Film-Tech Forum ARCHIVE: SRD Area Scratches

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Posted by Mathew Molloy (Member # 666) on 05-12-2003, 05:38 PM:

Frankly, I'm Stumped! I need to figure out what the problem is and fast! Here's the series of events and the problem...

New reflector installed in Xetron 4500watt lamphouse. (Note we are running a Norelco AAII.) A quick focus before the first show was done.

First show of new print of Winged Migration, found that the digital information between every fourth sprocket hole had been severely scratched (on the emulsion side). Some looked more like green blobs than scratches (with a little tail leading up as one looks at it in the gate). This started right with the first trailer after the three or so ads. Also noted a very slight (base?) scratch throughout from beginning of show to end which was bad enough to effect the SRD tracks of the ads as well.

In the gate after the show was a pile of dust on the soundtrack side. There was only a slight build-up on the bands that I had cleaned off. I replaced the bands with new ones. For the rest of the day the piles of dust continued unabated, even though we are using a Kelmar cleaner & Filmguard. I assumed it was still happening.

The next morning I came in to do a fine focus of the lamphouse and discovered it to be severely off and most likely causing a hot spot on the soundtrack side of the aperture plate. I corrected this. I then ran several loops of new film then a 20 minute reel of new trailers five times without any problems. No scratching, nothing.

Today (two weeks later) we get a new print. During the first show the same thing happened but just a little differently -
This time the new trailers seemed to be holding digital okay, but with error rates around 5-6. But as soon as the feature started - bam! I'm screwed again with an error rate of 7-F. (I also noted on the tail of the print, the same emulsion scratches, just smaller than what happened last time). Also there was a dust build-up on the non-soundtrack side unlike last time.

I made sure the bands were nice and clean, but there was some build-up on them after the show. Also note that the green scratches stopped afer the dowser closes...This clues me in to a possible heat problem. I just can't figure out why now that it's focused properly and it didn't happen to the test trailers I ran over and over.

I'm at my wits end so any suggestions would be whole-heartedly welcomed! THANKS! :-)

Posted by Steve Guttag (Member # 268) on 05-12-2003, 05:49 PM:

When you don't know where a scratch is coming from...take a red Marks-O-Lot and coat the area of the scratch on a piece of scrap film...run it for a several minutes in a loop...look for the red dust trails to tell you where the rubs are.

As for the AA2 rubbing the soundtrack...not too many areas contact the film on the emulsion side. The intermittent pad roller, the sounddrum pinch roller, the idler rollers and feed sprockets...only the pad roller really seems like a remotely possible culprit.

Steve

Posted by Mathew Molloy (Member # 666) on 05-12-2003, 05:57 PM:

Thanks for the tip on the red marker. In terms of the emulsion scratch, note that it's occuring between every fourth sprocket hole which leads me to believe it's somewhere in the gate. I thought it might be the intermittent, but not so.

Posted by Richard Hamilton (Member # 321) on 05-12-2003, 06:22 PM:

I had a call a few years ago about a Simplex XL that was putting 2 strange dots on the film at the same spot of every frame. It turned out that the aperature plate was in backwards which caused the two tips of the prongs that hold in the plate to actually slightly rub the film. When the film would stop in the gate, the two prongs were touching just long enough to burn a spot on the film, but then only slightly scratch it as it advanced to the next frame. I'm not that familiar with that projector, but it sounds like it's possibly doing something similar. Also, you said that the slight scratches started from the beginning, but the bad blobs after 3 ads. Possibly the time for whatever part was doing the damage to heat up?

Posted by Mathew Molloy (Member # 666) on 05-12-2003, 07:05 PM:

Richard, thanks!

There seem to be so many variables. The aperture plate is another part I suspect. There are some little grooves in the plate behind the band on the soundtrack side (where someone had done some pounding w/ a hammer I suspect). These have been filling up with the black powder that's being created. I'm sure it's heating up pretty good too.

But there was no powdery stuff after the first show when the damage happened, and again, the hour+ of loops and trailers I tested all ran without problems.

It's going to be a long night. [Razz]

Posted by Brad Miller (Member # 2) on 05-12-2003, 07:08 PM:

Check your film stocks before you waste too much time. Look at a piece of film that was badly abraded and note what film stock it is on. Then cut up a trailer out of the same film stock. You will find some stocks don't scratch as easily as others and that will help you track down the problem faster.

It's got to be in the gate (aperture) or intermittent. There really isn't any other place that can cause that damage unless someone is making a loop way too big and it is slapping, but I doubt it.

Posted by Gordon McLeod (Member # 33) on 05-12-2003, 09:21 PM:

The apperture plate is way behind the film plane on the AA2 I would bet that one of the bands jumped off the lower hook

Posted by Steve Guttag (Member # 268) on 05-13-2003, 07:58 AM:

I have had the AA2 aperture plate burn the film...if the gate depth isn't set properly and one is using a 4KW lamp or larger with a small (1.85) aperture...the plate will eventually buckle forwards and the film swells backwards when the heat hits it...however, that will tend to place the marks in the picture area, not the soundtrack.

The intermittent pad roller contacts the emulsion side of the film and is a double-flange type so it can rub the SRD track, which is why I'd at least look there...the red marker WILL find the rub. Heat related can be found by runing a loop with the douser closed and a different loop with the douser open...if only the loop with the douser open has the problem, you know it is heat and the only area that can be affected is in the gate.

Steve

Posted by Mathew Molloy (Member # 666) on 05-13-2003, 09:54 AM:

Steve, when film is running the back of the bands are touching the aperture plate. Now I thought there was a minute gap between bands and plate with the previous machines I worked with. I contacted that theatre running a pair of AAII's and was told that theirs touch the plate also.

So should the bands be touching the plate? If not, what's involved with adjusting the gate depth?

Posted by Gordon McLeod (Member # 33) on 05-13-2003, 10:01 AM:

If the bands have velvet on them they may touch but the regular steel ones are about 1/32" out

Posted by Steve Guttag (Member # 268) on 05-13-2003, 10:29 AM:

Gord is right on the spacing...the adjustment was only available on the later machines. Where the gate opener knob is placed, there is a metal plate that sets where the "v" groove is placed...using that plate, you can set the depth. I believe the official spec is 1/8" from plate to film.

Steve

Posted by Mathew Molloy (Member # 666) on 05-13-2003, 09:11 PM:

Steve, thanks for telling me about the adjustment via the v-notched metal plate. It was pushed forward and the plate was pushing snug against the bands.

Unfortunately our old shutter blade looks like a pie tin that's been thru WWII and if the gate is moved back any the blade smacks against it...perhaps that's why it was pushed forward to begin with.

I was able to get a small gap there and I set up a new water circulation system. Things seem to be running a little cooler but I ran out of time this morning to run loads of test film.

The next step is to replace the shutter blade - we have a new one but I'm going to get a professional tech. in here to work with me on that. Plus I need to get our new reflector's alignment fine-tuned. With the new blade I can get that gate pushed back a tad more and not run into any more problems.

Thanks Steve, Brad, Gord & Richard for your advice! :-)

Posted by Gordon McLeod (Member # 33) on 05-13-2003, 11:04 PM:

This shows the machine with velvet bands and how the band touches the plate because the velvet pushes it back

This shows the metal band and the gap between it and the plate