I was having troubles with the projector just spinning without stopping at each slide. The finger that slips in and stops the turntable is linked up to pivot just below the blue wire in the center of the picture. It is driven open (so the turntable can spin) by the solenoid (bronze colored, just to the right) and restrained by the spring (between the pivot and the solenoid).

I (incorrectly) thought that if I could just make the spring stiffer, the finger would pull back in and stop the turntable. I tried to stretch the spring by loosening the left-hand screw in the foreground and pulling the lever towards me. WRONG! That screw is tied into the whole mechanism of the finger and will mess things up if you change it. Fortunately I remembered about where it was originally and it only took about three attempts to get back to the right place.

If you do loosen that screw, use a wrench, not a hex driver. I used a hex driver and wound up bending slightly the nearer blade on the microswitch. I had to take it out, straighten the blades so they were parallel and put it back in, before trying to figure out the right spot for the screw.

The pot to control the turntable speed is the round object on the right. If you adjust it with the power on, be very sure to use a non-conductive object to turn it. I might have tried that if I had needed to.