Lens diaphragm fixable?

I have this old Nikkor 50 1.4 that I've kept as a decorative piece on my desk for a while now. I tried cleaning it, something I have done before (over three years ago) and I must have loosed the wrong screw or messed something up because the diaphragm has become loose and unresposive to the levers. Now it's stuck, some of the blades are visible through the lens but the others seem stuck in the wide open position.

Is this something that can be repaired easily by a professional or have I damaged it too much?

The only way to find out what the problem is… Is to send/take the lens into Nikon ( or a Nikon authorized service center) and have them take a look at it.

That would definitely be a professional camera service job, preferbly Nikon themselves.

A repair like this may well be possible for the home engineer. You must be exceptionally careful with the disassembly job though.

If you're not confident with this job, you probably wuold be better send it off to a trained engineer.