I have a Fotodiox PK/AF-PQ adapter (with the 'pod shoe and aperture control ring) which had a stuck adapter control ring. On close inspection the adapter ring was noted to be cocked and the ball bearing in the detente notch sector was visible.
Loosening and re-tightening the three screws in the face of the mount allowed the ring to re-seat properly. Note: a JIS cross point driver is called for here. If not available, try a very narrow straight slot driver.
The larger straight slot screw in the ring is not a factor; it merely positions the ring in a slot in the barrel. (Replacing it with a longer screw might allow the control ring to be locked at a given position. I didn't try that.)
| 
Similar Threads 
