Replaced rotary encoder weird behaviour - Page 1
Forum section: electronics / repair

author: VanitarNordic
author_rank: Frequent Contributor
timestamp: April 16, 2018, 07:38:33 pm
content: Hello,I have an OWON SDS7102 oscilloscope which one of the knobs was not functioning properly.I replaced the faulty rotary encoder with a new one and the problem was solved, but I don't know why it works in reverse. it does not make a problem, but I'm curious why the direction has changedfor example turning the knob to the right was increasing the value, but now it decreases it.

author: Samogon
author_rank: Frequent Contributor
timestamp: April 16, 2018, 08:18:36 pm
content: Phase angle if not correct try to swap A and B outputs

author: VanitarNordic
author_rank: Frequent Contributor
timestamp: April 16, 2018, 08:31:39 pm
content: Quote from: Samogon on April 16, 2018, 08:18:36 pmI just bought a new encoder with the same size and characteristics and replaced it. I saw no information about the phase angle, if it could be different in rotary encoders. I can not damage the PCB for this.

author: Samogon
author_rank: Frequent Contributor
timestamp: April 16, 2018, 08:44:41 pm
content: Are you sure that encoders exactly match? If yes then software is reading it wrong.

author: VanitarNordic
author_rank: Frequent Contributor
timestamp: April 16, 2018, 08:59:25 pm
content: Quote from: Samogon on April 16, 2018, 08:44:41 pmThe only thing which I found is different is Detent. in the new one, the Detent, or the number of clicks in 360 degrees rotation is higher, but this should not make a difference in the direction change or make it reverse. it is just number of clicks.The software has no problem because it was Okay with the old encoder.

author: jmelson
author_rank: Super Contributor
timestamp: April 16, 2018, 09:03:36 pm
content: the replacement encoder has the opposite phase relationship of the A vs. B signals. So, for instance, on the old one, A would LEAD B when turned CW. Now, the new one has A lagging B when turned CW. If you rewire the connector so that the A and B wires are exchanged, the knob will work in the expected direction.Jon

author: VanitarNordic
author_rank: Frequent Contributor
timestamp: April 16, 2018, 09:07:43 pm
content: Quote from: jmelson on April 16, 2018, 09:03:36 pmHow can I be sure about this parameter when I buy them? I mean what term is used for this in the datasheet and so on? or if it is not written and the encoder is Unknown, then how can I realize what type it is.

author: jmelson
author_rank: Super Contributor
timestamp: April 16, 2018, 09:29:29 pm
content: I have no idea. The manufacturer should state something like A leads B for CW rotation, or often they give a logic drawing that shows the relationship of A and B signals.There really is no standard way to describe it.Jon

author: SL4P
author_rank: Super Contributor
timestamp: April 17, 2018, 05:39:37 pm
content: The bottom line is that the replacement part is NOT an exact exchange.Maybe it looks similar, or has. ‘B’ suffix (or some other indication that it’s a variant of the basic model).Your easiest fix is to get the EXACT replacement part.

author: VanitarNordic
author_rank: Frequent Contributor
timestamp: April 17, 2018, 07:08:25 pm
content: Quote from: SL4P on April 17, 2018, 05:39:37 pmThe problem is that the existing part does not have any identifications like chips, resistors, .... and so on and the only things that could be matched are size and detent number

author: Samogon
author_rank: Frequent Contributor
timestamp: April 17, 2018, 07:33:04 pm
content: Then reroute output connectors by cutting leads and making crossover connection with wires.

author: Peabody
author_rank: Super Contributor
timestamp: April 17, 2018, 09:04:36 pm
content: If you still have it, you might try taking the faulty encoder apart and cleaning it, and perhaps bending the internal contact arms so they press more firmly against the conductive disk. That actually works most of the time.Or, you might post a link to the replacement you used. Perhaps someone will know how to find the inverse of that one.You need to be careful that you get the right replacement. It isn't just the number of detents that may be different, which as you say doesn't really matter. But some encoders have the same number of pulses per revolution as detents per revolution. They go through a complete cycle of both switches between detents, and both switches are always open at a detent. The other kind has half as many pulses as detents per revolution. At each detent, both switches may be open, or both may be closed. They go through a half-cycle between detents.If the software expects the first type, but you install the second type, you will have to turn through two detents to get one tick recognized. In the opposite case, you'll get two ticks per detent. Better to get the type your software is expecting. It looks like you got that part right, or you would have noticed even more strange behavior.

author: MF-jockey
author_rank: Regular Contributor
timestamp: February 23, 2021, 05:42:36 pm
content: There is another way to repair the encoders by adding capacitors:https://www.eevblog.com/forum/testgear/owon-sds7102v-problem-with-encoders/msg3479200/#msg3479200It took me about 1 hour.