Washing machine main control knob. Is it a rotary encoder? - Page 1
Forum section: electronics / repair

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 21, 2024, 05:32:02 pm
content: My Hoover washing machine has failed a few times with no display and no action at all. Turning the mains off and on again has returned it to life. Today it failed again mid cycle so I removed the control board PCB and examined it carefully for obvious issues and dry joints / failed joints. All seemed good.I put it back together agin and now, by CAREFULLY fiddling with the main control rotary knob that has 15 positions including the off position it once again came back to life. The two wire cable and two pin connectors are sound, low resistance and making good contact with the control board PCB and the tiny PCB of the control that I am assuming IS an encoder.However mid cycle once again the display disappeared and it stopped. No coaxing it back to life at all now... The main knob has what looks like it may be a rotary encoder, with detents, but I think the detents are mechanical and external to the encoder itself. in a plastic housing that the encoder is held on to.surprisingly to me, only two of the three pins on the encoder are used. How might this work? Is it likely to be a rotary encoder or something else, and is there a way to safely fool the control board to "do something -- anything in fact to prove this rotary device is the culprit? I will Google rotary encoders, but a brief look shows most have at least five contacts....Thanks and a very happy Christmas and a healthy and prosperous New Year to all members.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 21, 2024, 06:27:28 pm
content: well photos would help, some bands are using the pcb as the encoder traces, and only dial contacts goes over the traces, and yes some have real encoderswith real encoder or elseyou have examples on the web or youtube videos who explain the 3 pins detection, forward or reverse .... on how an mcu detect the rotationSome encoders have : say 12 detents and other have 24 detents etc .. and some called enter press in pushing the center shaft witch is the 2 supplemental pins for a 5 pins total count, some have more ...and maybe you're dealing with customized one too ? the dial could be ok and your problem(s) could be mcu, supply issues etc ...

author: ebastler
author_rank: Super Contributor
timestamp: December 21, 2024, 06:38:44 pm
content: Without photos and/or the exact model number of your machine, this amounts to crystal-ball gazing.A standard (cheap) encoder seems unlikely since it would only be able to detect relative movements of the knob, not its absolute position. And a two-pin cable seems unlikely too. What does it connect to? A PCB with just the "encoder" on it? Are there additional power supply connections? Are the displays on a separate circuit board?

author: Gyro
author_rank: Super Contributor
timestamp: December 21, 2024, 07:02:02 pm
content: The only type of absolute position control knob I can think of that has only 2 pins would be a resistive one. In repair terms, hopefully this would be in the form of PCB segments, a wiper and smd resistors, rather than a printed resistive track.With the appropriate complimentary resistor and ADC input on the controller PCB, this would provide sufficient resolution for a reasonable number of fixed positions. This method used to be used fairly extensively for the buttons on things like VCRs. Maybe it still is.Agreed, photos are needed to confirm what is going on and avoid confusion.

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 21, 2024, 07:21:14 pm
content: Thanks for the replies, as my wife is panicking and seems to have forgotten that we did not all go around in filthy clothes before the invention of the washing machine I have ordered a new "switch". Agitating washing in a sink seems total anathema to herHowever I am nonetheless keen to understand how this thing works with just two wires to the controller board PCB which is all surface mount. Both the controller board PCB and the switch have fingers for three wires, only two (the outermost ones) are used.Here's a link to the rotary control itself. Thanks again.https://www.espares.co.uk/product/es1802455?utm_source=google+shopping&utm_medium=shopping&utm_campaign=google+shopping&gad_source=1&gclid=CjwKCAiA65m7BhAwEiwAAgu4JDV9ZXfPC4x0E9MSFZffmX0MRbi4Nlo2ZpOQ1izYLcEWGo_WiV1PYhoCwIwQAvD_BwE

author: Gyro
author_rank: Super Contributor
timestamp: December 21, 2024, 08:01:08 pm
content: Yes, it looks resistive to me. You ought to be able to check it out with a dmm - you might even be able to find a point where it goes open circuit. It looks as if the board can be unclipped, hopefully without losing the tabs.At least the replacement isn't silly money!

author: ebastler
author_rank: Super Contributor
timestamp: December 21, 2024, 08:32:22 pm
content: Here's the manufacturer's excuse for a datasheet:https://www.rold.com/wp-content/uploads/2022/03/RD_Encoder.pdfNot much info at all, but they call the technology "Analogic". So yes, it looks like just a cascade of resistors. Should be feasible to open, measure and repair it?

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 21, 2024, 09:34:00 pm
content: OK, thanks a lot again, I'll have a play with it and compare it with the new one. If it's open circuit I guess it's knackered.