Kinoton electric douser issue

[Casey Sanders]

Running into an issue with a pair of Kinoton FP38 E projectors: when we change over from left to right, the electric douser on the lefthand side does not fully close.

I’ve opened the shutter housing (while powered down) and can see several adjustable mechanical components related to the electric douser (which I've color-coded in the photo attached):

- a spring (yellow)
- a small piece of metal which the spring hooks onto (red)
- a stopper/counterweight? (green)
- a damper (blue)

(The manual does not name the above pieces or illustrate how they interact, so I am making some assumptions!)

In the "closed" position, the spring in the left projector (the problem projector) is slack compared to the spring in the right projector. I assume that that's our issue: that the tension of the spring is what pulls the douser into the "closed" position, and that the spring in the left projector is not taut enough to achieve that.

My thought is that the angle of the (red) piece of metal could be adjusted to increase the tension of the spring, and that the (blue) damper could be repositioned closer or farther from the (green) stopper to account for any "bounce" that the change in the spring tension might create.

Could anyone with Kinoton experience weigh in on this? Do I understand this mechanism correctly, or somewhat? Is this sound reasoning? Could something else be the culprit? Could adjusting these components produce any undesired results?

[Steve Guttag]

The spring is what applies the closing force. It gets its tension not just from the red tab (it is an electronic male push connector that Kinoton repurposed into a spring connection point) but also from the green block. There is a set screw that secures the green block to the dowser pivot shaft. If that block has slipped on the shaft, you could get into the condition you are in.

Compare your "good" machine with respect to how far the block closes (push it with your finger) to see if they are at the approximately the same position, when fully closed (and fully open...move the dowser blade manually on each).

Ideally, when the dowser closes and is fully closed, the block is square with the damper piston. The damper is adjusted to prevent dowser bounce when it closes. If it is too strong (engages too soon) the dowser won't close all of the way because it prevents it. If it is too weak (engages too late), the dowser will bounce and remain partly open. Ideally, the dowser blade closes without bounce.

In a changeover system, you can also work with the spring and block (and, to a degree, the damper) to get the speed of the two dowsers better matched so that the changeovers are more seamless. Remember too, too much spring tension adds to the bounce and slows down the opening speed. So, it is a delicate balance.

[Casey Sanders]

Steve: Thank you so much for this info. I made a few slight adjustments to these components with your comment in mind.

I adjusted the angle of the tab in order to tighten the spring. Still, it was visibly more slack than the “good” spring in the other projector.

To tighten the “bad” spring further, I adjusted the angle of the block which sits on the pivot shaft. Now the spring is tense enough to pull the douser into the “closed” position much more efficiently — it’s closing every time! Big win. However the douser seems to be closing slowly (enough that there’s a frame or two of overlapping image from both projectors), and it does bounce slightly, as the block (at this new angle) is no longer engaging with the piston of the damper.

I wonder if I need to tighten the spring itself by a coil or two (or replace it entirely with a tighter spring) in order to create more tension WITHOUT changing the angle of the block on the pivot shaft relative to the damper, so that the spring will pull the douser into the “closed” position more quickly, and so that the block will meet the damper squarely (like it did before) and mitigate the bounce. Might that be a fair assessment?

[Steve Guttag]

Sure, anything is possible.