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» Film-Tech Forum ARCHIVE   » Operations   » Film Handlers' Forum   » Potts Platter Takeup Problem

   
Author Topic: Potts Platter Takeup Problem
Mitchell Dvoskin
Phenomenal Film Handler

Posts: 1869
From: West Milford, NJ, USA
Registered: Jan 2001


 - posted 02-05-2009 11:35 AM      Profile for Mitchell Dvoskin   Email Mitchell Dvoskin   Send New Private Message       Edit/Delete Post 
An arts center that I run film for every now and again has a Potts Platter (or an early knock off) that has developed a problem. Occasionally the takeup platter stops, or does not start. It has happened 3 times, 2 of which were at startup, last night it happened about 15 minutes into the feature.

As their is no automation or safety interlocks on the projector, it merrily drops film on the floor, the "yo-yo" takeup rollers drop to the bottom cutting power to the entire platter, causing a brain wrap on the feed.

Fortunately, I was in the booth when this happened and by chance caught it in what appears to be under a minute (judging by the amount of film dumped on the floor). I shut down, fixed everything, and the remaining 2 hours ran fine.

I'm not a happy camper when film is damaged or dumped on the floor during my watch, and although I have been in the booth, I have not actually seen it happen. As a result, I haven't been able to determine exactly what the problem is.

These platters are not exactly high tech. It has to be one of:

1) The power rheostat has a dead spot. After the show I tried to find it moving the "yo-yo" manually, but no dead spots were found.

2) The takeup motor intermittently stops or loses speed, but motors tend to either work or not, and it ran fine for the next 2 hours.

3) The "yo-yo" is sticking, causing the takeup to run too slow, then "yo-yo" lets go and drops to the bottom cutting the platters power. Again, I can find no evidence of this happening.

I'm at a loss on how to proceed. Any help would be appreciated.

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John T. Hendrickson, Jr
Jedi Master Film Handler

Posts: 889
From: Freehold, NJ, USA
Registered: Apr 2001


 - posted 02-05-2009 01:38 PM      Profile for John T. Hendrickson, Jr   Email John T. Hendrickson, Jr   Send New Private Message       Edit/Delete Post 
Mitch-

You may have a bad microswitch in the variac assembly. Any idea how old it is? Try replacing it and see what happens.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004


 - posted 02-05-2009 02:15 PM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
It is more likely worn-out brush on the variac assembly. The problem will get worse fast if you don't fix it soon. As long as you replace it before the top of the windings where the brush slides gets burned, it is a simple and relatively inexpensive fix.

If you wait too long and fry the variac, don't waste money on the part from Potts or Strong. You can buy the same variac at a good electronics store and swap the shaft assembly (which is a unique piece but interchangeable with a stock variac.)

Contact Mark G at CLACO, I think he stocks the parts and can give instructions for the swap.

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99


 - posted 02-05-2009 04:03 PM      Profile for Randy Stankey   Email Randy Stankey   Send New Private Message       Edit/Delete Post 
I vote with Tony.

Check your variac.

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99


 - posted 02-05-2009 09:13 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
We do stock all the variac parts... Stator, Brush, Rotor, and center contact... usually the center contact comes off and what's left of it rubs on the rotor and the consequent arcing destroys the brass in a small area. The platter then becomes erratic.

801-355-1250

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004


 - posted 02-05-2009 09:20 PM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
Thanks Mark..now do I get a bonus check for the referral? [Big Grin]

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16657
From: Music City
Registered: Jun 99


 - posted 02-06-2009 01:34 AM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
The book keeper has to approve all sales comission checks [Eek!]

Mark

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Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 02-06-2009 02:44 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
Yea, had to replace a variac in one of our A-3 units. You oughta see that collector ring where the brass button makes contact at - all the chrome gone and horribly pitted.

I was experiencing the same, irratic rewind. the "W" roller assembly was having fits keeping steady.

