Hi All,

Appreciate any advice. I needed to relocate a rotary encoder from the main PCB via a ribbon cable approx 12" long. See images below - original with encoder on the PCB, and subsequent on the ribbon cable fly lead. The encoder no longer works - it controls volume on a car radio, and the volume now jigs and jogs up and down no matter which direction I turn the encoder. I've double checked the wiring with a meter and can't see any issue or shorts. The push button function on the encoder works fine.




Any advice on how to fix this?

Thanks,

Earlysport.

 

If that is actually an encoder it appears to be rather delicate construction, and so the removal process may have damaged it. That sort of encoder alternately makes contact between one moving contact and alternates connection to one of two conductive tracks. There is usually a bit of overlap.
A replacement encoder with a more durable construction may be the solution.

 

Welcome to AAC.

Your photos are too small and low resolution to make out the connections to the encoder. The first place I would check would be those connections—that the solder joints are good and with no bridges, and they pins correspond to the correct places on the PCB.

 

Thanks for the input guys. I have triple checked and measured the connections. I wondered if the length of ribbon cable could cause an issue , but it seems not.

It does seem likely the encoder has an issue, so I've ordered some replacements to try substituting. I didn't use much heat when removing it from the board, but I guess you never know.

Thanks.

 

Inside the encoders I've messed with are simply switches. Switch A and switch B. When rotated one direction A closes before B. After B has closed A opens. This is essentially two square waves that overlap each other. Depending on the direction of rotation AB going one way and BA going the other, tells some electronics some input from a user.

Switches get dirty and can become problematic. You might try cleaning the switch with some contact cleaner. Other encoders may have power and ground associated with A & B. If either of those lines are not functioning properly that can introduce error.

I'm with Ya'akov on this.

The first place I would check would be those connections—that the solder joints are good and with no bridges

A bad solder joint can be difficult to find. Sometimes you can see a fracture other times you can't. Having worked Post Failure Analysis on many circuit boards, I've seen excessive heating and reheating of solder joints cause fractures with internal connections. Without destructive analysis you are not going to find it. OR it could simply be a cold solder joint. You might probe it with a meter but the act of probing may fool the test.

My recommendation is two fold: First, check each wire for solder wicking under the insulation. If solder has wicked it could cause the wire to fracture, resulting in an intermittent open circuit. And since switches open and close - an uncontrolled open signal can cause uncommanded changes. The other thing I'd do is add flux and then reflow all the solder joints. If I've found that all the wires are for sure in good condition, no wicking or fracturing then soldering may be the next best alternative.

Countless times I've seen people refer to an electrical issue as a "short". That's only half of it. The other half is "open". Not all electrical failures are "shorts". Just because someone reports an issue as a short doesn't necessarily mean I believe it to be a short. A short is an unwanted connection. If something was shorted then it shouldn't function at all. You're experiencing erratic functioning.

Lastly:

and the pins correspond to the correct places on the PCB.

Many times I've seen mis-wiring issues. Guilty of that myself. Double check the wiring. Make sure everything is right.

 

Inside the encoders I've messed with are simply switches. Switch A and switch B. When rotated one direction A closes before B. After B has closed A opens. This is essentially two square waves that overlap each other. Depending on the direction of rotation AB going one way and BA going the other, tells some electronics some input from a user.

AKA quadrature encoder, due to the 90° difference between A&B with A used to tell rate of change & B the direction.

 

I have experienced some contact bounce with that type of encoder. That might be causing your problem.

 

I have experienced some contact bounce with that type of encoder. That might be causing your problem.

If it's properly decoded, contact bounce should cause a problem with a quadrature decoder -- that's the primary reason for it producing quadrature signals. They should be able to bounce as much as they want as long as they are done bouncing before you get to an edge of the adjacent track. Or are you saying that you've had them bouncing at arbitrary locations even well away from the track edges?

 

If it's properly decoded, contact bounce should cause a problem with a quadrature decoder -- that's the primary reason for it producing quadrature signals. They should be able to bounce as much as they want as long as they are done bouncing before you get to an edge of the adjacent track. Or are you saying that you've had them bouncing at arbitrary locations even well away from the track edges?

I did have to take the bounce into account when I wrote the program to read it. Unfortunately, the TS does not have that ability. That is why I mentioned it.

 

I have experienced some contact bounce with that type of encoder.

Good point. I didn't even think of that.

Just an opinion, I would think the contacts should stop bouncing before the second switch closed. But now I'm considering having A stable and B bouncing. But that wouldn't account for reacting in both directions. Still, bounce is a good thing to take into consideration.

The type of encoder I like better is a photo optic encoder. Slots and LED's with photo transistors to act as switches. No bouncing there.

 

The type of encoder I like better is a photo optic encoder. Slots and LED's with photo transistors to act as switches. No bouncing there.

Also capable of many thousand's of counts/rev.

 

It may also be that the connection between the encoder lugs and the printed pattern for the encoder traces has become intermittent. That can happen if it is wiggled at all while unsoldering from it's original location. That also happens with some kinds of potentiometers as well. quite a source of aggravation.
And certaiinly contact cleaner or control cleaner might solve the problem.