I opened two trigger mechanisms: one was on a well-used Cheetah MKIV and the other was a never-fired Cheetah MKIII. The process is the same for both so I'll post pictures of the MKIII sequence here. Many thanks to
RISXC for describing the process originally.
First, you need to remove any pins holding the plastic dovetail rail insert to the main scope/sight mount. In this case there was one pin (arrowed):
Next, wind the elevation nut (blue arrow) all the way up by turning it counter clockwise. Note under the nut there is a plastic hook (yellow arrow) which is part of the dovetail insert and which must be moved rearward before it can be released:
You can now move the dovetail insert rearward and lift the rear up, just make sure you don't damage the coil spring whilst freeing up the insert:
With the insert removed you now have access to the knurled nut and the spring (arrowed). Remove the spring and then get a hex key for the grub screw in the center of the knurled nut.
Hold the nut tight with your left hand and loosen the grub screw with the hex key, remove the grub screw entirely.
You now need to slide the knurled nut out. It will only come out the right side, and it is a tight fit. In my case it would not come out unless I used a flat screwdriver to lever it out:
With the knurled nut out, you have access to the main screw holding the sight/scope mount onto the frame. Unscrew that (blue arrow):
Now you can remove the mount by lifting the front up (arrowed). The rear sits in a recess in the frame, take care not to damage the mount or the recess:
Continued...