Film-Tech Forum ARCHIVE: Kinoton FP-75E

This is topic Kinoton FP-75E - Stutters in forum Large Format Forum at Film-Tech Forum ARCHIVE.

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Posted by Randy Stankey (Member # 64) on 06-10-2012, 01:28 PM:

Just a strange behavior I noticed and wondered if it was a problem brewing, if it is a leftover from the last problem we had or if this is a "mostly normal" behavior.

When the projector (Kinoton FP-75E) starts up, the film begins in continuous motion. Then, after a few seconds it starts running with the usual intermittent motion. When it does, this, it takes about five seconds to stabilize. During this time the projector makes a stuttering sound and the upper/lower loops change size until the system settles and runs normally.

After this, everything runs fairly steadily. If you look carefully, you can see the loops oscillating but the system stays in stasis through the whole show.

Now... Here is where things get funky.
On my last show, which started only 20 minutes ago, the projector started up normally and ran for about half a minute then suddenly started stuttering again. The loops oscillated and chattered. Then, as suddenly as it started, it settled and ran normally.

As of my last check, a few minutes ago, everything is running all right but, now, I've got this question.

Is this within range of normal behavior or do I have a problem brewing?

P.S. -- Just went to check the projector a minute ago. The sound is out of sync. The Aquilla T/C generator is running about 10 or 15 seconds ahead of the Fostex digital playback unit.

No, this ain't normal... [Frown]

Posted by Steve Guttag (Member # 268) on 06-10-2012, 02:00 PM:

First off...if this is an FP75E, then this is the wrong forum since it tops out at 5/70. If it is an MP75E then this may be the right forum since it tops out at 8/70

What you describe is mostly normal but it might also be a clue as to the other problem. The shutters in an "E" projector have an idle speed and then one dictated by the pulse/tach that lets the shutter know how fast the sprockets are running. The intermittent movement also is using the pulse/tach to know when to pull down. The intermitttent also knows when the shutter is blocking the aperture or isn't. The intermittent will not pull down if the shutter is not blocking the aperture.

Since the shutter has a bit of mass (and in an 75 series it is also driven by separate inverter, belt and motor...one has to deal with the physics of the shutter changing speed. That is, it will take time for it to react to the sprocket speed change...which it is fluctuating in speed, one is bound to see the loops stutter until the new stable speed is settled upon. Again, due to the masses involved, for some speeds, it may never completely stabilize but normally for regular 24fps type stuff...one is in the sweet spot of the system, by design so it should stabilize.

If your sound syncs to the projector...then again, the pulse/tach is what is driving that with a quadrature output.

It seems to me that from the symptoms you describe, I would start my investigation with the tach, and its wiring...make sure it is being driven properly and is putting out clean pulses.

Also, check your belts since if they have too much slop...it will cause the whole system to have an imprecision that you describe.

Posted by Randy Stankey (Member # 64) on 06-10-2012, 02:23 PM:

Yes, it's 8/70.

The stutter at startup, I thought was normal within limits. I wasn't too worried about that.

The stutter AFTER startup had me worried but worn belts sounds like a likely cause. So long as I have some idea of what's going on, I'm not too worried. I can check the belts at the end of the day, today. If they are going slack, I can tighten and/or replace them at the next opportunity.

The time code doesn't always run PERFECTLY in synch, to the frame but it's usually close enough that you have to look closely in order to tell. 15 seconds is way more than there should have been. Again, a slipped belt might explain that, too.

Thanks! [Smile]

Posted by Randy Stankey (Member # 64) on 06-10-2012, 07:48 PM:

BTW: Figured out the sync issue...

Some dummy accidentally hit the 25 F.P.S. button. [Embarrassed]