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     Steve_s Tinkerer Username: Steve_s Post Number: 56 Registered: 07-2006 Rating: N/A |
Since my last posting I decided it was time I tried to work out for myself just how these Prakticas work. They seem to have far more levers and interlocks than can be good for them! I took the delay mech. off my "scrap" PLC3 which had already had the front panel removed. I have not considered the mechanism of the shutter itself, only the cocking mechanism on the top-plate, and the release/mirror mechanism on the front-plate. SHUTTER COCKING MECHANISM: - The pawl at 2 0'clock under the wind lever engages with one of 3 slots and turns the sleeve on the wind spindle anti-clockwise (all the gears are part of the film transport, nothing to do with the shutter). The large complicated lever at 6 o'clock relative to the wind lever (I'll call it "A") is pulled to the right by one of 3 pins on the wind sleeve. Through a link, this turns clockwise a lever (I'll call it "B") which rotates round the speed control spindle. It is low down and not easy to see. It has a part at 8 o'clock bent down at 90º which I will mention later, and a vertical pin at 12 o'clock. The pin turns the big lever at the top under the speed control (I'll call it "C") which releases the wind-lock ready for it to fall into the next of 3 slots in the wind sleeve. Lever C continues to turn until it is caught by a latch, part of which sticks out horizontally below it at the top left. At the same time, lever A cocks the shutter by pulling a long flat strip at the back to the right, and levers A and B and the strip all then fall back to their start positions. When the shutter is fired, lever C's latch is released (see below), lever C turns anti-clockwise and the pin sticking up on it pushes the curved lever at the left, which moves the longer of 2 vertical levers right at the back, which releases the first (lower) shutter blind. The upward tab on lever C then meets a lever on the delay mechanism which slows it down by an amount dependant on the speed setting. After the delay, part of lever C meets the shorter of the 2 vertical levers, which releases the second (upper) blind. Finally lever C lifts the wind-lock out of its notch ready to start the process again. SHUTTER RELEASE: - As the shutter is cocked, the part of lever B with the downward bend (right at the left of the cocking mechanism), moves forward pushing a vertical lever on the mechanism which is attached to the front plate until it latches in its forward position. This lever (I'll call it "D") is attached to 3 springs which are tensioned as it moves forward (It also has a slot in it in which the "tail" of the viewfinder cocked/uncocked indicator fits). When the shutter release button is pressed, the centre of the 3 springs lifts the mirror, and at the same time the left-most of the springs pulls a lever rapidly forward, which releases the latch for lever C and starts the shutter firing operation. Finally, when the second blind releases, a pin on the shutter moves to the left, which operates a lever (pointing to the right, level with the back of the prism), which releases the latch on lever D, and the 3rd spring returns lever D to its start position and the mirror to its normal position. This sequence is correct as far as I can see, but I'm open to correction. Your lever C was obviously in the cocked position, and you have already found its release latch. The screw you mention in the slot at the top provides adjustment of the tension of the spring which returns lever C (there are also 2 options for the position of the tail of the spring) and this will alter the overall timing of the shutter speeds. If you have to dismantle anything here, make sure you mark this so you can put it back where you found it. The reason you can't see the centre spindle in the speed control (well spotted!) is that the photo is of an LB2, which doesn't have through-the-lens metering. It seems as though you have now got everything on the top-plate into the uncocked position, and since you can see the tell-tale in the viewfinder, presumably your lever D is in the uncocked position. You can check this if you look down to the right of the prism. Just to the right of the prism mounting screw you will see a dog-leg lever which is the tail of the tell-tale. You will see that this fits in a slot in a lever, which is lever D. Uncocked, the top of this lever should be about mid-way betweem front and back of the camera. In its cocked position it will be right at the front, and hard to see. Its release latch is the lever you can see in the photo at the bottom left, just top left of the screw head (push it to the left). All I can suggest is that you try to work through the system pushing and pulling things manually to see if you can find what is jammed. Check first that there isn't anything jamming the film transport gears, and that the pawl that engages with the wind-sleeve is correctly positioned (it can escape from its return spring when you are poking around down there). If you try to push lever D forward be VERY careful. Its springs are strong and when I tried it I broke off the rear corner at the top of the lever! It is quite easy to take the front plate off, by the way, but you do have to remove the covering. I'm afraid it's all a lot of work for a camera that isn't worth much, but at least if you succeed you will get much more pleasure from using it in future than if it had never failed! |