Flaky "data encoders"

[Hamad bin Turki Salami]

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

 

[Arfa Daily]

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

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