Dana Mon, 1 Mar 2021 04:37:29 -0000 (UTC), bob prohaska 
napis'o:
> Martin Gregorie  wrote:
>> On Sun, 28 Feb 2021 19:29:00 +0000, bob prohaska wrote:
>>
>>> For some time  I lived with a an erratic scroll wheel on a Pi4.
>>> Anybody got a hint what might be going on? I can understand a USB hub
>>> not working right, but it's much harder to understand how it could work
>>> right for pointing and wrong for scrolling.
>>>
>>> The mouse and keyboard are both elderly Dell take-offs from scrapped
>>> computers. The keyboard is model sk-8125, the mouse is model mo56uo.
>>>
>>> Thanks for reading, and insights appreciated.
>>>
>> I had the same problem recently with a Logitech M105 mouse: scroll wheel
>> was erratic, but clickers and optical tracking were fine. The problem
>> turned out to be a mouse full of hair and dust that interfered with the
>> optical sensors on the scroll wheel. Taking it apart, there's one screw
>> that holds the Logitech together, cleaning out the collected gunge inside
>> it and reassembly fixed it completely.
>>
>> I've had consistently good experiences with the Logitech mice: its been
>> my goto brand fir at least a decade.
>>
>> Or, there are plenty of that model mo56uo Dell mice on eBay for around
>> $US 8
>>
>
> After reading the replies to this thread I decided to try putting
> the USB cable for the mouse back into the hub port on the keyboard.
> It was meant to be a null experiment, replicating the original problem.
>
> To my utter surprise, the mouse scrollwheel seems to work perfectly.
> It looks as if the solution was merely to re-seat the connector.
> Evidently it was some sort of bad connection, much to my astonishment.
>
> Thanks to all for reading and replying!

Probably oxidation on the connector. Either or both.
Plug it in and out dozen times. That should "clean" it a bit.

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