it's not a pot. It has three leads, which I'll call left, middle, and right. As you turn the knob, the middle lead connects to the left lead, then disconnects, then connects to the right lead, then disconnects, and so on.

The connections have a rhythm: ... Left (short pause) Right (long pause) Left (short pause) ... Thus, the device knows which way the knob is turning and how fast.

This kind of component quite frequently becomes flaky, in that scrolling is erratic, sometimes making big jumps, or moving in the wrong direction, or getting stuck without moving either way. I think this happens because the connections are not always being made on the left or the right or either side, so the synthesizer gets confused about which way and how fast the knob is turning.

I can buy replacements for these things, but they're not that cheap, and replacing them involves a fair bit of work, opening the synth, desoldering 5 or 9 joins, and soldering in the replacement.

Now, it turns out that I can get easy access to these data encoders without even opening the synths. Furthermore, I can open them up to get at their innards without any trouble. There's a top part with a disk attached to the post for the knob that turns with the knob. It has copper strips going out radially from the center like spokes. On the bottom, it has three copper brushes which are connected to the left, middle, and right leads. As the disk turns, its copper strips alternately make connections between the brushes in the way described above. The whole inside is full of some kind of grease.

It seems to me that it shouldn't be hard to fix these things. Perhaps I just need to clean the brushes and copper strips so they make better contact, then replace the grease.

Questions:

Do people here agree it's probably simply a problem with leads needing to be cleaned?
What's the best way to clean the brushes and strips?
What kind of grease do I put in such a component?

"Hamad bin Turki Salami" wrote in message news: snipped-for-privacy@Spam.aol.hotnet.ibm.net...

This is a very common problem on Hi Fi's - particularly most models of Aiwa - and I fix them all the time. The problem is caused by the grease that you mention, migrating down into the chamber where the encoder disc and contacts are. If you use isopropyl alcohol on a cotton bud ( Q-Tip ), the grease will turn into something like a stringy rubber, which is then very easy to remove with fine tipped tweezers. Once the bulk is off, you can continue with the isopropyl alcohol, until the disc is completely clean, dry and grease free. Likewise, the contact fingers, but be careful of these. They are quite delicate, and their relative positions must not be moved.

You will find that there is still plenty enough grease up in the shaft bearing to get the 'stirring treacle' feel when you rotate it. I usually finish off with a small amount of good quality switch cleaner / lubricant in the contact chamber before reassembly. I have done many many of these over the years, and have never had one come bouncing back. I think that what the encoder generates is called Gray code. Basically, the encoder produces a pair of pulse trains, offset from one another, phase-wise. The decoder electronics then looks at this relative phase difference, and depending which pulse train is lagging or leading the other, can determine which direction the encoder is being rotated. Checking the pulse rate determines how fast the encoder is being turned for quick skips or slow detail tracking through menus, or whatever the encoder is controlling.

Arfa