Film-Tech Forum ARCHIVE: intermittent platter problem

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Posted by Lee Akin (Member # 2178) on 01-30-2004, 11:45 AM:

I have an intermittent problem with my platter. about 4 times now in the last week the take-up has failed to start up. The voltage regulator arm continues to drop down until it bottoms out and shuts down, then the film spills out on the floor. Usually I catch it while it's still leader on the floor. Also the pay-out by this time has wrapped around the brain several times. Here is how I've been coping. First I spin the take-up platter by hand until I wind up the slack. Then I crank the projector by hand until the brain wrap frees up. Usually by this time the first trailer has started so I go turn down the theater volume. then I roll it by hand a little while more and I can tell the take-up is responding. Then I turn it all back on and it works!

First of all, what is causing this?

Secondly, is there a better method if it does happen again?

I don't know too much about the platter. It is a used ballantyne platter with 48" tables.

Thanks for any help you can provide.

Posted by Gordon McLeod (Member # 33) on 01-30-2004, 12:30 PM:

First rule one post the make and model of all the involved equipment as you post tells nothing about what are the inter-relating issues that may be involved
It is like going to the doctor and say cure me I am sick over the phone and no other details

Posted by Paul G. Thompson (Member # 655) on 01-30-2004, 01:37 PM:

Just from the sound of it, you have a variac-based platter - probably a Strong International, Potts, CFS, or some other off-the-wall machine that uses a variac for the base operating platform.

My thoughts are your variac is shot and might need replacement. But it is hard to tell. As Gordon indicated, give us the info and we can probably nail it down a little closer.

By the way, you can still run your show. Most variac based platters can be operated in an emergency with the MUT, but it will require constant attention.

Posted by Brad Miller (Member # 2) on 01-30-2004, 02:05 PM:

Just an FYI

quote:
I don't know too much about the platter. It is a used ballantyne platter with 48" tables.

Posted by Chris Hipp (Member # 1788) on 01-30-2004, 02:15 PM:

Rule out the simple explanations first:

Is the film wrapping around the brain as you thread the platter? If so try using a different brain, that one might need calibration.
Or your motor may be slow.

From what you are describing it sound to me that the platter isnt keeping up with the speed in which you are threading and it is engaging your tension sensing failsafe. I come to this assumption because you arent actually doing anything to fix the problem other than "cranking by hand" ( I dont understand what you mean exactly by that).

If you do have a tension sensing fail safe or "wrap detector" installed you can tighten it up so it wont engage and you will be able to run that first trailer through just fine.

This happens a lot with my new trainees, they call me over and I find nothing wrong so this could be the only explanation.

Posted by Dominic Espinosa (Member # 2122) on 01-30-2004, 02:31 PM:

From what you said it sounds like the problem is every deck on this specific platter tree? If so, then something is seriously off kilter. As was mentioned above you may need a new variac.
I'm not sure about your platters, but if you have one platter that's just not keeping up it could be out of calibration (if your platter even allows you to adjust the speed of the individual decks, which it should). Otherwise if it's all of them you'll have to look into it more specifically.

Also, I've had a problem with the Potts platters having worm "tires" on the drive rollers. This of course causes the platter to move slower. The system would counter this by speeding it up, which you'd definitely notice and it would be a gradual problem.
Post up your model numbers and some more details. We're all quite eager [Smile]

Posted by Lee Akin (Member # 2178) on 01-30-2004, 03:04 PM:

well, first of all, I'm a newbie, so please excuse my ignorance. I've had my theater up and running for about ten weeks now.

Where might I find model numbers and such on a platter. All I can refer to is the invoice of what I paid for and it says "used ballantyne platter system" It has a variac, or what I think is a variac at the bottom with an arm that goes up to a "W" to control the speed of the take-up platter. I tried calibrating timing but it is pretty difficult with this model, I think. when it stops working, though, it isn't a matter of it running too slowly. it just doesn't run at all, which leads me to believe it isn't a timing issue or tires or such. And, again, the problem is intermittent. I have been too frazzled at the time that it happens to remember if all occurences happen on the same take-up platter or not. my "shoot from the hip" guess is that it is the variac giving out on me. would that happen intermittently, though?

Thanks again

Posted by Dennis M Dow Jr (Member # 1970) on 01-30-2004, 04:24 PM:

lee
Might want to check the brushes in the variac as they tend to go bad.

Posted by Marc Jones (Member # 29) on 01-30-2004, 11:44 PM:

Lee
there are 2 potential compents that can fail with in the variac, 1 the brush or or the contact to the disk either will cause intermitant contact, you should see this problem iregardless of which platter your rewinding back onto. Note if you get into a bind and if you have a spare makeup table you could possibly steal the brush out of it.

Posted by Paul G. Thompson (Member # 655) on 01-30-2004, 11:51 PM:

Be careful, though. The variac on the platter could have the winding damaged. If that be the case, the brush may not fix it. Then you will be facing a situation where both the MUT and the platter are down.

Posted by Rick Long (Member # 213) on 01-31-2004, 12:33 AM:

I have encountered this problem with this platter several times in the last few years. The reason for film on the floor is, as you describe, the fact that the take-up motor is not taking up fast enough. The reason for this, MAY be that the elevator is not able to drop due to force of gravity, but instead, is stalling at some point on its way down.

Quick check to see if this is the case - prior to starting the show, but with the platter threaded, release the motor from the deck selected for take-up and slowly back it up until the elevator reaches the bottom. Remember though, as you said the problem is intermittent - it may take several trials to see if this is the case.
If you notice a "stalling or sticking" of the elevator the following may help:

(1) De-power platter.

It will be necessary to disconnect the elevator arm from the variac. On the newer Ballantine platters, this is simply done with a 1/8" allen key. Remember to mark the sections before removing so that they may be replaced in approximately the same position.

Now it will be necessary to withdraw the rotor shaft. This is done by rotating the shaft or the brush head on the variac until two screws (about 90 degrees apart) become visible between the metal variac brush head and the variac itself. Using a long 1/16" allen key loosen these screws about two turns. The shaft may now be withdrawn through the other end.

Where the shaft went through the hole into the variac may be found a small black grommet. It has been my experience that these grommets are responsible for this elevator sticking. Simply remove it and re-install.