Konica UC Hexanon 45-100mm Aperture return issue

[Elaguapo]

Hi all,

Normally I just read posts but I'm stuck with this one!
I’m repairing a Konica UC Hexanon 45–100mm f/3.5 (Konica AR mount) and have an issue with the automatic aperture return mechanism.

The aperture blades respond correctly when the rear aperture actuating lever is moved by hand.
However, the lever does not return under spring tension.
After moving the lever to open the aperture, it stays stuck wide open.
I have to manually push the rear lever back with my finger to make the aperture stop back down to the selected setting (for example f/16).
There is zero snap-back or spring return.

Aperture blades themselves are free and do move.
Internal diaphragm is not seized.
The problem appears to be in the rear mount auto-diaphragm linkage, not the iris blades.
What I found after removing the rear bayonet:
Under the Konica AR mount there is:
a brass aperture return lever,
internal diaphragm follower,
I think I may be missing spring or catch.
The brass lever moves freely but has no preload/tension.

Does anyone have:
a repair manual,
a rear mount teardown photo,
or a clear picture showing where the aperture return spring attaches on this specific lens?
I’m specifically trying to determine:
whether the spring hooks from the brass return lever to a chassis anchor hole,
and what the correct spring orientation/path should be.
Any photos of the rear linkage under the bayonet mount would be hugely appreciated.[url=https://forum.mflenses.com/userpix/20265/big_12889_20260429_103745_1.jpg][img]https://forum.mflenses.com/userpix/20265/12889_20260429_103745_1.jpg[/img][/url]
[url=https://forum.mflenses.com/userpix/20265/big_12889_image1777455359695_1.jpg][img]https://forum.mflenses.com/userpix/20265/12889_image1777455359695_1.jpg[/img][/url]

[visualopsins]

Welcome Elaguapo! (Handsome one, eh? )

Somebody will be along short;y with help. You can upload pictures now if you like.

[stevemark]

I don't have much experience servicing Hexanons, but cincidentally today I cleaned (fogging / fungus) and re-lubed an AR 1.4/57mm, an AR 4/200mm and a Tokina RMC 3.5/35-105mm with Konica AR mount. So now I'm at least familiar with the basic construction of the lenses.

I have one of those (pretty rare) UC 3.5/45-100mm lenses, and if you post a few images of what exactly you are looking for, I may be able to help.

S

[Elaguapo]

[Elaguapo]

Thank you. I may be wrong but it looks like the brass lever should be attached to the white part on the image possibly by a spring or similar. It would be great to see what a working lens looks like to compare.

[stevemark]

[Elaguapo]

[quote="stevemark"][quote="Elaguapo"]Thank you. I may be wrong but it looks like the brass lever should be attached to the white part on the image possibly by a spring or similar. It would be great to see what a working lens looks like to compare.[/quote]

Ah yes, that part looks [i]exactly [/i]the same as e. g. in an AR 1.4/57mm which I had opened yesterday.

The center of the spring (the round part) spring is attached to the large brass screw, whereas its two ends should push the two other "knobs" (the steel screw and the the brass knob) apart from each other.

S[/quote] thanks for the information. I may be able to source a damaged lens as a donor. I dont suppose you have any images. It would be great if one of their cheaper lenses used the same part.

[stevemark]

[Elaguapo]

Thank you so much really appreciated

[stevemark]