I have a very nice example of a Prismat PCA V-90 (1961-63), basically a Mamiya PH model with behind the lens leaf shutter. Unfortunately it has a shutter problem. Does anyone have experience with this model and its Seikosha SLV shutter? Symptoms include: When shutter is cocked the slow speeds run off before the shutter is even released. The shutter does cock and fire but the aperture blades remain stationary. I believe the mirror is droppng down normally as the shutter is cocked but I cannot physically see the mirror movement due to the rear capping curtain and the stationary aperture blades. Mirror frame will drop down in place if I pull it down manually via open camera back. Access to the entire Seikosha shutter is not easy; it's mounted behind a stout aluminum support frame. I was hoping not to remove leatherette to access the frame & shutter mechanism but maybe there is no alternative. I have thoroughly flood cleaned & recleaned the aperture blades and the shutter mechanism several times 1st using brake cleaner & then naphtha. Each blade is squeaky clean and shines. I would guess the problem is not gummed up parts or oily blades. Various shutter pivot pins look fine, line up, and move properly. Second problem: The reassembly steps for mounting the breech/bayonet lens holder back on the camera body is also a bit of a mystery. When I tighten the 3 mounting screws the aperture & shutter speed rings won't move freely back and forth within their maximum range despite care to align the various parts. Suggestions and guidance is appreciated.
I don't know this specific shutter but my best guess is that the shutter is not cocked completely by the cocking mechanism. On many shutters there is a spring-loaded crank arm from the cocking shaft which has a notch into which a tab of the blade actuating ring fits. If the shutter is not cocked far enough the notch will not 'seize' the tab on its return stroke, and the cocking shaft will not be latched by the release lever mechanism. So the cocking shaft will run freely - without actuating the blades. The cocking shaft also has an arm which hits the speed escapement, thus you will hear the buzzing sound when the shutter is set to slow speeds even if the blades do not open.
I think there is no other way than opening the shutter. On the Kowa SET (which probably is somewhat similar) you have to remove the front plate together with the lens mount and the speed/aperture ring.
