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Author Topic: Dolby Digital Track Failure Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-07-2005 06:12 PM                        Has anyone been experiencing prints with several reels of bad Dolby Digital. We're showing The Merchant of Venice right now and reel 7 goes into Failure on both machines. Reels 5 and 6 are also bad, but not enough to go to failure. Reels 1-4 are fine. I'd just write it off to a fluke except this is the third print this year with problems. Vera Drake failed on reels 2,4,6. As we run 6000ft reels that means on the same machine reel 1 was good, 2 bad, 3 good, 4 bad. We have a Dolby 650 with Kelmer basement readers. We'll be doing a complete run through of the A & B soon just in case a slight tweek will help, but the alternating reels failing on both machines, leads me to believe the problem is in the lab. Fortunately, we don't run explosion movies, so Merchant and Vera sound fine in Dolby A  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 03-07-2005 07:01 PM                     Re-align your readers. One that is properly aligned should read between 0-3 regularly.  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-08-2005 08:18 AM                        We're planning a complete checkout this weekend, but does that really explain the dramatic differences between reels and features? I checked reel one last night (right before a storm knocked out our power for the evening) and it was reporting a solid 3. Earlier in the day Reel 7 went to failure. Are these differences expected behavior?  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 03-08-2005 09:36 AM                        Are these new prints? If not, it's possible that the track was damaged by the previous operator. Try to get a trailer or reel of film that you know plays with a low error rate. You can then run this periodically as a quick check of reader alignment (i.e. if the error count is significantly higher than it "should" be for that known-good print, then either the track has been damaged or the reader alignment is off. Are you getting proper video level out of the readers? The BACP and cat. 702 have LEDs to indicate whether or not the video level is sufficient. Have you tried using Filmguard? That might improve the error count on a marginal reel.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 03-08-2005 12:40 PM                     quote: Martin McCaffery We have a Dolby 650 with Kelmer basement readers What projector head to you have? If it's a Chrisite P35GPS, these heads DO not like Dolby Digital due to the excessive belt flutter which causes the constant speed sprockets to not run smoothly as with gear driven sprockets. The flutter is very noticable with basement readers with the film is passing around the scanning drum, only in digital, not in optical. Ones with P35 units should use the CAT-70x penthouse heads, which is above the machine's belt jitter condition. -thx Monte  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-08-2005 01:42 PM                        We have Simplex SH-1000 soundheads. We just started using FilmGuard with Merchant of Venice. Merchant and Vera Drake were almost new, so could have been damaged. As an independent, single screen art house in Montgomery, AL, we almost never get brand new prints. I'll give the trailer trick a try and, as I said, we'll be going through the whole system this weekend.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-08-2005 02:02 PM                     When using any simplex soundhead with Film Guard...pay attention to the rubber pinch roller (G-1985)...it will build up with scum that will have the roller bouncing and causing excessive jitter. That rubber surface should be super clean (which means you need to clean it at least once per week). As to Christie...the jitter is there on optical too (same film, same problem) it just doesn't cause optical to fail like digital. The key to their newer projector design is that they now use only one sprocket to feed into and take out of the soundhead so any jitter doesn't result in changing the amount of film in the sound scanning area. So long as it is within the range of the tensioners and the damper, it will track much better. Going to a round tooth belt to minimize cogging of the belt going into and out of the pullies is good too. A Simplex 5-star will perform better digitally with round-tooth belts than the same soundhead with the older square tooth. Steve  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 03-08-2005 02:18 PM                     quote: Martin McCaffery We have Simplex SH-1000 soundheads ..this draws up another question and a possible answer: Being the SH-1000, or commonly known as the "4-star" head, would you know how old this head is? If not, have you checked the oil levels in this head, and possibly have the transmission taken apart, cleaned the sludge out, making sure that the oil fill tube is clear of any of this sludge? Why I'm hitting on these is that this head have a steel worm gear in front of the motor, and the helical gears that drive the sprockets are made of