Film-Tech Forum ARCHIVE: Sound tension issue on start up

This is topic Sound tension issue on start up in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Chris Simpson (Member # 5953) on 04-04-2011, 04:18 PM:

Hey all! this is my first post so I will introduce myself first.

I am Chris, I work at the Denver FilmCenter on Colfax (old neighborhood flix) I've been a lurker here for awhile and know some of ya, so hello!

my problem,
we run with Century projectors and I can't figure out why the tension of the film around the sound drum changes sometimes upon start up, and rarely it tightens up so bad the film breaks.

here is a link to the picture I took of the sound reader area.
http://i24.photobucket.com/albums/c27/Tsaier/bb5abbf5.jpg
this has a normal non tight tension.

Could it be the belt from the motor slipping? I am almost positive it's not film jumping the sprocket. any ideas?

Thanks! glad to finally have posted!

Posted by Randy Stankey (Member # 64) on 04-04-2011, 05:22 PM:

The sound head drives the projector head. If the linkage between the two fails, the projector can fall behind the sound head, causing the film tension between them to change.

If the linkage is slipping it could be the belt or the gear drive but don't forget to check the main gear at the bottom of the vertical shaft which is inside the back side cover, all the way down at the bottom.

Posted by Kurt Zupin (Member # 2751) on 04-04-2011, 05:57 PM:

Welcome to the boards, but a headsup before a mod shows up and deletes your link, if your going to post a picture you need to upload it to the site. That way it won't vanish one day, it will be on the site for future thread readers.

Posted by Brad Miller (Member # 2) on 04-04-2011, 06:13 PM:

Is this reel to reel?

Posted by Joe Redifer (Member # 3) on 04-04-2011, 06:16 PM:

No, they have platters. But for whatever reason I thought they used Simplexes, not Centurys. Maybe someone recently did a swap.

Posted by John Wilson (Member # 269) on 04-04-2011, 06:21 PM:

Here's the linked picture for the archives.

It could be the lay-on rollers not being set to 2 thicknesses of film. If it's more, when the platter pulls it may be yanking the print over the sprockets on the soundhead sprocket.

What sort of platter are you using. Have you been there to witness this happening or have you just seen the result?

Posted by Joe Redifer (Member # 3) on 04-04-2011, 10:54 PM:

I think they have Neumade platters (they may be labeled as Xetron, not sure). I talked to somene who used to work at this place long, long ago and he said this was an issue even back then. Some machines have too much tension and others not enough. Platters had dents in them that he hammered out and overall it really is a lovely place. I've never been there, maybe I should go over and fix the place up.

Posted by Monte L Fullmer (Member # 2797) on 04-05-2011, 12:56 AM:

..or, the rear door that covers the flywheel is dragging a bit on the flywheel causing back tension, or the scanner drum bearings are dragging themselves...

...we need the ol' fluid filled, dampner flywheels to reduce these dragging startups..

p.s. - back in the booth now.... - Monte

Posted by Vern Dias (Member # 5241) on 04-05-2011, 08:20 AM:

Way back when I worked at the Village theater in Boulder CO. we had some crap Westrex Century knockoffs for projectors in houses 2, 3, and 4, and we had this kind of issues as well.

After a lot of frustration and troubleshooting, the problem turned out to be a combination of unhardened set screws in the soundhead drive pullays and the lack of flat areas on the shafts allowing the pulleys to slip on the shafts. This will cause the symptoms you are seeing and is very hard to find.

Vern

Posted by Eric Robinson (Member # 2966) on 04-05-2011, 10:18 AM:

Although the platter could pull the film tight, it seems unlikely.

I think the scenario that Vern describes (above) could be a possibility amongst others. If the Century is standard drive, then the diagram below shows one possible culprit whereby the pulley which drives the projector head is slipping, thus causing the sound head sprocket to turn more than the projector head sprocket over a given period of time.

Posted by Robert Throop (Member # 61) on 04-05-2011, 11:32 AM:

The tension idler could be slightly loose causing BE 529 to jump teeth.

Posted by Louis Bornwasser (Member # 3063) on 04-05-2011, 07:11 PM:

I'm with Eric on this one. louis

Posted by David Zylstra (Member # 4230) on 04-05-2011, 07:47 PM:

I have had this problem many times before on gear belt driven Century projectors with varying causes:

As Eric shows - the pulley might be slipping

As Robert says the idler roller might not be set properly and might be allowing the belt to to jump teeth on startup

The bracket (AR-0178) holding the pulley side of the sprocket shaft might be loose allowing the pulley/shaft to pull up on startup which lets the belt jump teeth

The bearing on the pulley side has worn out and has enough play to let the belt jump teeth on startup tension (if this is the case the shaft is probably also worn where the bearing holds it)

There may also be motor issues depending on which motor you have - some from the late '80s had slow start kits (usually a grey box under the motor mount housing a bank of resistors and a relay) that sometimes had issues aloowing the motor to jerk at startup.

Posted by John Wilson (Member # 269) on 04-19-2011, 03:42 PM:

So...what was it?

Posted by Mark Gulbrandsen (Member # 72) on 04-20-2011, 02:08 PM:

Man, that is one crusty old Century! Send it to Louis for a rebuild and repaint! You WILL feel better about it then.

Posted by David Deserranno (Member # 6227) on 05-01-2011, 01:22 PM:

Hi im new to this forum also , we are having the same type of of problem except it is occuring at the film splice it seems to be dropping tention in the intermitent any ideas on what could be going on

Posted by Phil Ranucci (Member # 3820) on 05-01-2011, 02:11 PM:

The pad rollers on your machine could be set too loose allowing the splice to jump a tooth. What kind of projector?

Posted by David Deserranno (Member # 6227) on 05-06-2011, 07:42 PM:

it is a century projector

Posted by Tony Bandiera Jr (Member # 2365) on 05-09-2011, 12:00 AM:

David, check your film trap alignment. If the rails are too close together you will have issues at the splices.

Also make sure the shoe assembly on the intermittent is not loose and is closing properly. You can get instructions to adjusting it and the trap rails in the manuals available on this site. But I strongly urge you to have a tech in to look at it if you are not 110% confident you know how to make those adjustments.