Mir problem

[fanshaw]

I have a Mir (Zorki-4 w/o slow speeds) that has suddenly seized up. The shutter doesn't fire and the wind on knob won't move unless the rewind disengagement collar is depressed. When the collar is depressed the wind on knob can be rotated, but the shutter isn't cocked.
I would be grateful for any suggestions about the likely cause.

Fanshaw

 

[wolves3012]

I can think of several reasons. Firstly, is the shutter cocked but refusing to fire? Or, is the wind-on jammed so that you can't cock it? If it's cocked, can the release be pressed or not? Is the wind-on absolutely jammed solid or is there a little "give" in it?

Film chippings in the restrictor gears, failure of the two pins below the sprocket to disengage when the shutter release is pressed. Ratchet failed or gummed up could stop you winding on. These are some of the things that spring to mind.

Sounds like you will probably have to do some dismantling. If you study the "HOW TO - ZORKI 4K" sticky it'll give you an idea. I don't have a Mir to refer to but my understanding is that it is a 4 with the slow-speed escapement missing and fewer selector settings. The 4K is so similar that you should be able to use my "HOW TO" and skip the obvious sections. Removing the winder is simply a case of slackening the small grub-screw and unscrewing the knob, you can ignore the bits about the wind-lever.

Try and give us a little more information about the exact nature and it may help find the areas that need checking.

 

[fanshaw]

Mir problem

Thanks very much for your comments.
The shutter button can be depressed easily. The wind-on knob is locked solid, so I would think that it is not just dirt in the mechanism. It feels like the shutter is cocked but will not fire, but I don't know for certain that this is the case.With the rewind release depressed the film transport shaft with the sprockets rotates easily in both directions. The two pins below the shaft move up and down when the shutter release is operated.
I am sure the 4K dismantling info will be a great help, although I am not experienced in repairing cameras I will have a go!

 

[wolves3012]

Try and establish if the shutter is cocked or not - check the curtain positions if you can get to figure which way they travel. If the shutter is cocked and failing to fire, then the locked winder is to be expected. Once you press the release button, the two pins below the film sprocket should be disengaged enough to clear each other.

At that point, only a couple of things can hold the shutter blinds from releasing and that's the restrictor gears or something fouled in the speed selector. A broken or untensed spring in the tension roller(s) would also cause a problem, but the slack shutter curtain would be easy to spot.

You need to apply some logic to this and try and trace the area at fault, otherwise you can end up stripping half the camera when undoing a couple of screws might give access. Alternatively you could strip the whole camera and give it a good CLA while you're solving the problem!

If you're not experienced in repairs then make sure you follow the introduction part on my HOW-TO, containers for parts, work area, tools needed and so on. Ideally, use a digi to record steps and take "before" shots. The Mir should be an easy camera to work on, based on my experience of the 4K, so at least you won't have a baptism of fire!

Let us know how you get on - if you're stuck on something just stop at that point and see if we can help.

Good luck!

 

[fanshaw]

Mir problem

Thanks again. I think that the shutter will not fire for some reason. The two pins that you mention are disengaged. There isn't anything odd about the appearance of the shutter blinds, they appear taut. Thanks for your encouragement. I will take the top off if I can, with the help of the Zorki-4K notes and see what I find. I'll let you know how it goes.

 

[fanshaw]

Mir problem

Well, I have taken the top off, but there is nothing obviously broken, so I am not any wiser. If I depress the shutter and release it, I can turn the wind-on knob but the curtains don't move.Any suggesstons as to what what to look at ?

Try and establish if the shutter is cocked or not - check the curtain positions if you can get to figure which way they travel. If the shutter is cocked and failing to fire, then the locked winder is to be expected. Once you press the release button, the two pins below the film sprocket should be disengaged enough to clear each other.

At that point, only a couple of things can hold the shutter blinds from releasing and that's the restrictor gears or something fouled in the speed selector. A broken or untensed spring in the tension roller(s) would also cause a problem, but the slack shutter curtain would be easy to spot.

You need to apply some logic to this and try and trace the area at fault, otherwise you can end up stripping half the camera when undoing a couple of screws might give access. Alternatively you could strip the whole camera and give it a good CLA while you're solving the problem!

If you're not experienced in repairs then make sure you follow the introduction part on my HOW-TO, containers for parts, work area, tools needed and so on. Ideally, use a digi to record steps and take "before" shots. The Mir should be an easy camera to work on, based on my experience of the 4K, so at least you won't have a baptism of fire!

Let us know how you get on - if you're stuck on something just stop at that point and see if we can help.

Good luck!

 

[wolves3012]

OK, next questions then: If you can turn the wind-on without having it in "rewind" - does the wind knob turn freely or does it move the sprocket shaft too (such that the sprocket isn't free)? This is beginning to sound as if the rewind-release is stuck on rewind...Is the sprocket shaft free to turn in both directions or is it latched in the "drive" position?

 

[fanshaw]

Mir problem

It is latched in the 'drive' position. When I depress the shutter release and release it I can turn the wind on knob for a limited amount just as it would if the camera was behaving normally. The sprocket shaft turns and is locked in the drive direction. It is just the shutter blinds that do not move.

