Bronica S2A shutter won't fire reliably/aperture won't stop down

[markaudacity]

Hi y’all,

I just picked up an S2A that’s in very nice shape, minus the ubiquitous focus screen and mirror foam issues, but it has an annoying quirk. About 1 out of 10 shutter releases, the shutter won’t actually fire until the camera is thunked on the bottom or, occasionally, if the aperture stop-down button is pushed. The mirror always flips down and the screen blind rolls out, but the shutter itself doesn’t run and thus the mirror and blind don’t return to home position.

If the stopdown button is held while the shutter is tripped, it fails to fire much less frequently, I’d say 1 in 20 shutter trips. It will occasionally fire sluggishly with lens mounted and stopdown not held, IE, there will be a ~1/4 second delay during which it sounds like mechanisms are moving sluggishly, and then will lurch forward and the shutter fires. There have been no problems with mirror return or aperture re-opening when the shutter does fire

The shutter consistently fires when no lens is mounted. There is no discernible difference in failure rate with or without a loaded magazine mounted

So far, I’ve lubricated the stopdown linkage in the focus helicoid, both the lever that rides on a ring inside the bore and the sliding arc on the rear face of the helicoid. This seems to have improved the failure rate from the previous ~3/5 to the current ~1/10.

Has anyone else had this problem? It seems apparent to me that the nature of the problem is that the aperture mechanism can’t impart enough force to close the aperture against its return spring. I wondered if there’s an adjustment somewhere for the stroke of that mechanism. As I understand it, the action of the mirror falling seems to trigger the stopdown mechanism, so I had the thought that perhaps it’s not moving though its full travel, explaining the marginal performance rather than outright failure.

I understand that there are fewer and fewer folks willing to work on the mechanical Bronicas, but I’m pretty decent working with small mechanisms and clockwork—I got an Kiev-60’s double-exposure lockout functioning, for example—so I would like to at least try to fix this camera, especially since it appears to be in near-mint condition otherwise (excepting the foam, which I plan to fix today). I eagerly await any insight folks can offer, as I’m pretty excited about my first medium format system camera, particularly about the interchangeable backs.

 

[markaudacity]

Update for future Googlers: it seems like the tab in the helical that actuates the aperture lever on the lens is bent such that it can't reliably stop down the aperture. Since it is bent at an angle, I suspect the lens lever pushes the ring the tab is part of outward into the body of the helicoid, and the mechanism seems EXTREMELY sensitive to drag in that linkage. Even without a lens mounted to the helical, the drag in the linkage is sufficient to stop the shutter from firing some of the time. With the lens mounted, it fires reliably significantly less.

I believe the aperture actuation mechanism in the camera is functional. I put my finger in its path and fired the shutter, and it had no problem shoving my finger out of the way. I was surprised by this, since the drag on the helicoid's linkage is very slight when I actuate it manually, much less than the force I imagine it requires to push my finger out of the way.

My guess (and this is just a guess) is that the mechanism relies on momentum rather than straight-line force, and the drag in the linkage decelerates the actuator just enough that it can't finish its travel to the point where it trips the shutter. I haven't seen the entire gear train inside the camera, so I don't know if the aperture actuator trips the shutter or if there is another power path to the shutter release latch. When the stop-down button is pressed, it pushes the mechanism that last little bit that it isn't able to move on its own and fires the shutter.

Unfortunately, when trying to bend the tab back straight, I bent the ring a bit so it now drags when moved, so the problem is now worse. The silver lining is that this proves that the drag in the linkage is at least part of the problem.

 

[Sirius Glass]

I commend that you send it to a place that has repair facilities such as KEH.com for an estimate.

 

[reddesert]

The focus helical on the S2 / S2A / EC is a removable part, so if the camera body appears to be working ok, one option is to find another helical and try that.

Richard Haw has a rebuild of a S2 focus helical here: https://richardhaw.com/2017/09/24/repair-bronica-helicoids/ He actually separates the helical threaded parts, which I try to avoid doing at all costs with lenses/helicals, because I find it really hard to get those back together right. You probably don't need to mess with that. What I have done is: the inside of the helical is lined with a dark gray baffle/shroud in several pieces, fastened with screws. I took the baffles out and put them back on - can't recall exactly why, but they were loose or I wanted to get at the inside. IIRC, the aperture linkage moves between the baffles and the inner body of the helical. It is possible that your aperture actuating lever is hanging up in that space, and that carefully removing the baffles will allow you to inspect or rectify it.

 

[markaudacity]

The focus helical on the S2 / S2A / EC is a removable part, so if the camera body appears to be working ok, one option is to find another helical and try that.

That did it. Replacement helicoid eliminated the problem completely.

The aperture lever on this one is much beefier than the simple bent tab on the old one. It’s mentioned in the service manual, so this must have been a common issue.

Pictures to come for future Googlers.