|
|
This topic comprises 2 pages: 1 2
|
|
Author
|
Topic: Help needed determining a scratch origination
|
|
|
|
|
Cory Johnson
Film Handler
Posts: 46
From: La Crosse, WI USA
Registered: Aug 1999
|
posted 05-08-2001 12:03 AM
I will try and answer as best I can. here goes:
Definitely not caused by a loop too big. I threaded it myself for the first 4 showings on a feature and the marking showed up.
Joe is right in that the "Middle" I mean the very right of the screen, but the markings tend to migrate towards the middle, and they always seem to happen the worse at the same spot: towards the middle on the very right side.
As far as the pad roller goes between the intermittent sprocket and lower feed sprocket, yes there is one there. Should I just remove it entirely? The sound flutter issue doesn't really apply(?) as the theatre has DTS.
I know it is not the DTS reader - it is less than a year old and the markings were there when the old one was in use. There were also times when we skipped the reader (non-DTS film) and the markings still appeared.
I believe it isn't the platters (Strong Auto programming platter), I am also on the same lines as Joe. If the markings are in a pattern, always at the same spot, it can't be a circular motion roller. I has to be something else.
I will check on the emusion side. I actually put a different film gate and shoe in the projector, but the markings still showed up.
Heres something else to consider: The projector actually froze up last Thurs (for no apparent reason) and we ended up having to have the intermittent replaced with a rebuilt, along with the usual coupler replacement to go along with it. Now, the marking appear further in on the film and are more noticeable. What could they have altered to cause this? Something in the alignment of the intermittent sprocket and shoe on the film gate?
We have been going around on this issue for years and we get no where because our techs don't know what to say because everything checks out perfectly on inspections. Yes, we have turned the blind eye for a while, but you are right that it is noticeable when moving the print to a different theatre. We are just hoping to throw the 35's out the window anyways and go with simplexes. The 35's are a large pain the ass along with our 1 remaining Xetron lamp house.
I will remove the roller as suggested, unless someone has a specific reasoning why not to. I will check the guide rollers, but am 99% that they are also correct. Keep the suggestions coming - hopefully we can nail it down to something... Thanks for all the input.
| IP: Logged
|
|
|
|
Paul G. Thompson
The Weenie Man
Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000
|
posted 05-08-2001 01:04 AM
Gordon, Those rollers on the Ballentyne have caused more scratches than you can shake a stick at, even when they were new. Strong international FINALLY modified those rollers so that on pulldown, the film "cupping" will not come in contact with the center of the roller, which caused nasty horizontal scratches as the film slams against the center of the roller. Even the new ones raised cain with film scratching, but not nearly as bad as the older style. The newer rollers were cut out deeper in the center than it was on the edges. (It was not straight across).I was told by Strong International people that the only reason for that roller is to reduce loop noise, but that machine is still very quiet without it. I have not noticed any change in sound flutter during tune-ups without that roller. If the projectionist threads up his machine and the loop passes equally above and below the shaft hole by observation when the machine is inched forward, the lower loop will be the correct size. It isn't any bigger than a Brenkert or a Century. The model VII Ballentyne soundhead is not the greatest soundhead in the world. Most of the flutter I have seen is caused by the scanner bearings being rough, the damper assy is shot, or there are major build-ups of crud and corruption on the timing belt pulleys or the belt tensioner, improper belt tension, a faulty timing belt, not to mention the friction "O" ring deterioration on the sound head stabilizer flywheel. Other flutter problems were caused by the projector not running at a constant speed for one reason or another.
| IP: Logged
|
|
Brad Miller
Administrator
Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99
|
posted 05-08-2001 04:32 AM
Cory,Three things to test. First, take a brand new trailer and run it yourself without the aperture plate in the machine 8 times in a row (double what it took for the scratch to show up on a brand new print). If the scratch is not there, you have just found your problem. Next, if the scratch is still there it sounds like either a loop scratch (from making the loop too big or too small). Try performing the same test with larger or smaller loops. Finally, if that still isn't it, then I would look for a misalignment on the shoe or a rough spot. I can't think of anything else that it could be since you clarified that the scratches do not run continuously from top to bottom of the picture.
| IP: Logged
|
|
|
|
|
|
|
|
Paul G. Thompson
The Weenie Man
Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000
|
posted 05-08-2001 01:38 PM
Gordon is correct about the lateral curve in the gate. There are two gate gauges - a "77" and a "75". Using the wrong gauge in the wrong film trap will present problems. It is not a good idea to change the intermittent sprocket without the correct gauge. Unstable picture with or without the "lay-on" roller is common in the older machines because of a poor trap design, and the coupler bobbins are all hammered to shit because the outboard bearing was grossly mis-adjusted and made too tight, or the outboard bearing is shot. The new trap Ballentyne designed is much more superior to anything they had. Place your fingers on the outboard bearing assembly and start the machine. If you can feel it throbbing, the bearing and/or coupler is shot. Then, walk up to the screen, eyeball the picture, and you will probably see a slightly unstable image.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 2 pages: 1 2
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Printer-friendly view of this topic