Film-Tech Forum ARCHIVE: Mysterious scratch

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Posted by Mike Blakesley (Member # 26) on 08-19-2006, 04:39 PM:

I was gone last week. The print we are running was in perfect shape when I left. Now, it's got this huge scratch running right down the middle of the print for about 25 minutes in the middle of the print.

- The scratch isn't stationary, like if there was a roller not spinning...it jumps back and forth over a small area and is a BIG yellow scratch (probably about 3/4" wide on the screen. It also comes and goes sometimes, but for the most part is steady.

- It starts in the middle of reel 3 and quits somewhere in the middle of reel 4, but from that point on is just an occasional black scratch, but in the same position.

- It's almost dead-center in the picture, but a bit closer to the soundtrack edge.

- We have a Simplex projector and an AW3 Christie platter, if that helps with any ideas.

We have no broken anything, the rollers all spin freely, the projector is clean.......I want to know how this happened so I can chew my substitute projectionist out appropriately, but I can't figure out how it could have happened right in the middle of the movie, and then sort of stopped, without warning. Any ideas??

Posted by Frank Dubrois (Member # 3042) on 08-19-2006, 06:47 PM:

Chew the projectionist out anyway. If it lasts 25 minutes, he/she obviously wasnt doing their job. They should have found this a hell of a lot sooner. Even though there may be a projector problem, he is at fault for not stopping it sooner.

Posted by Ron Curran (Member # 3631) on 08-19-2006, 08:34 PM:

Mike, is it possible that it happened on the platter take-up?

Could be that the print found the edge of an upper platter on its way to a lower platter - the angle would be different from start to middle to end, explaining the difference in damage and the wavering. I have seen it happen but it won't be seen on screen till the next screening.

Try a dummy lace-up to a lower platter, using one roller too many or too few.

Posted by Steve Guttag (Member # 268) on 08-19-2006, 08:56 PM:

Yellow scratches are the worst...that means the magenta and cyan layers were scraped away...somewhere, there IS emulsion built up from this event. Normally when you get a scratch like you described, it is from the film dragging on something...not a roller.

Do you have Kelmar cue detectors, by the way? A real dumb thing about them is if you are sloppy, and miss the first roller, the film will drag on the "bat" of the microswitch and cause an emulsion scratch (and you won't see it on the show in progress). All Kelmar had to do is to extend their metal work over to the roller to prevent this sort of thing.

Posted by Brad Miller (Member # 2) on 08-19-2006, 09:13 PM:

Ron, Mike has a Christie platter, not one of those stupid Strong-type platters with two ways to thread the takeup.

I agree with Steve that somewhere there is emulsion powder buildup. The fact that it happened partway through the movie and then stopped 20 minutes later is bizarre.

Mike, does the scratch jiggle left to right a little bit? If so, what is the beat? Is it the same as a Christie roller? A Kelmar film cleaner drive wheel? (Imagine the left to right "beats" of the liquid streaks on a fresh FG application and you will see what I mean. If it is perfectly stationary, it happened in the gate. If it wiggles, it happened elsewhere and that beat will help pinpoint where.)

FYI, the most common misthread I see on older model Christie platters is on the 3 roller takeup cluster. People sometimes thread over the keeper bracket on the first of the 3 takeup cluster rollers, just before going to the takeup speed arm. To achieve a yellow scratch, that would've mean some moron was taking up soundtrack down or did a backwards twist as it was ran onto the surface of the takeup platter.

Posted by Steve Guttag (Member # 268) on 08-19-2006, 09:27 PM:

The scratch starting suddenly can be from the film walking and landing in manner to scratch itself....the scratch disappearing could be from all of the emulsion build up eventually spacing the film away from that which was producing the scratch.

The worst I've ever seen is on a Simplex (single lens) where a gate fastening nut walked off...fell down and wedged itself between the film and the pinch roller in the sound head. Since that gate nut is knureled...it did a REAL number on the film and it cut a wide track.

Posted by Mike Blakesley (Member # 26) on 08-19-2006, 10:15 PM:

The scratch wavers back and forth very erratically (and sometimes goes "on" and "off") with the same rhythm as the platter rollers. It happened last Sunday night and I didn't get to see the fun results until Friday (yesterday). So the print ran 5 shows scratched. I know it happened Sunday because a friend of mine went to the show Monday and told me about the scratch when I got back home.

I'll look for some telltale emulsion buildup. We do have a Kelmar cue detector, so I'll investigate there too.

Posted by Adam Martin (Member # 641) on 08-20-2006, 12:09 AM:

It's possible that the film was knocked partially off the roller during a film check and then caught during the next check, but a yellow scratch seems a stretch for a roller flange.

Posted by Mark Gulbrandsen (Member # 72) on 08-20-2006, 05:01 AM:

quote: Steve Guttag
Do you have Kelmar cue detectors, by the way? A real dumb thing about them is if you are sloppy, and miss the first roller, the film will drag on the "bat" of the microswitch and cause an emulsion scratch (and you won't see it on the show in progress). All Kelmar had to do is to extend their metal work over to the roller to prevent this sort of thing.

I believe that Steve hit the nail on the head! He does have a Kelmar Cue Detector and I believe this is the culpuit too. That dam microswitch.... [Mad]

. Someone happened back into the booth to check on things and found that it was scraping the film. Mike, see if the scratch lines up with the bat on that microswitch.

