Prontor-S Delayed Action Weirdness

westopher · May 27, 2021

I recently overhauled* a Prontor-S shutter, and it's working well. BUT... When the delayed action (self-timer) is activated, the shutter blades open slightly while the escapement runs down, then the shutter releases normally and closes normally. It did this before the overhaul, and I was hoping a teardown would address it — alas, it did not. My guess is that it's actually something about the cocking and release, not the delayed action itself, but I don't see anything like this in the service manual, and after literally two hours of study and tinkering, I cannot figure-out what's amiss.

Any ideas? Thanks in advance.

* For the record, "overhaul" meant removing and cleaning both escapements, separating the halves, cleaning the blades and drive ring, and putting it back together. I did NOT remove the cocking lever, main spring, etc.

BrianShaw · May 27, 2021

In a synchro-Compur that is a normal behavior. I’d assume also for your Prontor.

westopher · May 27, 2021

BrianShaw said:
In a synchro-Compur that is a normal behavior. I’d assume also for your Prontor.

To be more clear, the shutter opens a roughly 2mm diameter hole straight to the film.

BrianShaw · May 27, 2021

Oh... it shouldn’t open that far. Normally the “preset” when self-timer is released is noticeable but never enough to expose film.

if it was mine I’d either remove the self-timer altogether or simply never use it. While they are nice features they tend to be more fickle than they are worth.

westopher · May 27, 2021

BrianShaw said:
If it was mine I’d either remove the self-timer altogether or simply never use it. While they are nice features they tend to be more fickle than they are worth.

Totally. And to be honest, that's the current course, as I put the thing back in the camera. It just bugs me when something that's "supposed" to work, doesn't. If it's a common issue with an easy fix and I can find the answer? I'll definitely address it. But to be honest, it's nice to simply have the retard escapement running perfectly; the rest is gravy.

shutterfinger · May 27, 2021

I have a #0? S and the blades stay closed, do not move until the timer runs down.
I suspect wear or improperly installed blades, cocking, or release.
(want it?)

westopher · May 27, 2021

shutterfinger said:
I have a #0? S and the blades stay closed, do not move until the timer runs down.
I suspect wear or improperly installed blades, cocking, or release.
(want it?)

Well, the blades are correct; normal operation is fine. It's the drive ring itself is shifting out of position when the timer starts. Like I said in the original post, I didn't disassemble the cocking lever, main spring, etc. as it's generally not needed to service them, but something's clearly not right there. I don't have a working original to compare against, which might help. By "want it," do you have a working one you're looking to get rid of?

Mamiya_Repair · May 27, 2021

On the Prontor-S, when using the delayed action, the blade operating ring is released immediately but a tab on the ring contacts the delayed action first gear segment and prevents the blades from opening until the timer runs down. You should be able to see this tab sliding along the delayed action escapement segment until a slot appears and the blades can open. Also, there is a spring located under the speeds escapement putting light tension on the blade ring to keep the shutter blades closed until the main spring opens them.

westopher · May 27, 2021

Mamiya_Repair said:
On the Prontor-S, when using the delayed action, the blade operating ring is released immediately but a tab on the ring contacts the delayed action first gear segment and prevents the blades from opening until the timer runs down. You should be able to see this tab sliding along the delayed action escapement segment until a slot appears and the blades can open. Also, there is a spring located under the speeds escapement putting light tension on the blade ring to keep the shutter blades closed until the main spring opens them.

Very helpful. I'll take a closer look. The spring under the speeds / retard escapement is intact and working; it must be something with the tab you mentioned. Appreciate the response!

Mamiya_Repair · May 27, 2021

The clearance between the blade opening ring and the ST segment should be very small, otherwise if it moves much, the blades will open a bit...

shutterfinger · May 27, 2021

westopher said:
By "want it," do you have a working one you're looking to get rid of?

I can't get the speeds to work correctly but all else is good. 250th is next to B on the right side of the speed dial. There are several variations.

albada · May 28, 2021

Mamiya_Repair said:
The clearance between the blade opening ring and the ST segment should be very small, otherwise if it moves much, the blades will open a bit...

It's likely that the tab on the blade opening ring is bent, allowing the ring to move too far before it touches the ST. At some point, somebody probably forced the shutter when the ST was tensioned, bending the tab. Bending the tab back will fix the problem.

unwantedfocus · May 28, 2021

This is the position of the blades when the shutter is cocked with the self timer.

This is the position of the blades when I release the shutter

The blades do open for a bit but there should not be a 2mm hole I think. I also attached a video hope that helps you somehow.

VIDEO

shutterfinger · May 28, 2021

My Prontor S uncocked

Self timer set, shutter cocked No blade movement!

Self timer set, 0 clearance between self timer block and blade controller tab.

Self timer not set, blade controller tab has about .010 inch overlap of the self timer set/lockout, a potential problem, should be .0001 to .001 inch clearance.

BrianShaw · May 28, 2021

unwantedfocus said:
This is the position of the blades when I release the shutter

This is exactly what I was relating in post #2.

westopher · Jun 3, 2021

albada said:
It's likely that the tab on the blade opening ring is bent, allowing the ring to move too far before it touches the ST. At some point, somebody probably forced the shutter when the ST was tensioned, bending the tab. Bending the tab back will fix the problem.

Thanks for additional info!

westopher · Jun 3, 2021

unwantedfocus said:
The blades do open for a bit but there should not be a 2mm hole I think. I also attached a video hope that helps you somehow.

Yeah, totally makes sense. I've not re-opened this camera just yet (working on another), but this is what I'd expect too based on experience with others. Thanks for the photos!

westopher · Jun 3, 2021

shutterfinger said:
My Prontor S uncocked
Self timer not set, blade controller tab has about .010 inch overlap of the self timer set/lockout, a potential problem, should be .0001 to .001 inch clearance.

Thanks for this series of photos. As I said in another post, I've not re-opened this camera since there's another one on the bench; now I just want to put that one aside and revisit! Thanks again.

westopher · Aug 16, 2021

Mamiya_Repair said:
On the Prontor-S, when using the delayed action, the blade operating ring is released immediately but a tab on the ring contacts the delayed action first gear segment and prevents the blades from opening until the timer runs down. You should be able to see this tab sliding along the delayed action escapement segment until a slot appears and the blades can open. Also, there is a spring located under the speeds escapement putting light tension on the blade ring to keep the shutter blades closed until the main spring opens them.

I finally had a chance to open-up this camera again. And yes, as everyone suggested, it was indeed a bent tab, and once corrected, it's working perfectly. Thanks everyone who responded for the assist. Very helpful indeed.

Prontor-S Delayed Action Weirdness

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