CAB-2 voltage drop turning knob clockwise???

Sounds like a problem with the CAB2 encoder wheel.

Is one of you buttons stuck? Say a Aux1 or function 0 ?

This is an issue I've had with various Cab-2, only it worked the other way, I'll turn the locomotive speed all the way down and then all of a sudden it's speeding up.  Like John says, it's an issue with the encoder in the Cab-2.

Sinclair, yes, I have had the same reverse effect. It actually works in both directions. Sometimes when you turn counterclockwise, you will hit a zone where the voltage increase slightly instead of decreasing. 

It occurs exactly once each revolution of the velocity throttle knob. I thought it was the tach tape inside the CAB-2, so I took it apart, inspected and cleaned it. Still no improvement. It is a software issue apparently.

I really doubt it's a software issue or we'd all be seeing it.

Problem solved. Sharp metal edges of optical sensor were scraping at the inside surface of the plastic tach wheel. Small almost impossible to see burrs of plastic were getting shaved into the apertures of the wheel interfering with the optic sensor. I'm surprised more people aren't seeing this issue. This was my first tear down and rebuild of a CAB-2. Frustrating to repair, kind of  like a PlayStation remote which has parts that spring all over and requires ten attempts to reassemble. 

Nice catch.  I'm surprised you didn't feel the contact as it rotated. 

Told you it wasn't software.

Yep, you were right

But can you explain how that optical tach wheel knows whether it's being turned clockwise or counterclockwise? I can't figure it out despite being an engineer. 

On a locomotive, a tach wheel only records speed. 

There are two optical sensors, and their phase tells you which way the shaft is turning.  Let me find a better explanation...

Here's a pretty good page on how they work: Rotary Encoders – Understanding for Practical Implementation

Thanks so much. Great description of the rotary encoder concept. Now I understand exactly why the slight  damage to the disk caused a scrambling of the signal sequence which confused the rotation direction. Fascinating. 

I like it when there's a site that does all the typing and doesn't require me to do it.  

I was trying to figure out a way to do something like that on a motor encoder so I could determine the direction of travel, but the size of the stripes and positioning of the dual sensor is pretty critical.  I figured it would be a problem to have any sort of repeatability between installations.

Reviving this thread after searching cause I'm "bran new" to Legacy n cab2 remote. Less than an hour operation, in fact.  Same problem as previously stated in that red knob causes sporatic up/down voltage as knob is turned in the same direction. Worked great out of the box, then started acting up. Before I screw this up, how does the knob come off to check for these "shavings" or some other problem?  Anything else might be causing this problem? Thx in advance for any help. TW