Mark

Posted by Monte L Fullmer (Member # 2797) on 08-20-2006, 02:24 PM:

..one can create a nasty scratch like that one as well on those SPECO failsafe units that the Christie uses on their P35 units - had an operator who zinged an entire print when he missed the back roller and ran the print in front of the tang on the microswith due to he was in a hurry..

that scratch went completely through the emulsion to the base - a very nasty and big white line.

-Monte

Posted by Jesse Skeen (Member # 586) on 08-20-2006, 07:09 PM:

I saw about 10 films get scratched in one day, it looked like someone had actually gone over one of the rollers on the cue detector, rather than under- sorry I can't explain it better without a picture. It happened on one film and I couldn't tell how they did it, but a couple days later I worked the evening shift and found emulsion dust accumulated against the part of the cue detector where they had it scraping against. There were scratches visible all down the actual film, but they varied onscreen- sometimes there'd be black lines running down everywhere, sometimes one would turn yellow or green and sometimes the scratches were hardly noticable, at least enough so that they asked me to identify which reels were in the worst shape and request replacements of those, rather than the entire print. The slides still looked good though (hadn't upgraded to the 2wenty yet) so the guy who scratched the films didn't get fired for it [Razz]

Posted by Mike Blakesley (Member # 26) on 08-20-2006, 09:56 PM:

Well I went over the whole system last night and could not find any telltale dust anywhere.

I don't think it was dragging on the cue detect, if it was the scratch wouldn't have been as erratic as it is. I guess I'll have to just chalk it up to mysterious circumstances.

Mark G. - the kid who was threading for me last week was Scott, the same kid who helped with the sound work when you were here. He's been threading for about 2 years and never a problem until this one, so it must be an accident. He hasn't worked since we got back but I'll be sure to ask him about it.

Posted by Brad Miller (Member # 2) on 08-20-2006, 10:08 PM:

Looking here...

I notice you have the older model pair of white "stripper" rollers just before the film enters the 3 rollers in the brain. Those have hardly any indention to them and I've seen what you have described happen when a nice big clump of dirt (possibly airborne) gets stuck to the film and pulled into the brain. Granted I've never heard of it being quite that bad, but nonetheless it can happen. It would be worth your effort to change those anyway, as curled film can suffer light scratches down the center of the film when running on those.

Posted by Mark Gulbrandsen (Member # 72) on 08-20-2006, 11:59 PM:

Don't think so Brad since Mike keeps that place spotless.It might be helpful if you could scan a foot or two and post it here so we can see the scratch. Also see if the scratch lines up with any part on the cue detector.....

Mark

Posted by Mike Blakesley (Member # 26) on 08-21-2006, 01:25 AM:

I took a good look at the scratched footage when breaking down the print tonight. It looks like someone took a sharp nail and just held it onto the print...for a good part of the affected footage, it comes and goes with the same rhythm as the cleaner roller. (or possibly the platter rollers as I said above, but I think it's a bit slower than that.) But for quite a while, it's just steady (but still weaves back and forth a bit.)

Definitely not anything stuck in the platter strippers...the scratch is too erratic and intermittent for anything stationary to have caused it. I'll definitely interview Scott about this and see if he can shed any light on it.

(BTW, we actually ended this print last Thursday but I kept it over so I could run it thru on Friday to try to figure out this problem. I put a note in it so hopefully the depot will replace the 2 bad reels.)

Our current movie is running without a hitch so whatever it was, is gone, so that's good at least.

Posted by Mark Gulbrandsen (Member # 72) on 08-21-2006, 08:23 AM:

Mike,

If the film rubbed against the corner of that tang on the microswitch its just the same as running it against a nail!

Mark

Posted by Richard Fowler (Member # 893) on 08-21-2006, 09:12 AM:

I used the Kelmar sensor for one multiplex project...all prints scratched in the first week. We installed a bumper ( screw with plastic roller ) to prevent this. This was with dedicated staff of projectionists. We never used that sensor again.

Posted by Mark Gulbrandsen (Member # 72) on 08-21-2006, 01:54 PM:

Actually the Kelmar Cue Detectors work great and one can shorten that bat to eliminate the problem.

Mark

Posted by Richard Fowler (Member # 893) on 08-21-2006, 02:07 PM:

So when they replace the switch in the future....they can scratch film again...its a design issue [Razz]

it should be "bat proof" [Big Grin]

Posted by Brad Miller (Member # 2) on 08-21-2006, 02:11 PM:

While I agree Kelmar needs to fix this issue, if it really bothers anyone, you can always mount another roller above it to prevent such a thing from happening. On many projectors you can also slide the entire failsafe so far back toward the lamphouse that it makes it damn near impossible to misthread it.

I will keep buying the Kelmar failsafes even with this design flaw because they are hands down the most reliable unit on the market. They NEVER miss a cue.

Posted by Charles Greenlee (Member # 3856) on 08-21-2006, 06:03 PM:

I wish our edge cued speco's were that way. You have to replace the cue after a week or so, or it'll start missing them. I hate edge cueing anyhow. I much liked the ones we had at the Wynnsong, on our Christies, it was a prox. sensor. You could take a peice of black mylar, set the cue on it, and never have to make a cue again, well minus the cues in the credits and after. These black cue segments can be broken down with the trailer sets and used again indefinatly. Though they will eventually wear out. The automation was such that it stepped, and you used knobs to set what each step did. You could do a lens change or close the dowser in mid show if you wanted to. I don't remember the brand or model.