Does anyone have a diagram or explanation of how the internals of a vernier throttle work?

Once in a while, when testing the prop control on my plane during runup, I pull it out and get no change. When this happens, it seems to pull back easier.
When the plane was in for it's annual recently I had it looked at but everything seemed to be working fine. During flight, I only ever twist the control and never have any issues. So I'm wondering if it's somehow the control knob itself. But I don't really understand how the mechanics of being able to directly pull the control, or twist for fine adjustments works. My theory is that whatever the mechanism is somehow slips in these occasions when I pull the control.