 

[wolves3012]

I'll think that over then - I can't think how the curtains can fail to wind if the knob turns the usual amount (as if it were winding normally)...That one has me puzzled!

 

[ChrisN]

There might be something in this thread http://www.rangefinderforum.com/forums/showthread.php?t=5442&highlight=mir that may help.

 

[fanshaw]

Thanks Chris, it seems that your experience was very similar to mine. I shall see if I can locate the cam that may be out of place.

 

[fanshaw]

I'll think that over then - I can't think how the curtains can fail to wind if the knob turns the usual amount (as if it were winding normally)...That one has me puzzled!

Now I find that pressing the release doesn't always allow wind on!

 

[wolves3012]

Ok, I've had a dig into my "parts" 4K to confirm how I thought it worked. There's a winding system, which is a gear train that transfers motion of the winder to the sprocket. There are clutches and ratchets in that train but they aren't important for the purposes of understanding this problem. The point is, winding the knob/lever causes the film sprocket to rotate.

On the bottom of the sprocket there is an offset pin, which engages with a pin on a disc below it - the disc is on a shaft and on the very bottom of that is a gear, so the gear turns when the sprocket turns during winding. That gear drives another, which in turn drives a gear which is attached to the shutter curtain drum shaft. That gear has a circular slot cut for most but not all of it's circumference. The gear sits over a pin in the bottom of the crate. The pin means the gear can only turn for most of one revolution, but it's limited in either direction to less than one turn.

Now, from the above you may see why I can't envisage the problem! The limiting mechanism in winding is attached *directly* to the curtain drum - that means that if the winder moves only a limited amount then that *has* to be caused by the curtain drum turning, which means the curtains *must* be moving (if they are attached, which I'm sure you would notice if they were not!). I'll post some pictures of these parts later, hopefully it'll help you see how the mechanism works.

Incidentally - where are you? I'd be willing to take a look at it for you if you wanted...

 

[fanshaw]

Mir problem

Ok, I've had a dig into my "parts" 4K to confirm how I thought it worked. There's a winding system, which is a gear train that transfers motion of the winder to the sprocket. There are clutches and ratchets in that train but they aren't important for the purposes of understanding this problem. The point is, winding the knob/lever causes the film sprocket to rotate.

On the bottom of the sprocket there is an offset pin, which engages with a pin on a disc below it - the disc is on a shaft and on the very bottom of that is a gear, so the gear turns when the sprocket turns during winding. That gear drives another, which in turn drives a gear which is attached to the shutter curtain drum shaft. That gear has a circular slot cut for most but not all of it's circumference. The gear sits over a pin in the bottom of the crate. The pin means the gear can only turn for most of one revolution, but it's limited in either direction to less than one turn.

Now, from the above you may see why I can't envisage the problem! The limiting mechanism in winding is attached *directly* to the curtain drum - that means that if the winder moves only a limited amount then that *has* to be caused by the curtain drum turning, which means the curtains *must* be moving (if they are attached, which I'm sure you would notice if they were not!). I'll post some pictures of these parts later, hopefully it'll help you see how the mechanism works.

Incidentally - where are you? I'd be willing to take a look at it for you if you wanted...

Thanks for all your advice. It is particularly kind of you to offer to look at it. I am in NE England so i would have to post it to you.

 

[wolves3012]

Right, here's some pics of the pertinent parts in a 4K (I'm assuming the Mir would be the same). First pic shows the curtain drum gear in mesh with the intermediate gear (driven off the sprocket gear and pin). Second shows the underside of the drum gear - note the almost full-circle groove. Third pic shows the pin that limits the curtain drum gear. Now you can see that it's the drum gear that stops the wind action. If this final gear isn't engaged, for whatever reason, the winder will wind freely as far as you like BUT the curtains won't be wound.

What I really suspect your camera is doing is that the shutter is cocked but isn't actually firing (reason unknown). This being the case, when you press the shutter release it *might* be allowing just enough movement to let the sprocket pin past the other drive pin, allowing you another turn on the winder but doing nothing else bar turning the sprocket.

You could establish whether the shutter is cocked as follows: Remove the back & lens. Now, with nice clean fingers (!), pinch the curtain gently through the back & front of the camera. Try to pull it GENTLY towards the right (sprocket end). If it's not cocked you will be able to move the curtain against the rewind springs and you'll see the metal lath appear at the left of the frame. If this is so, let it back gently. If it's cocked there will be little or no movement of the curtain. Needless to say you should absolutely NOT use force or you could pull the curtains/tapes off their drums.

As regards posting the camera to me to look at, it depends if it's worth it to you in terms of postage costs and if you trust our dear old posties not to lose it. Special delivery or recorded first class are the only ones I trust. That would be in the region of £10 both ways. Up to you, I'm not promising I can fix it, especially if something is actually broken (though I do have the "parts" 4K to raid!). I wouldn't need the lens, of course.

 

[fanshaw]

Thanks for this info. I will study the pics and have another look at the works of my camera.
I have done your shutter curtain test and I was able to pull the curtain against the spring, so that proves that the shutter isn't wound!