brass. Brass wears down quickly without proper lubrication, thus there would be plenty of slop in the upper and lower holdback sprockets without this lubrication. If there is quite a bit of slop in the upper holdback sprocket, the film isn't being pulled across evenly across the scanner drum, thus error rate would be high. Another 2 possibilities, whereas you have the "4-star" head, that the sounddrum flywheel is the vicous type, not a solid drum type. There could be faults with this flywheel causing the scanner drum not to rotate at a constant speed. Also, check the scanner drum bearings - the front one and the rear one with the flywheel taken off. If any of the two bearings are getting "grumpy" or not turning freely, this can cause irratic rotation in the scanner drum as well and will cause errors to really pop up. These are just mechanical tips to share with you, along of the technical, electronical tips mentioned from other members. Sometimes, it's best to head back to a simple beginning, since this head was originally built to work with exciter lamp, slit lens, photoelectric tube and mirror setup, than being built as a reverse scan LED setup. ..some tips for you. - good luck - Monte  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-08-2005 02:41 PM                        Steve and Monte, thanks for the tips, I will check both. Doubt it is the Filmguard on the roller as the problem precedes the use of FilmGuard but will put this on the cleaning list. Don't know the age of the soundheads, but they are solid drum. Will definitly check for sludge in the pipes. I don't think either of these would explain the dramatic consistent problem from reel to reel replicated on each projector  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 03-08-2005 03:33 PM                     Martin, Anything that hampers the smooth scanning of the film can add to the problem...some dramatic problems are the sum total of a bunch of little problems. While I don't doubt that there are some SH-1000s out there without a damped flywheel, I've yet to see any. Easy test...grab the drum and try to spin it real fast...(jerk it)if it feels like it is slipping a bit...it is a damped flywheel. The bouncing pinch roller has gotten many a soundhead into trouble with digital...a pristine felt pinch roller can't be beat on a "4-star" soundhead...typically tracks better than a penthouse...presumming everything else is up to par. While you are looking at the pinch roller...check the entire thing for cleanliness. Make sure the inboard guide is springing properly. It should be guiding the film, not vice-versa. Make sure the pinch roller casting is not cracked (really can't check that without removing it). It has to hit dead square to the drum. If it is cracked or the hole for the pivot was drilled wrong, it can cock. Buzz track is normally a good indicator...the film should not be wandering and causing the tones to come and go on its own (except at the splice in your loop but it better recover pretty darn quick). Now, presumming mechanically all is right...what about the reader alignment itself? If you have a reader that is dead on, it can deal with a multitude of printing varients. If the alignment is near the edge of a range...what if the printing of the film is also near a limit? It may track on some reels and not on others. Steve  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 03-08-2005 04:48 PM                     Look at the dolby digital info on the film (just in case you don't know, it is in between the sproket holes on the same side of the film as the optical audio track). Use a magnifing glass. Are the "frames" printed correctly, or are they falling off into the sproket holes? Is there discoloration? Do you see a lot of scratches on one reel but not another?  |  IP: Logged Dean Kollet Jedi Master Film Handler Posts: 591 From: Florida State University Registered: Jul 2003 posted 03-08-2005 06:27 PM                     Have you tried running the Dolby WinDRAS software to let you actually look at the block it is reading and see the errors?  |  IP: Logged Martin McCaffery Film God Posts: 2481 From: Montgomery, AL Registered: Jun 99 posted 03-13-2005 12:38 PM                        And the winner is: Damaged print. Went through the whole A/B chain yesterday with loops and Dolby software. Did a few tweeks, but nothing major. But on reel 7 of Merchant of Venice and--Failure. We took a look at the digital track and had what looked like sprocket scratches throughout. No sproket bumps though, so could have been caused by something else. Doesn't explain Vera Drake, but without the print here to check, who knows. Of course, now we are running Tarnation, which isn't digital. Thanks for the tips and suggestions  |  IP: Logged Darryl Spicer Film God Posts: 3250 From: Lexington, KY, USA Registered: Dec 2000 posted 03-13-2005 01:16 PM                    It could have been an issue with the loops being to big hitting something under the intermittent or like on a simplex the back plate that has the two rail like impressions in the back plate  |  IP: Logged

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