The FED 1g is the last in a long line of Barnack-style Leica copies produced in the Soviet Union. Mine, according to the serial number, was produced in 1955. I haven't used the camera in quite a while because of a maladjusted shutter which caused a dark line to appear along one edge of the negative.
The explanation of the problem is that the second of the two cloth curtains in the shutter is under too much tension and it catches up to the first curtain a little too soon after the shutter is tripped. The solution to the problem is to slightly decrease the tension on the second curtain. The picture below shows the two little knobs with a screw in the middle of each which allow the adjustment of the tension on the two curtains. The one closest to the lens controls the second curtain. There are several places on the net where you can get instructions for making the adjustment. I used the one at rangefinderforum which can be found in the Russian FSU RF forum.
Truth be told, the instructions are pretty opaque. I removed the little locking screw while holding onto the big round nut with some pliers and keeping the tip of my screwdriver planted in the central screw head. The whole thing rotated a bit on its own, so when it got to about 180 deg. from the starting point, I returned the nut to its original position by twisting counterclockwise and put the locking screw back in place. I'm still not sure if what I did corresponded to the intent of the instructions, but I don't see any dark line as before in the negs, so I guess the problem is fixed. Below are a couple full neg scans from the roll I put through the camera following the repair.
There are a couple other common problems with these cameras. The film cassette tends to ride a little high in the chamber because of a slight difference between modern film canisters and the reusable metal one the Russians used. There is a little extra black light seal material in the modern cassettes which protrudes at the ends. That can be cut off to allow the cassette to seat better. If that doesn't do it, you can lay a penny on top of the cassette before you replace the back.
The other common issue is pinholes in the rubberized cloth shutter curtains. Provided the deterioration is not too advanced, you can fix that problem with a light application of black fabric paint which you can get at any crafts store.
In addition to the FED 50mm collapsible lens I have a 35mm Jupiter 12 and the corresponding wide-angle accessory finder. Both lenses are of excellent quality and I'm pleased to once again have an opportunity to put them to use.