Dodgy hall effect input on microwave controls.

[Zog]

I haven't actually taken it apart yet so I am assuming it's a hall effect device.
When the microwave was new it was very precise and could adjust it with ease.

Now when I turn it it just jumps around all over the place. Sometimes advancing a minute like it's supposed to sometimes 10mins.
I have noticed this happening on a few devices over the years. My car radio springs to mind. Similar problems.

What on earth could cause this ? Maybe it's optical ?
Optical would not be common in consumer electronics would it ?

[Ian.M]

Probably a worn out mechanical rotary encoder.  Once enough of the contact fingers wear away, they typically become so intermittent that the debouncing can no longer cope and the direction of movement can no longer be reliably determined.  If it is a mechanical encoder, its not too far gone, and you can get the encoder open without FUBARing it, then a thorough cleanout, retensioning the contact fingers and applying a good quality contact lubricant may get a bit more life out of it.

[Zog]

Mechanical encoder. Didn't think of that. Would explain a lot.
Why on earth put something like that in for gods sake.
Typical of consumer electronics ?
Cheers.

[TheMG]

Yep, cause it's cheaper.

A shot of contact cleaner usually does the trick with those mechanical encoders, provided it's not completely wore out.