Olympus XA update
Do you see that little lever to the left of the camera lens? That's the f-stop lever, the one that was stuck halfway through its range.
In order to get to it, the sliding dust cover must be removed. Once it's off, it's time to search for the tiny roller that clicks to hold it in place. This is best performed by a wizard, someone skilled in crawling about in the dark while muttering incantations. After the pesky little bugger is found, it's a simple matter to remove the top, bottom, and right side of the camera. Well, it would be a simple matter if it weren't for a couple of screws that really didn't have to be removed. And then there's the minor problem of a couple of hidden screws as well.
Let's just say I had a good time with this puzzle.
As it turned out, the f-stop lever was stuck because it was ever so slightly bent. That part on the left (ZK739700) has the detents for the f-stops and it's guided in its up and down travel by a pair of small shoulder screws. The fork on its right side engages a small pin on the aperture assembly. The adjustment handle on the part had been forced upward, bending the upper slot inward very slightly. The bend wouldn't go past the shoulder screw.
I found this by removing it from the camera and working the aperture pin up and down. It traveled freely, so the problem had to be in the linkage. The bend was so slight I missed it the first time, thinking that it was hitting the camera body at the upper end of its travel. Wrong. Careful examination revealed the pinched slot. The part is just mild steel so I bent it back outward with the fat end of my heavy assembly tweezers.
While I had the camera apart, I did a quick cleaning on the rangefinder assembly. It looks better, but clearances are so tight I couldn't get a cotton swab onto some parts of it. I'll do it again sometime soon and I may try a pipe cleaner or a wad of cotton held in a pair of mosquito forceps. One thing's for sure - I won't disassemble the rangefinder!
The XA is interesting because it's so tiny. Everything has to be aligned just so. The other cameras I've had apart - the Canonet and the Yashica Electro - are more like big American cars with tailfins by comparison.