Film-Tech Forum ARCHIVE: HELP! Century poser from hell!

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Posted by Aaron Sisemore (Member # 145) on 01-11-2000, 06:40 PM:

I have 18 years experience with Century projectors but this one seems to have me stumped. One of the theatres I tech has a pair of Century HH single shutter straight gate heads (in separate auditoria) that were bought used and in excellent running condition. Within 100 hours of each other they have both developed the following problem:

There is a very loud noise coming from somewhere in the gear train, it sounds very much like a horse 'galloping'... In addition the horizontal shutter shaft moves back and forth a fraction of an inch in time with the galloping noises. I also have gotten complaints that the picture gradually 'goes out of frame' as this goes on. I have done the following in my diagnosis of the situation:

-Checked the gear train completely for any damaged teeth.. found NOTHING.

-Replaced the intermittent with a known good spare... NOTHING changes

-I have discovered with the second machine ( I have replaced the first one with a working SA as the film had become unwatchable in that house) that moving the shutter timing knob to either extreme would stop the galloping noise and it ran smooth, so as a stopgap until I could get more time to work on this I reset the intermittent to the shutter with the knob in this extreme. Now the problem is back. Also in the worst case with the other projector, the picture began to travel ghost and jump in time with the galloping sound, Thats where I first thought the intermittent was at fault. I am out of ideas at this juncture.

Lubrication doesn't seem to be a factor as the gear train is reguarly lubed by the head projectionist there (a union operator), and I personally have not seen the picture change framing at all in the time I have been diagnosing this problem. HELP!!!

Aaron

Posted by Jon Bartow (Member # 241) on 01-11-2000, 09:29 PM:

Aaron, I had a similar problem with a century SA a couple of years ago. After replacing the intermittent and shutter shaft the problem persisted. Feeling desperate I changed the verticle shaft. Problem solved. The shaft was bent about 1/10mm. near as I can tell this was caused by a bad adjustment of the vert. shaft and the intermittent (i.e. they were not meshing quite perfectly)
Anyway, hope that helps you!

Posted by Scott Ribbens (Member # 180) on 01-11-2000, 10:14 PM:

I have had this happen to me also. A bent verticle shaft can do that to you. Did you check to see if the verticle and shutter shafts were screwed down tightly? They may have gone slightly out of alignment after some running if they were rebuilt. You may be able to loosen these up and make some very slight adjustments and stop the problems. But take your time and do the adjustments in small increments, with the shutter timing adjustment centered. If this makes the problems go away, then make sure you tighten the shafts down tightly. This has worked for me a couple of times. If you just cannot make this problem go away no matter what, then I would agree that the verticle shaft is probably bent, even if it does not look like it is. It does not take much of a bend to cause this as was noted above.

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quote:
"More human than human" is our motto.

Scott

Posted by Steve Guttag (Member # 268) on 01-11-2000, 11:27 PM:

First off, a Century "HH" with a single shutter and straight gate makes no sense...by definition, the HH is a double shutter and has a hardened curved gate (with curved aperture plates too)...but that has little to do with your story unless the double shutter bracket and reversing gear assy is still operating without the shutter.

There are many flaws in the Century design and you have come across one of them...

The shutter shaft has the worst gear ratio of the bunch and has a built-in flywheel called the shutter. As such, ANY problems in the gear train will show up in the shutter shaft as a fore and aft movement (presumming it is loaded correctly).

Main causes are the main drive gear with too much wear or out of round, then the next likely suspect is the GR-207 shutter drive gear, then the GR-234 intermittent drive gear and finally either the shutter or vertical shafts. One way to test the GR-234 is to adjust the "shutter" knob as this will present a different part of the GR-234 to the intermittent (never mind about the stutter trails for the moment) just see if the shutter movement subsides.

All of the above presumes that the drive trains are actually set up right, that is the GR-234 is properly tigtened with it's collar, the bearing bracket is secure (the one that the GR-234 rides in), the gear mesh on all contact points are proper...etc. Any loading, say by a bad bearing, can also bring about the dancing shutter shaft.

Sometimes it helps to remove either the shutter blade when trying to isolate the culprit(s)...removing the blade should calm the shaft down but so you can possibly find something else knocking the drive train.

Good luck, it can be a bare and often more than one thing is contributing to your type of problem.

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"Old projectionists never die, they just changeover!"

Posted by Randy Stankey (Member # 64) on 01-12-2000, 02:35 PM:

I have Century SA-TA proj. so this may not apply...

In my machine, there's a sliding bearing ('knuckle', if you will...) on the vert. shaft that allows the intermittent to move up and down if you move the framing knob. There are two nuts that hold the bearing together. if they come loose, the gear will rise up a fraction of an inch. when this happens, the gears 'unmesh' a little and throw the intermittent out of time with the shutter. It causes shutter ghost and jittery picture.

It only takes a few minutes to fix with a couple of wrenches, not counting shutter timing, etc.

That may not be your problem, but that's my two cents worth!

Posted by Aaron Sisemore (Member # 145) on 01-12-2000, 10:32 PM:

Thanks to all that replied. As soon as I can get the time to get back to this theatre I will recheck the vertical shaft and all the gears, esp. the intermittent drive gear.

Steve: I know the HH is supposed to be double shutter, but these are singles, and without the reversing gearing for the second shutter. The gate is indeed straight, and the aperture plates are the 'notched' type with the thick metal piece that goes into the trap to hold the aperture plate in place, if that helps any.

These machines (sequential serial #s) were together in a former changeover booth that is most likely now DLP-equipped, and from what I have seen when I inspected these machines before installing them were LOVINGLY maintained... Again, thank you all for the assistance, and hope I can be of any for you if the need arises.

Aaron

Posted by Steve Guttag (Member # 268) on 01-12-2000, 10:47 PM:

>>"Steve: I know the HH is supposed to be double shutter, but these are singles, and without the reversing gearing for the second shutter. The gate is indeed straight, and the aperture plates are the 'notched' type with the thick metal piece that goes into the trap to hold the aperture plate in place, if that helps any."<<

Sounds like someone put "C" gates/traps in place of the "H" versions (I've seen this done before). The worst is when someone doesn't do the job completely and uses the "H" gate with the "C" trap...which gives you just one contact point on each side (yes I've seen that done).

I would start with the main drive fibre gear. It is realatively easy to get to, and wears out faster than the other gears. Then move to the GR-207 shutter drive.

If you want to explore the bent shaft or out of round gear theories...check the gear mesh on the constant feeds, rotate the vertical shaft 180 degrees...if there is any difference, something is up...same is true for the GR-207.

Steve

(100th post)

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"Old projectionists never die, they just changeover!"

Posted by Aaron Sisemore (Member # 145) on 01-13-2000, 04:00 AM:

OK, I will definitely try these things omn these projectors, I figure a complete rebuild is on order on one of them anyways, maybe I can get both of them done at the same time...

Aaron

Posted by Tim Reed (Member # 137) on 01-13-2000, 09:32 AM:

Check the shutter bearings. You can't get good bearings anymore, and the ones used as replacements today aren't designed to have much sidewise pressure on the races. They wear out rapidly when installed on the shutter shaft.

The adjustment of the intermittent carriage gib is critical, and if this has ever been removed, is suspect in allowing the framer to creep.

Sounds like you have a double-H that was converted to single shutter, it's not an anomaly, there are tons of them out there.