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Mitchell Dvoskin
Phenomenal Film Handler

Posts: 1869
From: West Milford, NJ, USA
Registered: Jan 2001


 - posted 03-05-2009 10:31 AM      Profile for Mitchell Dvoskin   Email Mitchell Dvoskin   Send New Private Message       Edit/Delete Post 
This platter is becoming the bane of my existence. The above problems have been resolved, but I have now have a different issue. The theatre's tech director decided to take the variac apart to check the brushes and clean it one day when I was not there. He put it back together, and timed the platter according to the manuals instructions. However, now the takeup platter stops when the yo-yo is about an inch from the top, and comes up to full speed about 2 to 3 inches from the top. The problem is that when I start the show, the yo-yo drops almost to the bottom, causing the takeup to to spin very fast and not have time, due to momentum, to slow down before the yo-yo hits the top and snaps the film (acetate threading leader). We tried lowering the "off" spot on the yo-yo in relation to the variac, but that caused the yo-yo to hit bottom during startup killing the power to the platter.

What I have been doing is starting the projector and running over to the platter to manually slow the momentum of the takeup so the film does not snap. Once done, it runs fine for the rest of the show. Unfortunately, I'm not always there for film show, and I would like to get this fixed of other who may run shows.

To summarize this long winded post, the range of the variac, from stop to fast, seems to be taking place within 3 inches of each other, which does not allow for takeup momentum at the top of the yo-yo.

Any suggestions on how to proceed?

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Jim Cassedy
Phenomenal Film Handler

Posts: 1661
From: San Francisco, CA
Registered: Dec 2006


 - posted 03-05-2009 11:35 AM      Profile for Jim Cassedy   Email Jim Cassedy   Send New Private Message       Edit/Delete Post 
quote: Mitchell Dvoskin
Any suggestions on how to proceed?
Shoot the tech who screwed up the platter ! [Big Grin]

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Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 03-05-2009 12:53 PM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
What the reason why the tech had to fubar the thing in the first place?

Obviously, he didn't get the adjustments right to let the variac go back to mechanical zero.

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Adam Fraser
Master Film Handler

Posts: 499
From: Houghton Lake, MI, USA
Registered: Dec 2001


 - posted 03-06-2009 09:40 AM      Profile for Adam Fraser   Author's Homepage   Email Adam Fraser   Send New Private Message       Edit/Delete Post 
Mark, do you carry the Staco 291 variac for the early TECO platters? I have heard they are a Potts knockoff. The one I need is for the moving arm on the tree. The variac has an open frame, the only ones I can find have a dial on and are enclosed in a box for other uses.

Sorry to the OP for going off course.

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 03-06-2009 10:03 AM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Most of the TECCO's used a smaller variac than the potts

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Jarret Chessell
Master Film Handler

Posts: 288
From: London, Ontario, Canada
Registered: Jan 2009


 - posted 03-06-2009 08:38 PM      Profile for Jarret Chessell   Email Jarret Chessell   Send New Private Message       Edit/Delete Post 
Just one thought to put out... I've seen similar problems with platters that have become warped, the motor isn't making contact with the platter, so if the platter happens to be in the dead zone when it starts it just wont take up the film. (The motor usually spins wildly as the yo-yo drops before it hits the stop micro switch)

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Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004


 - posted 03-08-2009 03:03 AM      Profile for Monte L Fullmer   Email Monte L Fullmer   Send New Private Message       Edit/Delete Post 
quote: Jarret Chessell
I've seen similar problems with platters that have become warped, the motor isn't making contact with the platter, so if the platter happens to be in the dead zone when it starts it just wont take up the film
... and this is when you either crawl under the deck, or take it off the spindle, lay it face down on the smooth floor, get a pair of vise-grip pliers, pinch them on the deck support arms and pull sideways on them to straighten the arms out to square.

This usually gets the decks back to level since the aluminum isn't bent itself-just pulled down by the bent support arms.

But, if there is a crease in the aluminum, then good luck in getting things straighten out.

You just have to tell the people not to lean heavy on the decks, or splice on the decks themselve being so flimsy.

Christie decks - you can stand on them ....

-Monte

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