Electronics question - climate control components

[bobins]

Brain picking time for all you electronics experts....

One of the climate control knobs in my X7 has started going intermittent - it's a common enough fault and will most likely affect all identical controls in the end. For the avoidance of doubt - it's this type of control :

Climate control

It's the driver's side one that's playing up, so that would indicate it's a wear and tear related problem as the passenger's side still works fine and that gets a lot less use. I decided to take mine apart to see what's inside - hey presto....

Underside of knob - own work

This (above) shows the underside of the control knob, the red circles show a castellated metal ring which turns with the knob.

Sensor - own work

This (above) shows what I assume to be a Hall sensor, though it may well be a light sensor. The castellated ring passes through the sensor when you turn it.

Would it make sense that it is a Hall Effect sensor, or is it more likely to be a light sensor ? Is there any other type of sensor it could be ? Are Hall sensors known to go intermittent or are they either in a working state or fubar'd - same question for light sensors ? Could it be the ring that's at fault ? Is there anything that can be done to make them good again ? Re-magnetise the ring ? - or is that barking up the wrong tree ?
Any ideas ??????

Is it worth hoarding all the spare climate control panels now so I've got a supply to last me another 10 years ?

[xantia_v6]

It is much more likely to be a light sensor, with quadrature detectors to sense the direction of rotation.

It is hard to see how such sensors (or even hall effect sensors) could suffer wear out, as they have no physical contact with a moving part.

Is there sideways pay in the control shaft?

[bobins]

Hadn't thought about play in the control shaft ! Difficult to quantify how much play though as there's a certain amount of slop on both control knobs, and it doesn't work however you hold the control The control is supposed to be bi-directional - and it's equally intermittent in both directions The previous time it went dodgy it wouldn't work from starting from cold from home, but would work once I restarted the engine after about 20 miles. This experience was repeated on the return journey. That could point to a voltage related issue... only the passenger side worked faultlessly

[GiveMeABreak]

In that second picture it looks like the metal is contacting that white contact strip at the top. Is it this that has anything to do with it and if so has it slackened slightly?

[xantia_v6]

If you have a working spare, you could try mating the mechanical half of one with the electronics half of the other, to localise the problem.

[bobins]

The contact strip at the top is a bit of sprung metal to act as a detent spring on the castellated section to give the control knob its 'notchy' feel as you turn it.

Good suggestion about swapping working bits (Xantia_V6) - I might invest in a second hand climate control section so I can do some testing.

[xf1ref]

In the third picture I think is the IR optical encoder. In the optical mouses are similar encoders at the scrolling wheel. Try first to see if there is a cold joint at the sensor or near pieces. If the control knob is ok I would suspect this sensor.